Chapter 1 Overview

One challenge of growing and keeping bonsai in NC is our unpredictable weather. Officially we are classified as Köppen climate type Cfa (humid subtropical woodlands and subtropical highlands). This is the same general pattern that historically dominated most of the southeast United States. It means hot and humid summers and mild cool winters, with consistent rainfall year round. Typical summer temperatures are in the 80’s and 90’s (°F) with winter temperatures rarely dropping below freezing 32 °F.

The weather we tend to see is more exaggerated, for a couple reasons. First we sit near the natural boundary between subtropical highs bringing warmer air from the Gulf of Mexico and Caribbean, and the polar jet stream that brings in colder air eastward from the mid-West, and southeast from Canada and the Great Lakes. Small movements of that boundary north or south in winter can push our temperatures much higher in summer or lower in winter than normal. There can be periods of heavy rain or ice, or long stretches of warmer than normal temperatures that can make buds break winter dormancy too early.

Second, climate change has shifted our precipitation patterns. Historically we had fairly consistent rainfall through the year. Now we get extended periods of summer drought (which ironically do not lessen our humidity) that may be punctuated by 2-3 days of heavy rain. This is starting to alter our natural vegetation pattern. Historically our area was a mix of temperate coniferous and temperate seasonal broadleaf forests. As average temperature rises and seasonal droughts become our new normal, our vegetation pattern is predicted to shift towards a temperate or sub-tropical grassland, savanna, or shrubland similar to west Texas or east Africa. This will put greater stress on native trees and any trees being developed in open ground.

The work calendar outlined here assumes our current typical conditions. Timing will need to be adjusted if the weather is unseasonably warm or cold. It also will need to be modified as our local climate conditions continue to change.

Each month is organized around these topics:

• General weather to expect
• Planning and general housekeeping issues
• Digging and potting
• Pruning, wiring and grooming
• Watering and fertilization
• Special notes about deciduous trees, conifers, and tropicals
• Miscellaneous issues for the month

1.1 January

Winter tree coated in ice. Link to original image.

1.1.1 General Weather

Most years the weather in late December through mid- to late January are consistently cold with intermittent rain. Trees stored outdoors tend to stay fully dormant and get enough moisture without additional watering.

1.1.2 Planning and General Housekeeping

Once spring gets here you will have a lot to do in a very short period of time. January (and February) are a good time to make a list of all the tasks that need to be done and get ready.

On a mild day go out and tag or flag all the trees you will be pulling out of the ground and putting into pots. Round up training pots. I recommend putting a nursery pot or container next to each tree you are digging up to make sure you have enough. Then store the containers all together in the same location with a flag or marker saying they are reserved.

Decide which trees will need repotting; tag these with flagging tape and start shopping for a new pot if you plan to move up.

If you expect to be doing a lot of wiring in spring, order several rolls in a variety of sizes. Make sure you have (or order) cut paste, and any tools you will need. They are less likely to be out of stock in mid-winter.

1.1.3 Digging and Potting

If trees or pots were heeled in or covered with mounds of mulch, check that the mulch still is in place.

1.1.4 Insects and Other Pests

Mid-winter is when many growers will spray fruit and other deciduous trees with heavy dormant oil. The oil penetrates cracks in the bark and smothers over-wintering eggs and adult insects. It is especially popular for preventing diseases and infestations of fruiting trees.

If you want to treat deciduous trees with dormant oil, only do it in late January or early February. Spray on branches and trunks only. DO NOT use dormant oil on foliage of conifers, or any tree on which the buds have begun to swell. The oil will permanently scar green parts of trees.

Personally I do not like using heavy dormant oil to control insects on trees; it is too easy to make mistakes. I prefer to use all-season or neem oil, and treat a couple of times each year as needed.

1.1.5 Tropicals

Check all trees for insects and treat if needed with a combination of insecticidal soap and light horticultural or neem oil. The mixture is non-toxic to pets and people. Lay down a plastic dropcloth or shower curtain; both chemicals can make the floor sticky or slick.

1.2 February

Naturalized spring crocus around a wingnut tree in mid-February Link to original image.

1.2.1 General Weather

Temperature swings between cold and warm play havoc with stored trees. It can happen anytime in winter but is particularly likely for us in February. Most years we get a 1-3 week long warm spell at the end of January or middle of February. Some years this warm snap is the start of a slow-moving early spring, but more often the weather turns hard cold again for March, the month when we get our worst snow and ice storms.

1.2.2 Planning and General Housekeeping

Count the trees you plan to pot up or repot this year, and figure out how much soil you will need to fill all of the pots that you plan to use. Then order prepared soil or start buying organic and inorganic matter for mixing your own. Buy or prepare twice what you think you will need. If you are lucky you will only have to make a little more to finish the jobs you have.

This is also a good time to scrub, de-lime, and disinfect ceramic pots in preparation for planting.

1.2.3 Digging and Potting

No trees should be repotted in winter. The only reason to dig up trees now is if they are in imminent danger of being crushed or destroyed. Wait until March if at all possible.

1.2.4 Pruning, Wiring and Grooming

This month is a good time to start choosing which major branches you will remove from trees. Once March arrives you are likely to have lots to do and less time to think about each tree.

Get down on the ground and look at any field-grown trees from all sides. Are there branches that can come off? Mark them using colored twist ties or flagging tape. Do the same with any trees in pots.

Do not do any wiring or pinching, even if a bud or two breaks. Most trees are not ready to be pruned yet.

1.2.5 Watering and Fertilization

Watch pots to ensure they do not dry out completely. As long as the weather is cold and there is occasional rain, you may not need to water much or at all.

Check pots of trees stored outside to make sure leaves or branches have not fallen on them or are holding water against the roots or trunk. If trees or pots were heeled in or covered with mounds of mulch, check that the mulch still is in place.

If a tree decides to break dormancy, limit watering to minimize growth of soft foliage that could be frozen later. Do NOT fertilize it! That only encourages more tender growth.

1.2.6 Deciduous Trees

If leaf buds start to swell and open, deciduous trees become more susceptible to cold and drying out. For trees in the ground, consider providing them with some additional shade. This can reduce the number of buds that break. Keep others in heavy shade to retard bud break.

1.2.7 Conifers

Conifers may resume growing again in mid-winter warm spells. If possible, move them to the shady side of a building (but not into complete darkness.) If a tree decides to take off anyway, water it sparingly to minimize growth

1.2.8 Tropicals

By mid-winter tropicals that spent the summer outside can start showing signs of stress. To give them a boost, pick a day when the weather is above 55oF and put them outside for an hour or two in filtered sunlight or bright shade. Watch out that they do not sunburn, and be sure to move them back indoors at nightfall.

While plants are outside check them for insects and treat accordingly. Also spray the foliage and stems thoroughly with lukewarm water to rinse off any dust or debris. This is also a good time to foliage feed with diluted Miracle-Grow without making a mess indoors. Give the soil a good soaking, and let the pot drain thoroughly. Replace any soil that has been washed away from the roots.

Rinse any slime or debris out of the trays in which tropicals have been sitting. If you had insect problems spray the trays with 70% alcohol or scrub them with diluted bleach then rinse thoroughly. This will kill any insects or eggs hiding on the trays.

1.2.9 Miscellaneous

Sharpen and clean your tools. If you will be digging trees from open ground, sharpen your spade too!

If you use wooden training boxes for field grown trees, this is a good time to build what you need for spring. Personally I switched away from wooden boxes to fabric grow-bags for this step in training. Some people still prefer wooden boxes though.

I used to make them from 1, 12-foot long piece of exterior-treated, appearance grade planking, 0.5 inches thick & ~3 inches wide.

1. Using a chop or circular saw, cut 4 pieces 17.5 inches long, and 4 more that are 18.5 inches long.
2. Pre-drill 2 pilot holes in one end of each 17.5-inch piece of stock.
3. Use 1-inch deck screws to assemble them into a box exactly 18 inches square.
4. Space the 4 longer pieces to form a bottom.
5. Drill pilot holes and attach the bottom planks with deck screws.
6. Line the box with 1-2 layers of landscape cloth, stapled in place. This keeps in soil and prevents roots from circling.

These boxes last several years, and the lining can be replaced each time the box is recycled for a new tree.

1.3 March

Leaves of a downy hawthorn just starting to emerge from their buds in spring. Link to original image.

1.3.1 General Weather

March in Piedmont NC is VERY changeable. We can have 70-degree days on Monday and Tuesday, then freezing rain by the weekend.

Sometime in March, buds on deciduous trees will begin to swell, marking the start of the busy season. There’s a lot to get done, and not a lot of time, so get cracking. If you did not do so earlier, decide which trees will need repotting, and prepare soil. Build or buy training trays, boxes, or pots for trees that you plan to root prune or transplant. Mark branches you intend to remove from trees with white twist ties.

In March, deciduous trees often begin showing signs of root and bud movement. Watch for buds just beginning to swell. When they do, go ahead and root prune and repot the tree. Optimum recovery occurs when trees are kept above 45oF. Shelter newly repotted trees from hard frosts and drying winds, such as in a garage. If the outdoor temperature fluctuates considerably, keep your trees in a cool place to slow the bud break.

1.3.2 Planning and General Housekeeping

If you did not do so last month, decide which trees will need repotting, and start preparing the soil you will need. Also mark major branches you intend to remove from trees.

1.3.3 Digging and Potting

March is the prime month for digging up trees that have been in the ground to fatten up their trunk. They are lifted, root pruned then potted up in oversized containers to recover and begin rebuilding their root system. Ideally this is done JUST as buds start swelling, before the scales of the buds actually start breaking open. Reducing the root mass lowers the xylem pressure and slows down bud break, which protects the tree from drying out.

Digging trees after buds start to open usually still is successful, but there is a slightly higher chance of tip wilt and die-back. Once leaves have opened fully and soft growth begins, trees are more likely to have severe die-back or fail entirely, for two reasons. First, the new leaves will require more water than the reduced root mass can supply. Second, by the time trees leaf out fully, warmer weather usually has arrived which adds even more stress.

March also is the month to start repotting deciduous trees. Again, this is best done just before or as buds start swelling, before the scales of the buds actually start breaking open.

1.3.4 Pruning, Wiring and Grooming

Wait to prune larger branches on deciduous trees until the buds begin to show signs of activity. This ensures that the buds you want to use are alive.

Swollen buds are easily dislodged, so start wiring deciduous trees before buds start breaking. Wrapping wire in florist tape or covering branches with raffia before wiring can reduce damage to delicate bark.

1.3.5 Watering and Fertilization

Start monitoring soil moisture in pots. As trees in pots begin leafing out and temperatures rise, they will start using more water. Do not start fertilizing trees yet. Fertilizing too early stimulates premature bud break and early growth before the weather settles. Wait and let the weather stabilize.

Be very careful not to allow newly repotted trees to become too wet, as it encourages root rot. Place them under a shelter during rainy spells if necessary. To stimulate growth of new feeder roots, allow the soil to get SOMEWHAT dry between waterings. Remember that trees should not be fed for 4 weeks or so after repotting or root pruning.

1.3.6 Deciduous Trees

Watch deciduous trees in pots you intend to repot. When their leaf buds just start to swell, go ahead and root prune and repot the tree. Optimum recovery occurs when repotted trees are kept above 45oF, but still cool. Shelter newly repotted trees from hard frosts and drying winds, such as in a garage. If the outdoor temperature fluctuates considerably, keep your trees in a cool place to slow the bud break.

Once buds open, trees neeed sunlight. However, they should be re–acclimated to full sun slowly. Trees that have not been repotted can be acclimated over 2 weeks. Move them into full sun for a few hours a day for the first week, then extend that time each day over the course of the second week. Acclimate newly repotted trees more slowly. Ideally, newly repotted trees are not fully exposed until four weeks after repotting. If a heavy freeze is expected, move all trees back indoors for the night.

1.3.7 Conifers

Most junipers, pines, and other conifers will follow the same general repotting and wiring rules as deciduous trees, but several weeks later in Spring. You may not need to start repotting them until next month.

To check conifers, lift plants from their pots and inspect the roots. Look for new growth of root tips on the surface of the root ball. New tips are short white or very light colored segments on the end of existing roots. Until those appear, leave the tree alone.

1.3.8 Tropicals

It is still too early to bring tropicals outdoors.

1.4 April

Flowering azalea bonsai in full bloom, mid-April. Link to original image.

1.4.1 General Weather

Temperatures rise quickly in April, and trees react accordingly. Expect to see a lot of changes very quickly. Continue to watch out for late frosts and especially dry, windy periods this month. Protect all trees, but especially repotted ones.

1.4.2 Digging and Potting

Remember, after buds open on deciduous trees, it is too late to root prune or repot until fall. April is the time for repotting many junipers, pines, and other conifers. Lift plants from their pots and inspect their root system weekly. Repot once short white or light colored tips form on the ends of the existing roots.

This is a good time to transplant trees from pots into open ground.

1.4.3 Pruning, Wiring and Grooming

This is the time to prune main branches on these deciduous species:

• Birches
• Beeches
• Cotoneasters
• Hornbeams
• Maples

Wait to prune flowering trees like azaleas, rhododendrons, crape myrtle, and crabapples, until immediately after they finish flowering for this season.

Evergreens to prune now:

• Hollies (prune them before buds open)
• Junipers
• Yews

Pine candles and newly emerging buds on other conifers will emerge and grow rapidly this month and next. Pinch back pine candles that will not be used to extend branches. Remove unwanted buds from other conifers as they break, so they do not draw energy and nutrients away from areas you want to grow.

Wait until mid–summer or fall to do large limb pruning on Hinoki cypress (Chamaecyparis sp.), cryptomerias, and spruces (Picea sp.).

This is a good time to cut larger branches on ficus, just before they end winter dormancy and go back outside for the summer.

Branches thicken rapidly during Spring. Check wires weekly to prevent damage to bark. Some branches may need to have their wire removed before the branch sets in place. When a branch must be wired a second time, reduce the chances of scarring by wrapping the wire in the opposite direction from the first time.

1.4.4 Watering

Infrequent watering over winter may have allowed dry spots to form in the soil of potted trees. To rewet it, submerge the entire pot in a pan of cool rain water deep enough to completely immerse the root mass. Once bubbles stop rising out of the soil, let it soak 5–10 minutes. Remove the pot and let it drain thoroughly. This soaking also helps flush mineral deposits from the soil.

After draining, GENTLY press down on the soil in several places. If a spot sinks suddenly when pressed, there probably was an air pocket. Using a chopstick or pencil, push the soil aside to see if the pocket is still there. If some space remains around the roots, add more soil to fill in the gap. This is also a good time to top off the soil on the top of the pot, since soil settles as it breaks down.

Continue keeping an eye on repotted trees so they do not stay too wet.

1.4.5 Fertilization

When leaves or new needles appear, start feeding trees that have not been repotted with liquid fertilizer diluted to 1/2 the normal recommended concentration. For a tree that has not weathered winter well, some references suggest feeding it the first time with 1/4 strength fertilizer.

Remember to wait for about 4 weeks after repotting both deciduous and conifer trees before feeding them the first time. This gives trees a chance to grow new feeder roots, and reduces the chance of burning new roots.

If you plan to use continuous-feeding pelleted fertilizer, April is a good time to apply it.

“Finished” bonsai specimens may do better with organic fertilizers instead of liquid fertilizers like Miracle–Grow. They tend to release nutrients more slowly and produce less vigorous growth, which in turn helps retain the shape of the tree.

1.4.6 Pest Management

All trees benefit from a good strong spray with the hose to wash away dirt and dust, accumulated cobwebs, or newly emerged aphids that overwintered.

Something I learned from an Ag Extension brochure is that many scale insects die over the winter, but leave their tough shell as a shelter for the next generation of eggs and tiny crawler-stage larvae. If you catch and treat scale first thing in spring, just as the crawlers emerge from under their parent’s shell, you greatly reduce their population for the entire year.

Watch new growth EXTREMELY closely in April. Tender new leaves and shoots are the areas where pests will go first. If you do not let them get a foothold now, you are less likely to have problems later, for two reasons. First, predatory insects will soon be up and moving, and will help keep pests under control. Second, as foliage hardens off, it is more difficult for sucking insects to feed on it.

If sucking insects show up, spray with a mix of horticultural oil and insecticidal soap. Only spray if you see insects feeding. This mix does not work as a deterrrent.

April is when you should start a fungicidal spray program. Not everyone thinks preventive spraying is needed or good practice. Given how common leaf spot and other diseases are in this area though, you should seriously consider it. Trees that are particularly susceptible to fungus include all fruiting trees (crabapples, flowering quince or plum, cherries), oaks, and many Japanese maple cultivars.

Fungal sprays do not have to be noxious chemicals. Two very good choices for routine spraying are potassium bicarbonate and Bordeaux mixture. Potassium bicarbonate is basically baking soda with the sodium replaced by potassium (which trees need as an essential nutrient anyway.) It changes the pH on the leaves so that fungal spores do not germinate or grow. Bordeaux mixture contains copper sulfate and calcium hydroxide. It prevents growth of downy mildew, powdery mildew and related fungi. It only works as a preventive treatment; it does not knock down active fungus.

One fungal pest that appears in April and is not easily controlled is cedar apple rust. This fungus alternates between two hosts. The fungus causes brown spotting of leaves on apples and crabapples. Junipers and red cedars (which are junipers actually) are the second host. Here the disease makes small branches grow woody balls similar to leaf galls. The cedar balls can be anywhere from 1/4 inch to over an inch in diameter. When mature each cedar ball will have orange “fringe” that sheds millions of spores, ready to spread to apple trees and repeat the cycle. Spray cedar and apple trees with a commercial fungicide labeled for use on cedar apple rust. If you find the apples, gently break them off from the infected branch before they mature.

April also is when you need to watch out for fireblight, which is an infection by the bacterium Erwinia amylovora. It attacks pome fruit trees and related plants in the Rosaceae. Pear (Pyrus species) and quince (Cydonia) are extremely susceptible. Apple and crabapple (Malus species), and firethorns (Pyracantha species) also are frequently damaged. Fire blight is less common on hawthorn (Crataegus species), Spiraea, Cotoneaster sp., serviceberry (Amelanchier species), mountain ash (Sorbus species), and other related plants. New branch tips turn dry and brown as if they have been cut off and left to dry in the sun. Branches turn black as if scorched. Fireblight runs in cycles; some years it is very bad, and in others, almost non-existant. Trees showing signs of fireblight need to be treated promptly, as fireblight continues burning branches back until summer heat sends it into dormancy. Severe infections can kill even large trees. Prune branches back 1-2 inches before the first blackened twigs, then spray with horticultural streptomycin. There is no other treatment available.

1.4.7 Tropicals

We may get late cold spells, so wait a little longer to start moving tropical and semi–tropical species out for the year. If hardy trees were stored in a shed or garage rather than outside they will need time to readjust to wind and sun. Place them out for a few hours the first day, then lengthen their exposure time by a couple of hours each day for a week.

1.5 May

A Japanese Maple (Acer palmatum) in the Portland Japanese Garden, in full leaf in April. Link to original image.

1.5.1 General Weather

This is the month when our weather settles and starts to heat up. May also tends to be when rainfall becomes more spotty and summer drought cycles start.

1.5.2 Digging and Potting

This is the last month for repotting conifers safely. At this point deciduous trees have leafed out, and should not be repotted. Watch water levels in repotted trees.

It is still safe to transplant trees from pots into open ground, but do not try to lift trees from the ground into pots.

1.5.3 Pruning, Wiring and Grooming

Continue to remove unwanted buds from conifers as they break, so they do not draw energy and nutrients away from areas where you want growth. Prune azaleas, rhododendrons, crape myrtle, and crab apples very soon after they have flowered, so they have time to set next year’s flower buds.

1.5.4 Watering and Fertilization

With full foliage and windy or warm weather, trees will start using much more water. Do not assume rain will do all your watering for you. Leafed out trees act like an umbrella and shelter the pot from anything but a downpour. Check pots for adequate moisture, even in wet weather.

Most trees should be on a biweekly fertilization schedule by the end of this month.

1.5.5 Insects and Other Pests

Start checking your trees routinely (ideally weekly) for insects and fungal diseases.

1.5.6 Tropicals

Warmer weather means you can start moving tropicals out for the summer. They will need to acclimate to outdoor conditions. Move out into the sun for no more than 20 minutes the first day, then back into shade. Lengthen exposure time slowly over 2-3 weeks. If the weather forecast predicts a cold night, cover them with a sheet or bring into an unheated garage.

Remember that indoor leaves are much softer and can sunburn. Acclimate trees by gradually exposing them to the sun for longer times over several days. The preferred conditions can be very different when tropical trees go outdoors. Ficus and myrtles prefer bright shade or AM sun with even, moderate water. Fukien tea and serissa prefer full sun (allow some shade on hot afternoons) but very moist soil. J jades develop their best growth and color when they bake in nearly full sun and semi–drought conditions.

1.5.7 Miscellaneous

Early May is a very good time to find bargains on bonsai starter trees. During March and April, container stock rarely spends more than a few days on vendors’ shelves. By the end of April what is left are spent flowering shrubs and trees passed over because of broken branches or misshapen trunks.

Look for trees with good trunks and nebari but damaged branches, gather them into a group, then offer to purchase the lot at half-price. Many nursery managers will jump at the chance to get rid of damaged goods while they still have the chance to break even. If you wait for the vendor to mark them down, the trees are likely to suffered additional stress. So go ahead and ask: all they can do is say no.

I learned of another good source of starter stock when a falling limb broke off the top of an ornamental crabapple. When I cut it back the rootstock sprouted new shoots that will make a nice tree with some training. I learned that most apples are grafted onto dwarf crabapple rootstocks. So if you find a half-price apple or crabapple tree that has a nice base taper, grab it. Next February cut back most of the top growth to force the rootstock to re-sprout. You are likely to get a nice small-leaved crabapple.

1.6 June

Western or Sierra juniper (Juniperus occidentalis var. australis), on steep rocky slope above the edge of Agnew Lake, Ansel Adams Wilderness, Sierra Nevada. Link to original image.

1.6.1 General Weather

June heats up quickly. Trees in full sun will need some protection from mid-day sun until fall. The quickest way to shade a large group of trees is to hang shade cloth over them. You can buy shade cloth rated to specific percentages (10% shade, 40% shade, etc.) from greenhouse suppliers. Plain burlap is a less expensive option for a small number of trees. Buy a roll of loosely woven fabric and hang it a few inches above the top shoots. This produces about 33% shade, but the exact value depends on the brand you buy. If one layer does not provide enough protection, use 2 layers.

1.6.2 Digging and Potting

It is still possible (though not a good idea) to transplant trees from pots into open ground. Any trees transplanted to the ground will need to be watered regularly. Do not try to lift trees from the ground into pots.

1.6.3 Pruning, Wiring and Grooming

Healthy trees should have ample new growth now. Focus on trimming new shoots rather than major branches. Left unchecked, new shoot growth will be more rapid and vigorous at the apex of most trees.

• To keep a tree at its current height, trim soft green shoots back hard to allow more light and nutrients to be distributed to lower branches.
  
• To increase height or thicken a trunk, let the apical growth extend freely and keep side branches pinched back.
• To thicken all parts, cut back half of the apical growth to stimulate the side branches to extend. Then let both the apical stem AND side branches elongate freely for the rest of the season.

If you topped a large trunk in fall or spring, there should be numerous small green branches sprouting from the top and trunk. Choose the ones you want to develop then remove any unneeded sprouts. Use guy wires and staking to establish the new apex and branch framework now while shoots are still soft. This will push resources into the branches you want to keep.

1.6.4 Watering

As summer heat settles in, container nursery managers recommend setting and sticking to a routine watering schedule. Trees in the ground can tolerate intermittent wet and dry periods because there is a large water reserve in the soil that roots draw closer by capillary action. Trees in boxes and pots do not have this reserve available so extremes of wet and dry are more stressful.

ANLA Guidelines recommend watering on a regular schedule to limit root heat stress and adjusting the AMOUNT of water given to maintain a stable range of moisture between soil particles. Bonsai soil is tailor-made for this. Say you are watering daily in the morning, and one tree has not dried out from the day before. Rather than skip that tree entirely for a day (and risk it drying out), give it a small dollop of water. After a few watering cycles, you will develop a sense of which trees need more or less water.

This watering strategy can lead to mineral build-up in the soil over time. If there has been no heavy rain to flush pots for you, every week or so water all trees so the water flows freely from the bottom of the pot. This flushes salts without the trees having constantly over-wet roots. Doing this a day before using liquid fertilizer can improve nutrient distribution in the soil mix as well.

1.6.5 Fertilization

If you want to push growth of trees in large boxes or the ground, use full–strength liquid fertilizer, and apply directly each week with a hose-end sprayer. Spray both soil and leaves for foliar feeding.

For well-developed trees in pots that you do not want to push, only feed every OTHER week using half–strength fertilizer. Alternatively switch to an organic fertilizer that becomes available more slowly.

Heavy rains can leach micronutrients from soil, particularly iron. Watch for leaves turning yellow in between the veins, which is a sign of iron deficiency. Treat with a solution of Ironite following package directions.

1.6.6 Insects and Other Pests

Regularly check new growth for aphids, mites, cushiony scale, and mealybugs; check older branches for hard-shell scale insects. Tiny spiderwebs or pale mottled spots on foliage or needles are a symptom of mites. Inspect both top and undersides of leaves for signs of mold, mildew, or leaf spot diseases.

Treat as needed based on the pests or diseases that are present. If you have certain trees that develop disease or are attacked by pests almost yearly, consider putting them on a routine preventive spray regimen.

Start watching for signs of fire blight. I do not remember a year when it did not occur, but the severity of the outbreak changes from year to year. This disease attacks species in the rose family. Keep an eye on pyracanthas, crabapples, cherries, and related flowering trees. It enters flowering spurs, then girdles the branch, making it look as if the branch has been dried out by a fire (hence the name).

If you see tips of branches suddenly turning brown and dying, DO NOT WAIT TO TREAT. Fire blight spreads quickly and aggressively. Purchase agricultural streptomycin from a farm and garden store, and apply according to label directions. For infected trees find the point where the brown, dead cambium changes to green live cambium. Move another 1-2 inches further into live cambium, then cut off the branch or trunk. Immediately place the infected cuttings in a plastic bag for disposal. Do not leave clippings from fire blighted trees lying around, as they continue to shed spores as they decay. Disinfect all tools that contact blighted trees with 10% bleach to prevent spreading the infection.

Even with aggressive pruning, fire blight can kill the tree.

1.6.7 Tropicals

Tropicals should be back outdoors by now.

1.6.8 Miscellaneous

Once temperatures exceed ~85oF, some species enter summer dormancy. Japanese maples are quickest to slow down but beeches, hornbeams, native maples, and many cool-adapted conifers can undergo summer dormancy too. Most trees are not adversely affected by dormancy, and will restart growing when temperatures are more moderate. Beeches are the exception; they can be permanently damaged by overheating. If you have beeches in your collection, consider moving them to full shade in the hottest part of the day.

One reference suggests that summer dormancy may not be due to temperature alone, and that insufficient macronutrients to support growth contributes to it. This could explain why some growers do not see summer dormancy; their feeding regimen stimulates growth more than summer heat prevents it.

Insufficient water can make a tree wilt or scorch the leaves irreversibly. If a tree does suddenly wilt or drop all its leaves it can often be saved. Strip off the damaged leaves by running your hands from trunk to branch tips; only remove what comes off easily. Move the tree to a location in bright shade, and water thoroughly. Spray the trunk and branches so they are dripping wet too. After this, mist the tree daily to keep the buds moist, but do not overwater. The dormant leaf buds should pop, replacing the dead leaves. DO NOT leaf prune the tree, and keep it in partial shade for the rest of the year.

1.7 July

Summer heat brings out flowering crape myrtles. Link to original image.

1.7.1 General Weather

Hot, humid, sticky. Repeat. Welcome to high summer in the Southeast. It is not unusual for us to get little or no rain from late June through July and much of August.

1.7.2 Digging and Potting

No. Just no.

1.7.3 Pruning, Wiring and Grooming

Continue monitoring new growth, and remove what you do not need to fatten the trunk or build branches. It is safe to remove new seasonal growth, but it is not a good idea to remove big branches.

1.7.4 Watering and Fertilization

Monitor your trees in pots carefully, and check them at least once daily to ensure the pots do dry out too much. Watch trees in the ground as well. Heat combined with declining rainfall will put stress on trees planted in the open ground. Trees being ground–trained will very likely have shallower root systems compared to landscaping shrubs or trees that will have roots extending many feet down. Pre–bonsai trees often have roots less than a foot deep, and may be situated in faster draining soil.

Until cooler weather and steady rain returns, regularly check the soil moisture around trees growing in open ground too. If they are dry an inch or more down, water them slowly, thoroughly, and deeply. One gallon of water applied in one minute to a bare soil surface will puddle and run off, but not penetrate more than a couple inches. That same gallon applied over the course of an hour disappears into the soil. It penetrates deeper, so less is lost by runoff or evaporation. Consider snaking a porous soaker hose between your trees; move it every other week so capillary action wets the soil in the root zones more evenly. Alternatively, install a drip irrigation system. They are simple to assemble, place water in exactly the right spot, and waste very little water.

Put mulch around in-ground trees to reduce evaporation and keep the soil particles hydrated. Pile soil conditioner or finely shredded pine bark mulch 1–2 inches thick in a ring at least twice as large as the tree’s crown, but keep the mulch pulled back from the trunk to prevent disease. Mulch also shades the roots and provides evaporative cooling that reduces plant water stress.

Finally, incorporate ample organic matter into the soil BEYOND the hole where a tree is planted. Bark and other organic matter holds moisture, and lets water percolate deeper than clay alone. Amending the soil well out from each tree’s roots also provides a larger storage reservoir for water that can migrate by capillary action into the root zone.

1.7.5 Insects and Other Pests

Continue checking weekly for aphids, cushiony and shell scale, and mealybugs. Look especially for tiny spiderwebs or pale mottled spots on foliage or needles from spider mites.

Inspect both top and undersides of leaves for signs of mold, mildew, or leaf spot diseases.

1.7.6 Tropicals

Tropical species should be outside for the summer by now. Preferred conditions can be very different when tropical trees go outdoors. Ficus and myrtles prefer bright shade or AM sun with even, moderate water. Fukien tea and serissa prefer full sun (allow some shade on hot afternoons) but very moist soil, while jades develop their best growth and color when they bake in nearly full sun and semi–drought conditions.

If you want to coax maximum growth from tropical trees, switch to full–strength fertilizer. Tropicals in particular can put on tremendous growth if fed this way.

1.7.7 Miscellaneous

July is a good month to leaf prune a tree if you want it to have high quality leaves in September and October.

Pay attention to weeds in pots, as they can grow extremely quickly this time of year. If a weed’s roots are embedded too deeply to pull it without injuring a tree, you can push the tips of a pair of metal scissors just below the soil, and snip the main roots of the weeds, then break off the top. The decaying roots are unlike to harm the tree. Alternatively, use Roundup or other glyphosate-based herbicide to kill it. Dilute the herbicide according to package directions. Wrap the tree in plastic to keep any stray solution off of the leaves. Using a paint brush (NOT a spray bottle), coat the leaves of the weedy plant with herbicide. After the herbicide dries, you can unwrap the plastic. The glyphosate will kill the weed roots, but will not migrate through the soil.

1.8 August

A bald cypress, Taxodium distichum, on the Lower Mt. Fork River, Oklahoma. Link to original image.

Scenic view through Spanish moss covered cypresses in coastal South Carolina. Link to original image.

Cypress knees (pneumatophores). Link to original image.

1.8.1 General Weather

Summer heat continues through August. It also is the month that we are most likely to have drought.

1.8.2 Planning and General Housekeeping

Rotate trees 1/4 turn at least once a week so that all sides get equal light.

1.8.3 Pruning, Wiring and Grooming

Heat slows down extension growth of many deciduous trees. Energy now goes to finer tip branching and thickening of existing structural branches. Focus on trimming new shoots rather than major branches. Do not let branch tips get too congested.

Branches wired in early spring may have already set in place. Check for tight wires, and remove or rewire as needed. Pay VERY close attention to wired branches that you are trying to thicken as well. Wire scars on the branches and trunk at this stage can take years to fill out.

1.8.4 Watering and Fertilization

Keep a watering can or hose nearby, as extreme heat makes pots dry out rapidly.

Continue to feed trees regularly with half–strength or full-strength, balanced fertilizer.

1.8.5 Insects and Other Pests

July and August is the peak period for chewing insects, Japanese beetles in particular. They can defoliate a birch, elm, or other deciduous tree in a day. Not all trees are susceptible to Japanese beetles and their evil kin, so only treat if you actually see them starting to feed on a tree. If you have a specimen that is just beginning to be attacked, cover it with a piece of floating row cover mesh, which protects it without limiting light or air circulation. If you see shredded leaves or find large numbers of feeding insects, you will need to change to chemical controls. Beetles and larger chewing insects usually are not affected by soaps or repellents; dust them with Sevin (carbaryl) or spray with malathion.

If you never see beetles, but have leaves with round pinholes chewed out of them, you likely have flea beetles. Treat the same as for other beetles.

1.8.6 Deciduous Trees

You may notice that some trees need slightly LESS water now. This might seem counter-intuitive until you think about the biology of growth. Summer heat signals the extension growth of many deciduous trees to slow down, and they put energy into finer tip branching and thickening of existing structural branches.

1.8.7 Conifers

Conifers are in a period of peak growth, that is concentrated at the apex. To maintain a tree’s current height, trim soft green shoots back hard to allow more light and nutrients to be distributed to the lower branches. To increase height or thicken the main trunk let the apical growth extend freely, and pinch back side branches. To thicken all parts, cut back half of the apical growth to stimulate the side branches to extend. Then let both the apical stem AND the side branches elongate freely. Remember to keep the health of the tree in mind. If a tree is stressed by the heat or other problems, do not remove its healthy growth.

1.8.8 Tropicals

Tropicals should be growing rapidly. Soft pinch mature specimens to maintain shape. If you have training stock, now can be a good time to pick the main scaffold branches and start wiring trunks to shape.

1.8.9 Miscellaneous

Most of our local mushrooms fruit in the fall, so starting in August you may see mushrooms in pots. Most of our locally abundant species feed on decaying materials, not living wood. So do not be alarmed unless you see them growing out of exposed roots or the trunk. Definitely do not spray with fungicide, because this can kill vital mycorrhizae that help roots extract nutrients. Just pick the fruiting bodies out.

1.9 September

Trident maple in September, just starting to hint at the coming fall colors. Link to original image.

1.9.1 General Weather

From late August through September into early October is another challenging period in our annual cycle. We will begin to have some cooler days, with drier air and breeze. Yet other days may be just as brutally hot and humid as July. Those lazy, predictable summer routines of watering and feeding need to change too.

1.9.2 Planning and General Housekeeping

It is a good time to start planning what you will do with your trees during the winter. Tropicals will likely need to come indoors by Halloween if not sooner. Leaves start falling in mid–October, and the first frost date for Forsyth County is November 15th. Non–tropical deciduous trees should be headed for their winter quarters by that date, or shortly thereafter. Conifers can stay out until harder freezes are expected.

1.9.3 Digging and Potting

Not many people realize that there is a second repotting season in fall. You can repot trees successfully on cool overcast days, or in cooler days the first half of October. Personally I prefer to repot relatively finished trees in spring, and reserve fall for repotting seedlings and ground stock I am growing out, for two reasons. First, I start seeds in deeper trays so seedlings have enough soil to spend their entire first summer in the same container. Second I tend to root prune ground stock hard when moving it from standard containers to bonsai training containers. Repotting both in September gives them time to recover before first frost, and lets the root mass rebuild during winter.

1.9.4 Pruning, Wiring and Grooming

Some species prefer having major pruning done this time of year. For flowering quince, trim new growth back to 2 nodes, and remove all basal shoots you are not trying to develop. Heavier pruning can be done on main branches of cryptomeria, euonymus, crape myrtles, and spruces. Lighter pruning of extension growth can be done on azaleas and pyracanthas. For flowering crabapples and cherries, cut back any rampant shoots and unwanted older branches. On pines, remove old needles and crowded twigs.

1.9.5 Watering and Fertilization

Water use is going to be less predictable, so it will be a good idea to check the soil moisture in your pots daily. You may find some trees start using more water as they mobilize and re–sort nutrients in preparation for autumn. Other trees might have gone dormant in the heat, and will start using more water as photosynthesis kicks back into high gear. Still other pots may remain damp for much longer than before. As always, trust touch not sight; does the soil feel cool and moist? If so, skip watering.

Most trees should have been on a routine schedule of biweekly feeding for the summer. It is time to adjust that schedule to aid fall hardening and winter dormancy. Based on my reference books, we can divide trees into 4 groups: evergreens and conifers, deciduous foliage trees, fruiting trees, and tropicals.

1. Conifers and evergreens can withstand colder temperatures, and will continue growing for a while yet. Continue their summer feeding regimen until early October. This group includes cedars, cryptomeria, Chamaecyparis, juniper, spruce, larch, yew, and pines. Caution: while hollies are evergreen, they prefer to be treated like fruiting trees.

2. Broadleaf foliage trees include maples, birches, hornbeams, cotoneaster, hackberry, hawthorns (if not fruiting), Lonicera sp., azaleas, and elms. They need to start hardening off this season’s growth. Stop fertilizing them entirely, or switch to a nitrogen–free or very low–nitrogen fertilizer. Do not bother looking for N–free liquid fertilizer locally; you will need to purchase it online.

3. Fruiting trees develop nuts or fruits this time of year, and often will wait until very late in the season to form the bulk of next year’s buds. This group includes oaks, hawthorns (if fruiting), hollies, crape myrtles, crabapples, and wisteria. They need some nutrients to complete the process, but still should start hardening off. Cut them back to 1/4–strength liquid feed every 2 weeks until leaves start falling, then stop entirely.

4. Tropicals should stay on their normal summer schedule. When they come indoors (more about that below), growth is likely to slow down while they adjust. During this time feed with 1/4–strength fertilizer every two weeks. If growth resumes, return to a summer feeding schedule. Other tropicals may go dormant for a time; if so, do not feed them until new growth appears, or they go back outside next spring.

1.9.6 Insects and Other Pests

Sucking insects soon will lay their eggs that will overwinter. Consider spraying trees with the first of two rounds of summer horticultural oil (NOT dormant or winter oil) to smother the adults before they can spawn. If you do not plan to spray twice, skip this one and spray once near the end of October or early November.

Follow the label directions, and check for compatibility with your particular tree species. Hint: I also use summer oil treatment to de–bug tropicals just before they come inside.

1.9.7 Miscellaneous

The period when you can leaf–prune trees safely is over. If you have not done it already, skip it for this year and let the tree build up stores and harden off.

1.10 October

Maple (Acer japonicum) in Showa Memorial Park, showing full autumn color. Link to original image.

1.10.1 General Weather

Warm weather often extends into October, but do not be fooled. The hard freeze date for this area is Nov. 15th, just a few weeks away. Trees may need to switch from hot to cold conditions very quickly. In a couple of our most extreme years, I have seen trees go from green leaves to frozen and crispy without ever taking on fall colors, and without dropping their leaves. If this happens, leave the dead leaves alone; they provide some additional protection for buds that may not have set fully before the cold set in.

1.10.2 Digging and Potting

ALL trees that are in the ground to fatten their trunks should be root pruned every 2-3 years. Trees to be moved to pots next spring also should be root pruned to encourage formation of a compact root system. If you know of “wild” trees that you want to collect, you can get a head start by root pruning them the fall before you lift them in spring.

I recently learned that some older nurseries root prune in fall, then lift trees in spring, give them a 1/3 to 1/2 turn, and put them right back in the ground. This helps improve growth on the sides away from the sun.

The best time to root prune depends on the local climate. In areas like ours with a mild winter climate and shallow frost zone, tree roots will continue to grow during winter. So our ideal time for root pruning in our area will be from late October (when days finally are cooler and leaves begin to go dormant) until mid-December. Most trees will recover just fine and build extensive new roots by spring digging season.

The general rule is to root prune 10-12 inches out from the base of the tree for every inch of trunk diameter. Draw an imaginary circle around the tree, and sink the blade of a square-nosed shovel vertically and as deep as you can go, all the way around this circle. Water the tree well to settle the soil in the slots you just cut. Do not lift the tree; wait until spring to lift it or turn it. The whole process will take 2-5 minutes per tree. If you are pruning a wild tree, tie a dull colored piece of string around the trunk so you can find the tree again, and not accidentally dig up an unpruned tree.

If you think this will not make much difference, keep in mind that this is standard nursery practice. Personally, I saw a tree I knew had thin roots triple its feeder root mass from September to March after root pruning.

Early autumn is a VERY good time to transplant stock trees from nursery pots into open ground. Most trees establish new roots more quickly in cooler weather, and are less likely to dry out. If you replaced the soil when you removed dead trees, you can safely plant new stock in them, provided you corrected any other problems (poor drainage, too much shade, etc.) that might have contributed to the last tree’s demise. Remember to water newly planted stock regularly for several months as it gets established.

1.10.3 Pruning, Wiring and Grooming

In general, stop pruning and grooming, and let trees spend their energy hardening off for winter. The only trees that should be pruned routinely now are yews.

Check ALL wires to see if they are biting into branches. To reduce the chances of cold damage later, remove wire from all branches that have set, so any fine cuts in the bark can heal over before frost.

1.10.4 Watering and Fertilization

Continue watching pots individually, and adjusting the watering frequency accordingly. Cut back some on water, and let pots dry a bit more than you did in summer. This will encourage the tree to prepare for dormancy.

It also is time to start cutting back on feeding. The best time depends on the tree type.

1. Broadleaf foliage trees (maples, birches, hornbeams, cotoneaster, hackberry, non–fruiting hawthorns, honeysuckles, azaleas, and elms) should not be fertilized past mid–October.

2. Go ahead and stop feeding coniferous evergreens (cedars, cryptomeria, Chamaecyparis, juniper, spruce, larch, yew, and pines). Yes, I know many growers say the trees will stop on their own, but I think trees benefit from the hint to slow down their growth. More important, I am a cheapskate; why give them fertilizer if they won’t use it?

3. Continue feeding late–fruiting trees (oaks, fruiting hawthorns, hollies, crape myrtles, crabapples, and wisteria) with 1/4–strength liquid feed every 2 weeks until their leaves start falling, then stop.

4. Tropicals should stay on their normal summer schedule. When they come indoors (more about that below), growth is likely to slow down as they adjust. During this time feed with 1/4–strength fertilizer every 2-3 weeks. If growth resumes, return to a summer feeding schedule. Other tropicals may go dormant for a time; if so, do not feed them until new growth appears, or they go back outside next spring.

1.10.5 Insects and Other Pests

I recommend waiting until early November spray outdoor trees, so that insects do not come back and lay a second round of eggs. You SHOULD go ahead and spray them with a round of insecticidal soap if you see obvious adult and larval insects.

1.10.6 Tropicals

It is time to move tropicals indoors. As a rule of thumb, tropicals can tolerate a night or two of cool weather, but they do not like sustained temperatures lower than 50oF, and most prefer to stay above 55oF. So watch the weather and plan ahead. If the weather cools suddenly, move tropicals into a garage or shed until the temperature is more moderate or you have time to move them to permanent winter quarters.

Spray tropicals with summer horticultural oil (NOT dormant or winter oil) to smother overwintering insects and de–bug them just before they come inside. Follow the label directions, and check for compatibility with your particular tree species. This mixture is non-toxic to pets and people. I routinely spray all tropical trees with it before bringing them in for the winter.

1.10.7 Miscellaneous

If you have trees in open ground, inspect them carefully. Pull out any that have died now rather than later, as they can harbor insect pests. Also think about pulling out any trees that have areas of die-back that extend below ground. The tree may be alive now, but root rot will very likely kill the remaining roots over winter. To avoid potential soil fungal diseases or pests, be sure to also remove the soil that was immediately around the roots as well. If you need to refill holes to protect adjacent trees or to prevent erosion, use a mixture of 2 parts black topsoil and 1 part pine bark soil conditioner (both from Lowes or Home Depot). This mix is inexpensive, can be dug back out easily, and lets water percolate deeply around the remaining trees.

Consider mulching healthy trees in the ground with 3-4 inches of finely shredded pine or cypress bark. We tend to think of mulch in terms of protecting from cold, but it also can help the soil hold on to water. If you mulch in-ground trees BE SURE to water them deeply and thoroughly BEFORE putting down mulch. Do not push mulch right up to the roots or trunk of a tree; it invites voles, insects, and fungal attack. Keep mulch at least 1 inch away from the trunks of trees.

After mulching, water deeply but less frequently. Applying small amounts of water frequently will keep the mulch moist, but the water will not penetrate to the tree roots.

One strategy I’ve read for watering trees deeply is to use a lawn sprinkler as follows:

• On Day 1, set the sprinkler so all trees are being watered evenly. Let the water run for 30 minutes, then turn it off 30 minutes. Turn the water back on for 30 minutes, then off again. Repeat the pattern for 8-10 hours.

• On Day 2, apply 4 inches of mulch in a circle at least 3 inches larger in diameter than the tree’s crown. Using the sprinkler, water again for 30-60 minutes to wet the mulch thoroughly.

• On Day 5, water for 4 hours, following the 30 minutes on/30 minutes off pattern.

• On Day 11, then every 6-7 days thereafter, water for 4 hours using the same 30-minute ON/OFF pattern. Anytime there has been significant rain, wait at least 5 days before watering again.

Yes it is tedious but if you have lost trees in past winters, it may be worth trying this out.

1.11 November

Street lined with dawn redwoods in November. Damyang, Jeolla province, South Korea. Link to original image.

1.11.1 General Weather

Expect our first frosts this month, and greater rainfall. November tends to be cold and wet.

1.11.2 Digging and Potting

Continue root pruning trees that are in the ground.

1.11.3 Pruning, Wiring and Grooming

Check ALL wires one last time to see if they are biting into branches. To reduce the chances of cold damage later, remove wire from any branches that have set. Also consider removing wires for winter, and planning to rewire next spring (wrapping in the opposite direction).

You should not be pruning branches at this time. However, with leaves off it is a good time to look at branch structure, and start choosing any branches that might be removed during spring pruning. Also look at foliage pads on evergreens. Take photographs before storing trees, so you have a reminder to look at as you plan. Mark any branches that will likely need thinning or rebuilding in spring with a loosely attached twist–tie or piece of colored yarn.

1.11.4 Watering and Fertilization

Continue watching pots individually, and adjusting the watering frequency accordingly. Continue to cut back on water, and let pots dry a bit more than you did in summer. This will encourage the tree to finish going dormant. Drier conditions also encourage trees to pull nutrients back from the falling leaves, rather than just letting them go. Good autumn color is a sign that the trees are pulling nitrogen and other nutrients back from the leaves, for storage in preparation for spring.

By the end of this month you should stop fertilizing all outdoor trees for the year. Tropicals that came indoors are still adjusting; IF growth resumes feed with 1/4–strength fertilizer biweekly for a month, then return to a summer feeding schedule as growth resumes. If a tree remains dormant, do not feed it.

1.11.5 Insects and Other Pests

Most insects have disappeared for the year.

1.11.6 Tropicals

Do not be alarmed if your tropicals stop growing or even drop leaves when they come indoors. Most tropicals have a natural dormant season in their native areas. Cold weather and fewer daylight hours may not be their normal stimulus, but changing seasons often triggers it anyway. Watch soil moisture levels, and keep pots clear of any falling leaves. Don’t force growth; breaking dormancy too soon can stress the tree long term.

1.11.7 Preparing Outdoor Trees For Winter

Gardening chores are not over just yet. A bit of extra work now can give your trees a good head start on next year. Remove ALL dead leaves, debris, and twigs lodged in branches or lying in the pots. These are where overwintering pest insects and disease spores hide. Top off the soil in the container with a thick layer of fresh pine bark soil conditioner or finely chopped pine mulch. This will insulate against temperature changes and reduce water loss from the exposed soil. It can be removed again at the start of next year’s growing season and replaced with normal soil.

If a tree had any significant insect damage this past summer, spray the tree with light horticultural oil (usually a citrus–based oil), or neem oil. This treatment helps reduce water loss from the bark, kills many disease spores, and smothers eggs & juvenile insects that overwinter in the cracks of the bark. Both types of oil work particularly well on soft–bodied sucking insects like aphids, whiteflies, scale, and mealybugs. They also are non–toxic to animals, so are safe around pets.

While you are at it, most outdoor trees can be given a preventive treatment with light horticultural oil (also called summer oil) twice each winter. The first treatment is applied when moving trees into winter storage. The second treatment should be in late winter, before the buds start to swell. Some people recommend heavier dormant oil but I do not like or use it. There are too many trees that do not tolerate it. If you decide to use dormant oil, wait until mid-winter and skip the light horticultural oil. Regardless of which type of oil you use, carefully read and follow the instructions on the bottle. Trees can be badly injured if either type of oil is mixed incorrectly or used out of proper season. Do NOT use dormant oil on conifers and evergreens.

1.11.8 Winter Storage

Cleaned and sprayed trees can be overwintered several ways. Evergreens are still actively photosynthesizing in winter, so will need some light. Deciduous trees do best here if kept in shade; this helps prevent their buds from breaking during that invariable warm snap we get in February, just before the March ice storms and late freezes. Keep in mind too that dry wind damages a tree more quickly than the cold. Provide trees with shelter from the wind.

One option is to keep trees in an unheated garage or shed that gets some natural light. Another option is to place the pots on the ground in a shady, protected area, then mound dry leaves or pine straw around them as insulation. A corral of chicken wire will help keep the pine straw or leaves in place.

Personally I create a tree corral with pieces of 4’x 8’ pressure-treated lattice. It provides more wind protection and keeps out marauding deer and rabbits. I put 3 stakes in the ground in a shaded spot, 3 feet apart then set a 4’ x 8’ lattice panel on its long edge, and wire it to the stakes to form one wall. Twelve feet away and parallel to the first panel, I stake up the second panel. Then I fill the ground space between the panel walls with trees and pots, and stuff freshly chopped leaves or pine straw in between pots and on top as insulation. When the area is full I wire the last 2 pieces of lattice to the ends to close the space off.

Be sure to leave the foliage of evergreens exposed to light; some authors recommend burying deciduous trees entirely in pine straw, but that is probably not necessary in our milder climate. Trees that have delicate branches should be protected from falling limbs or wind–blown debris. One good solution is to place them beneath a wooden picnic table, then drape the windward side of the table with clear plastic to block the wind.

Heeling in is another over-wintering method that is widely used to hold over fruit and ornamental trees that are not ready for planting. For each tree, dig a hole that is twice the size of the root ball, and half–fill it with black loam topsoil ($1.40 a bag at Lowe’s or Home Depot) or moist, well rotted leaves.Lift each tree from its pot, disturbing the roots as little as possible. Bury the entire root mass of each tree in the prepared hole, covering it with additional soil if needed. As before, shelter the tops of the trees from the wind with a tent of stakes and plastic, or a windbreak of willow fencing.

One final reminder. Plan ahead for how you will water the trees if needed. Even during winter, the trees need enough moisture to keep the roots alive. You might only need to water them three or four times this winter, but it will be quite a chore if the only convenient water spigot has been cut off and drained.

1.12 December

A Trident Maple (Acer buergerianum) bonsai on display at the National Bonsai & Penjing Museum at the United States National Arboretum. Photographed in December, it is easy to see the winter silhouette. Link to original image.

1.12.1 General Weather

This is when we settle into reliably cold weather. Once trees are packed away, most work with trees is done for the year. The latter half of December and January are a good time to: start planning for next year; order training pots, tools, wire, and other supplies; and building or refurbishing benches.

1.12.2 Pruning, Wiring and Grooming

Remove all wire from branches that have set, to lessen the chance of cold damage.

You should not be pruning branches, but it is a good time to start developing a pruning plan for deciduous trees that are in training. Start choosing the major branches you will remove from smaller trees. Get down on the ground and look at your field-grown trees from all sides. Are there branches that can come off? Mark them now using colored twist ties. Do the same with any trees in pots.

Also look at foliage pads on evergreens. Take photographs before storing trees, so you have a reminder to look at as you plan.