Chapter 101 Juniperus spp.
101.1 Junipers
Sargent juniper with a weathered, fissured trunk, in the Brooklyn Gardens collection. Link to original image
There are five species that are commonly used for bonsai. A sixth is not often used for bonsai, but is native to the eastern US.
| Species | Name | Native Region | Soil Mix | Light |
|---|---|---|---|---|
| Juniperus chinensis | Chinese or shimpaku juniper | China, Korea, Japan | lean mix | full sun |
| Juniperus communis | common juniper | boreal Northern hemisphere | lean mix | full sun |
| Juniperus conferta | shore juniper | sand dunes of Japan | lean mix | full sun |
| Juniperus procumbens | Ibuki juniper | Japan and Korea | lean or general deciduous mix | full sun |
| Juniperus rigida | temple juniper | northern China, Mongolia, Korea, Japan | lean mix | full sun |
| Juniperus virginiana var. virginiana | Eastern red cedar | eastern US | general deciduous | full sun |
101.2 Soil: General Deciduous / Rich Conifer Mix
Ratio: 3 parts bark, 1 part grit
Add-ins: dolomitic limestone (~5 lbs/yd), Tree-Tone (15 lbs/yd)
pH: ~6.5 (slightly below neutral)
Moisture: Average. Preferred by eastern red cedar and Ibuku juniper.
101.3 Soil: Lean Conifer Mix
Ratio: 2 parts bark, 1 part grit
Add-ins: dolomitic limestone (~5 lbs/yd); Tree-Tone (15 lbs/yd)
pH: ~6.5 (slightly below neutral)
Moisture: Fast draining
Best for junipers that are adapted to alpine or sandy conditions.
101.4 Light
Routine: full sun, including in summer.
101.5 Cultivation Notes
Each of the junipers behaves slightly differently, but the general training and management strategy is the same for all species.
101.5.0.1 More Suitable for Bonsai
Shimpaku junipers are one of the most popular species for bonsai. They are hardy, thrive in coastal conditions, and do well in hot sun and sandy fast-draining soils. The leaves grow in two forms, juvenile needle-like leaves that are 5–10 mm long, and adult scale-leaves that are 1.5–3 mm long. They also have rough, mature-looking bark even when young.
There are more than 100 named cultivars selected for various characteristics such as yellow foliage, or permanently juvenile foliage. Juniperus communis ‘Green Carpet’ is a prostrate shrub similar to J. procumbens.
Japanese needle pine in a slanting, driftwood style. Link to original image.
Shore junipers are specialized to grow in sand dunes and coastal areas. Some taxonomists categorize them as a subspecies of temple junipers. They also are used for bonsai, but are not as commonly available.
The temple juniper is native to northern and central China, Mongolia, Korea, northern Japan, and Russia. They are best adapted to low hills and mountain areas. Temple junipers are closely related to common junipers, which is a circumpolar species with an overlapping range. Temple
Ibuku junipers, also called procumbens junipers, are low growing natives of Japan. Several cultivars have been selected, the most widely grown being ‘Nana,’ a slow-growing form that is used frequently for bonsai. Like shimpaku junipers, they can have both scale-like and needle-like foliage.
A Juniperus procumbens ‘Nana’ in the Golden State Bonsai Federation Collection. It has been trained for 10 years, from a stock plant for cuttings at a nursery. Link to original image
101.5.0.2 Less Suitable for Bonsai
Common junipers vary greatly, ranging from low spreading shrubs to 30-foot trees. The needles emerge as bundles or whorls from the sides and tips of branches. There are several named cultivars, and some have been used for bonsai. I would not choose one for here simply because they are adapted for much cooler summers and colder winters than we have here.
Eastern red cedar is found in eastern North America, from Maine, west to southern Ontario and South Dakota, south to east-central Texas and the Gulf coast. Our native cedars are occasionally used for bonsai, but not nearly as often as the Asian natives listed above. They seem to be fussier about root and branch pruning, and less tolerant of poor soil.
Planted in open group, red cedar tolerates a wide range of soil types. It prefers moist soil but does not like to be wet for extended periods of time. They can also tolerate dry conditions. In bonsai pots, they seem to prefer slightly moister soil conditions than other junipers.
101.5.1 Potting & Root Pruning
Repot junipers in mid-spring. Lift trees free from their containers and look for new white roots emerging. If there are no white roots visible, it is too early. Wait another week and check again.
101.5.1.1 Top & Branch Management
Heavy pruning: cut major branches at the same time as repotting.
Fine pruning: finger pinch routinely during the growing season to maintain foliage pads.
101.5.2 Feeding
Fertilize junipers that were not repotted in spring when new growth appears, then every 2-4 weeks until October. Do not fertilize for 3-4 weeks after repotting.
Apply slow-release shrub and tree fertilizers at half the recommended rate. Alternatively, water with water soluble fertilizers at half strength rather than full strength. Use fertilizer formulated for acid-loving plants. An evergreen specific fertilizer such as Holly Tone is perfect.
101.5.3 Pests & Problems
Junipers in this area are very prone to spider mites. Look for tiny pale whitish spots on the needles. They are where mites have been feeding. Other signs are tiny red crawling dots, smaller than a grain of pepper. Tiny unevenly formed webs are another sign.
If you have crabapples in your bonsai collection or the landscape, be on the lookout for cedar apple rust. The spores spread in the air from apples to junipers and back. The “apples” that form on cedars actually are tumor-like growths in the stems and leaves. Eventually these will sprout orange jelly-like “horns” that scatter trillions of spores to the wind. If you find cedar apples, break the apple in half and peel it away from the stems. Throw the remains in the garbage, not the compost pile.
Chemical Warnings
Juniper foliage is sensitive to insecticidal soap and horticultural oils. When looking at chemical treatments, make sure the label says the compound is safe for junipers.
101.5.4 Winter Storage
Store in mulch outdoors. Try to place in a shaded area so buds do not break in a mid-winter warm spell. No other special precautions are needed.