Chapter 72 Acer rubrum
72.2 Soil: Moist Deciduous Mix
Ratio: 4 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
Riparian and moist woodland species (red and Japanese maples, hornbeams).
72.3 Light
Routine: half-day to full sun.
Summer: mid-day shade.
72.4 Cultivation Notes
Red maples can be handled in much the same way as trident maples, though I would not root prune them as aggressively. Maples are among the first trees to break buds in early spring. New shoots extend quickly during spring, slow down once daytime temperatures reach the mid-80s.
72.4.1 Potting
Repot in early spring, just before or as the buds break.
72.4.2 Pruning
Red maples that have well-established root systems, can tolerate extremely agressive top pruning. If a 15-foot tree with a 3-inch diameter trunk (wrist-sized) is cut off 6 inches from the ground in late winter, it usually will have a dozen or more new shoots emerging from the cut end within a month. By mid-summer the longest shoots may be 6 feet or longer.
Make major branch pruning cuts in late winter to minimize loss of nutrients caused by removing a branch full of tree sap. Branch cuts may bleed for 1-3 days if the sap is already moving up from the roots. There is no need to seal pruning wounds, because with a little encouragement, maples fully close over most pruning scars.
Like trident maples, red maples respond well to a grow-clip-regrow-repeat approach. The new green shoots will extend quickly in the early spring. Remove small shoots that are not placed correctly to form scaffold branches. Let shoots being developed into new branches extend as much as they can until July, then cut them back to 1-2 pairs of leaves; the buds at the bases of the leaves will provide the next pair of extension shoots, either later in the year or the next spring.
In subsequent seasons, the lateral branches emerging from the primary scaffold branches can be pruned all summer.
Random green shoots will pop out all summer long. Clip them off with scissors at 1-2 pairs of leaves if they are in a place you want to keep them. I stop pruning in early September so I do not encourage late growth that will not be hardened by mid-November (our first hard freeze date).
72.4.3 Feeding
Red maples grow quickly so can be fertilized more heavily. Fertilize trident maples in spring, after new leaves have begun to emerge. Use slow-release fertilizers that have about three times more nitrogen than phosphorous. To feed more, don’t go up on the concentration of minerals; increase the frequency of feeding.
Good options:
- Slow release shrub and tree fertilizer, applied at half the recommended rate.
- Organic liquid plant food that must be broken down by soil microbes, such as fish emulsion.
- Inorganic, water soluble fertilizers at half strength rather than full strength.
72.4.4 Pests & Problems
I have not had any problems with pests on red maples.
Chemical Warnings
72.4.5 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.
72.5 Propagation Notes
Direct seeding is not a particularly good way to cultivate red maple, because their first year survival is low; one study of open ground seeding found that just 37% of seeds that germinated survived through their first year. More seedlings survived if seeded in tubes or 3-inch pots.
Red maples are extremely common in our area. Rather than try to grow them from seed, it is easier to collect seedlings as they emerge in early spring. Larger trees can be collected by root pruning in the ground in fall, then lifting them in spring.
72.6 Artistic & Styling Notes
Arthur Joura of the NC Arboretum has done a great deal of work with red maples, and found that they can be trained in the same styles as trident maples.
72.7 Additional Information
72.7.1 Natural History
Red maple is one of the most abundant and widespread trees in eastern North America, found from southern Newfoundland to Florida, and west to Ontario, eastern Texas and Oklahoma, and Illinois.
Red maple is a subclimax species that replaces pines during succession, then in turn are replaced by oaks and hickories.
Red maples develop best on moderately well-drained, moist sites, but they can grow on a variety of sites, from dry ridges to peat bogs and swamps. They tend to develop root systems that are adapted to the soil conditions. On wet sites, red maple seedlings produce short taproots with long, well developed laterals. On dry sites, they develop long taproots with much shorter laterals.
72.7.2 In Cultivation
Many cultivars are available to the nursery trade. Large trees from garden centers can be cut back and root pruned to convert them from landscaping stock to bonsai in training.