Japanese maple

About Japanese maple

Japanese maple is a small, slow-growing tree from Japan and Korea, loved for its finely lobed or lacy leaves in green, red, purple or gold and its bright fall color. Cultivars run from knee-high weeping mounds to 25-foot trees, and many have colorful twigs for winter. It self-sows easily and is listed as invasive in Virginia and Washington, DC.

Zones 5-8 (Morton Arboretum); not every cultivar is fully hardy in zone 5, and late spring frosts can burn new leaves. Invasive: it self-seeds and the Mid-Atlantic Pest Council lists it as invasive in Virginia and DC (NC State).

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

Plant container or balled-and-burlapped trees. Container trees can go in any time the ground can be worked, but fall is the best season in the South because roots keep growing through mild weather (Clemson). Dig the hole no deeper than the root ball and at least twice as wide, keep the top roots level with the soil, and mulch 2-4 inches without touching the trunk. Pick a spot with morning sun and afternoon shade, sheltered from drying wind. Most cultivars are grafted (NC State). Don't prune in spring, when maples bleed sap heavily (Morton Arboretum).

Soil

Evenly moist, well-drained, acidic soil rich in organic matter; it tolerates alkaline soil but not drought, and dry, sunny or windy spots scorch the leaves (NC State, Morton Arboretum).

Test the soil first. Loosen a wide planting area and mix 10-20 percent compost into the native soil you dig out; don't use uncomposted bark, and don't dig deeper than the root ball (Clemson). Aim for acidic, evenly moist soil rich in organic matter.

Feeding

• Spring to early summer, after the tree is established, and only if a soil test or pale leaves and weak twig growth show a need: slow-release nitrogen fertilizer with a ratio near 3-1-1 or 3-1-2 (3-0-1 or 3-0-2 if the soil test shows enough phosphorus). Spread it evenly from just outside the trunk flare to the dripline and water it in. Clemson cites 2-4 lb of slow-release nitrogen per 1,000 sq ft per year, split into a spring and a late-summer feeding; follow your soil test.
• Late summer to early fall, the second half of the year's split feeding (only if a soil test calls for it): slow-release nitrogen fertilizer, same as spring. Apply the rest of the year's amount over the root zone and water in. Don't feed a drought-stressed tree in summer (Clemson).

First-year watering matters far more than fertilizer: water daily for the first 1-2 weeks, every 2-3 days until week 12, then weekly, using about 1-1.5 gallons per inch of trunk diameter, until the tree is established, roughly 1.5 years per inch of trunk (UMN). Don't count on rain unless it was over an inch. Don't prune in spring, when maples bleed sap (Morton Arboretum), and don't let the soil dry out: drought and hot sun scorch the leaves. Too much fertilizer can burn roots and push soft growth that pests and cold injure (Clemson).

Varieties (16)

Pests to watch for

Aphids, Scale insects, Leafhoppers, Asian longhorned beetle

Diseases and problems

Anthracnose, Verticillium wilt, Leaf scorch, Frost injury, Drought stress, Mechanical damage (mower, trimmer and tie wounds)

In the kitchen

Pets: Not on the ASPCA's toxic plant list for dogs. The ASPCA's maple warning is for red maple, whose wilted leaves poison horses.