Toronto Master Gardener Factsheet    

Did you know?

There are many cultivars of Japanese maple, most of which grow only in Japan and surrounding areas. This Factsheet deals with the ornamental trees that are hardy in North America. Acer palmatum and A. japonicum include 250 cultivars which have been bred, selected and propagated for over 300 years by the Japanese.

Japanese maples may grow 15' to 25' in height, but some are much smaller and tend to mound after 6'. They have a medium rate of growth when young, slowing down to become a slow grower - 10' over a 10-year period. The leaves are green in summer, turning yellow, bronze, purple or red in fall. They will hold leaves until late November.

How to grow them

Japanese maples are very easy to plant. The fibrous root system is not deep, but will stay in the upper level of the soil. Japanese maples do well in containers of all sizes. Plant in partial shade; complete sun or deep shade alters the beautiful colours.

The best soil for Japanese maples is a sandy loam with a low to medium amount of organic matter, well-drained, and well-mulched if in adverse soil conditions. Additions of acid fertilizers are needed in extreme alkaline conditions. Japanese maples have the same soil pH requirements as rhododendrons.

Japanese maples should have a uniform supply of moisture. Proper water management is far more important than fertilizer or soil types.

Top shaping and pruning should be started rather early in the tree's life. Major pruning is done during the dormant season, corrective pruning at any other time.

Common problems

Insects:

Japanese maples are not often subject to serious insect infestations. Other than the usual range of insects found in landscapes, there are no major predators on these plants. Some problems are aphids, mites, moth larvae and root weevils. None of these is considered life-threatening.

Twig die-back:

This is the worst problem of maples. It can be caused by one or more of several organisms, cultural practices, climatic conditions or soil chemistry. The main cause of die-back is verticillium wilt. This is a fungus that enters the cambium layer, blocks the flow of nutrients within the tissues, and causes a brown streaking within the layers under the bark. New shoots, twigs, and branches will die quickly. No definitive solutions are available at this time. It is important to sterilize all pruning equipment during propagation, keep the tree healthy, and remove infected parts which are then burned. This will limit further spread.

Leaf scorch and twig burn:

There may be one of many causes: wind burn, exposure to extremely hot sun, late spring frost, salt runoff from roadways or excessively alkaline soils, short intense drought periods, container plants in full hot sun soaked during the heat of the day Usually the plant is not lost, but the appearance and vigour of the maple is damaged for that season.

Root rot:

This is caused by too much water, poor drainage, poor air circulation and insufficient light. Corrective action is the best remedy.

Propagation

Japanese maples are produced primarily from seed and by grafting. Commercial growers propagate by grafting named cultivars onto A. palmatum understock.

Read more about Japanese Maples

Vertrees, J. D., Japanese Maples, Portland, Oregon: Timber Press, 1987.

 

Factsheets are produced by the Toronto Master Gardeners in association with the Toronto Botanical Garden. They provide introductory information about a broad range of horticultural topics and are intended for personal use and study purposes. Should your gardening group or organization wish to use multiple copies we ask that you inform the Toronto Botanical Garden at info@torontobotanicalgarden.ca.

Date revised: This factsheet was created prior to May 2005.