Growing Japanese Maples: A Toronto Master Gardeners Guide

 

A mature Acer palmatum ‘Bloodgood’ Japanese maple catches the sunlight. (Photo: Helen Battersby)

Did you know?

There are many cultivars of Japanese maple, most of which grow only in Japan and surrounding areas. This gardeningguides deals with those 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 over a 10-year period. The leaves are usually green in summer, although some have red or mottled leaves. In the fall, the leaves turn 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 appropriate 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. If you amend the pH, be aware that this will be required every few years.

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 early in the tree’s life. Major pruning is done during the dormant season, corrective pruning at any other time.

The red-trimmed foliage of Acer shirasawanum ‘Aureum’ (syn. Acer japonicum ‘Aureum’), the full-moon maple. (Photo: Helen Battersby)

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 most serious 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, 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 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. 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.

Japanese maples come in an array of leaf forms. Here, the fine foliage of a red Acer palmatum dissectum. (Photo: Helen Battersby)

Propagation

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

References

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

Date revised: created prior to May 2005.

For printable version, click:  Growing Japanese Maples – A Toronto Master Gardeners Guide

 

Produced by the Toronto Master Gardeners, these Gardening Guides provide introductory information on a variety of gardening topics.

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