Japanese Maples Do Sunburn

Help for the Home Gardener from the
Contra Costa Master Gardeners' Help Desk

Japanese Maple leaf scorch...
picture: Missouri Botanical Garden

Client's Question:
The client has several young Japanese Maples suffering from sun burned and sun scorched leaves. They are concerned about the welfare of the trees and how much to water them. They were told by the nursery to water one gallon every three days.

Master Gardener Response:

Sun Burned/Scorched Leaves: You did not mention what type of sun exposure your maples have so I will address that first. Most Japanese Maples will do well in a location with direct morning sun and shade in the afternoon. Hot afternoon summer sun exposure on many varieties of red Japanese Maples can result in sun burned leaves. I can personally attest to this. With the recent summer winds and hot sun, all of my Japanese Maples have sun burned leaves and some early leaf drop. This often occurs in late August through September but has so far never affected the overall health of my trees.

Leaf scorch can appear on any type of deciduous tree, shrub or plant. During prolonged periods of drought, windy weather or bright sunshine, Japanese Maples are particularly susceptible, especially young trees. In hot weather with dry soil, tree roots cannot absorb enough water to send to the leaves. Foliage may stay on the tree in mild instances, but premature leaf drop occurs in severe cases of leaf scorch.

Watering Japanese Maples: Your question regarding a proper watering schedule is challenging because of several factors including your soil type and whether this is a newly planted or an established tree. Generally speaking, watering of Japanese Maples should be done uniformly throughout the growing season and even more during summer heat. Japanese Maple trees have fairly shallow roots that can dry out easily. Your Japanese Maple requires a consistent amount of water. The amount of water will also depend on your soil type. A clay soil will retain more moisture than a sandy soil. Your nursery's recommendations on watering may fall short in during a drought season, and especially in light of our summer's high temperatures and windy days.

The University of Colorado web site referenced below is a great resource on caring for trees in a drought year. However, a Japanese Maple is a moisture loving tree and if it is newly planted, will require additional monitoring and water. A three inch layer of mulch is helpful to provide moist conditions as well as winter protection for the shallow root system. Mulch will also help cool the soil in summer. Some other good cultural practices for your tree's health include keeping lawn 2-3 feet away from the trunk and keeping mulch about 6 inches from the trunk.

Some Additional References Worth Reviewing on Japanese Maple Care:

General Information on Tree Care in Lawns from the Contra Costa Master Gardeners
http://ccmg.ucanr.edu/files/177645.pdf

Information on Japanese Maples; Master Gardener Newspaper Articles
http://ucce.ucdavis.edu/files/datastore/268-223.pdf

University of Colorado resource for addressing water needs in a drought situation
http://www.colostate.edu/Depts/CoopExt/4DMG/Trees/caring.htm

Missouri Botanical Gardens on leaf scorch:
http://bit.ly/1l1N4r8

Contra Costa Master Gardeners' Help Desk

Editor's Note: The CCMG Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. (map) We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, and we are on the web at http://ccmg.ucanr.edu/. "Ask a Master Gardener" help tables are also present at many Farmers Markets as well as at the CCMG's "Our Garden" programs (map). See the CCMG web page for details/locations.