Ask the Master Gardeners: Placement and proper watering important to keep Japanese maples healthy through heat of summer

By: Laurie Meyerpeter, Placer County Master Gardener
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Question: I just bought a Japanese maple from a nursery. The nursery said it is a sun-tolerant variety but when I planted it in my yard last July, in an area that gets full sun, it got severely burned. Why? Answer: Japanese maples are very sensitive to heat, strong sunlight and low humidity levels — all common in this area. Some Japanese maples are more tolerant of strong sun than others, but “sun tolerant” does not mean “I love baking hot sun in the Mojave Desert.” It merely means that the tree tolerates more sun than other Japanese maples. Japanese maples prefer to grow in either morning sun or filtered light. Sun tolerant varieties will survive in stronger sun, but still prefer to be sheltered from intense afternoon rays. Japanese maples grown in a nursery were probably not growing in full sun there. Suddenly moving a plant that has been growing in shade, partial shade, or part-day sun in a nursery setting into a full-sun location subjects the leaves to much more sun than they are accustomed to. It is like going to the beach the first sunny day of summer after wearing layers of clothing all winter. Your pale winter skin burns quickly until it becomes accustomed to greater amounts of sun. Leaves are similar and burn quickly when exposed to more sun than they are accustomed to. Most importantly, summer is the worst time to plant trees. Long hot days are very stressful on trees and when planted in summer, the roots don’t have time to grow out into the surrounding soil and absorb moisture at the very time of the year that a plant needs water the most. Autumn is the best time to plant, with spring a close second. Right now, pay attention to watering practices. Water deeply and as often as needed to keep the soil moist, but be careful not to over-water. The soil should be moist, not soggy. Apply several inches of mulch to slow moisture loss and keep the soil cooler. Do not remove dry leaves as they will shade the trunk and branches. Each year as the tree’s roots develop, the plant will be better able to sustain itself through our long, hot, dry summers. Eventually, the maple should mature into a lovely garden specimen.