Ask the Master Gardeners: Insufficient water is likely the problem behind Japanese maple ‘sunburned leaves’

By: Laurie Meyerpeter, UCCE Placer County Master Gardener
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Q: My Japanese maple is getting sunburned. The leaf edges are turning brown. How can I prevent this? A: Although frequently dubbed “sunburned leaves,” dry leaves on Japanese maples are more commonly a water deficit problem. “Sunburned” leaves commonly discolor and dry out in the center of the leaf on areas of the tree receiving the greatest amount of sun, while lack of sufficient water usually causes the tips and edges of the leaf the dry out. Sometimes both happen on the same plant but, more commonly, the plant isn’t getting enough water. Of course, sun is a major factor. Causes of insufficient water reaching the leaves include too much sun, high temperatures, dry air, hot winds, not enough water (or water that does not soak into the soil or runs off) and an immature root system. The first step to preventing dry, crispy leaves involves choosing the right tree and planting it in the right location. Most nurseries will assist gardeners in choosing a tree that will do well in a chosen site. If planting in a sunny location, remember that “sun tolerant” does not mean “I love baking hot sun in the Mojave Desert.” It means the tree tolerates more sun than other Japanese maples. Gardeners should plant the tree in either the fall or early spring to allow the tree to develop a more extensive root system before summer, which will enable the tree to pull up more moisture from the soil when temperatures heat up. If possible, plant the tree where it is not subjected to hot afternoon sun. If the tree is already planted in direct afternoon sun, expect crinkly leaves for several years until the tree has developed adequate root growth and pay close attention to watering practices. Water often enough to keep the soil slightly moist and deeply enough so that the roots are encouraged to grow deeply. Don’t water the tree so often that the soil is constantly saturated. Over watering is a leading cause of Japanese maple death. Apply a 3-inch layer of mulch to conserve water moisture in the soil. (Pull the mulch away from direct contact with the trunk.) Given proper conditions, a Japanese maple should exhibit fewer and fewer dry leaves as it matures and grows into a lovely addition to a garden.