HEAT STRESS

When the weather is hot, maples in small pots are likely to show signs of heat stress, namely brown leaf tips and edges. The soil heats up quickly in small pots, making the roots unable to deliver water to the leaves, even though the tree is watered. As a temporary condition, this is in no way life-threatening. Just pot the tree into a gallon or larger pot or plant it in the ground. Give it a dose of fertilizer and keep the soil evenly moist. (You'd want to do these things whether the tree was heat-stressed or not.) Morning sun or dappled shade and protection from hot afternoon sun is the best exposure. The fertilizer should include some nitrogen (first number). In a few weeks, new normal growth should appear. In the fall, the tree will lose all its leaves, and next spring it will leaf out beautifully, with no ill effects from the heat stress. To avoid the problem in the future, keep the soil cool and evenly moist, avoiding wet/dry swings. Avoid dark-colored pots, which heat up quickly, and make sure the pot is larger than the tree's root ball. If the tree is planted in the ground, make sure it has protection from hot afternoon sun. A mulch at the base of the tree (rocks, bark dust, whatever) helps the soil retain moisture. If you water during the day, be sure to aim the water at the base of the tree, not at the leaves. Watering is best done in the evening or early morning.