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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.
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