How to treat tree drought, save tree after heat damage

Q: It seems like everyone got a bunch of rain in the past couple of weeks except for us. We have not had a measureable rain in three weeks. Several of our trees are dropping leaves. They are turning yellow and falling off six weeks before they should be falling off. Should I be concerned? We are on a well, and we can’t water them as much as they need to be watered.

A: Hot, dry

weather happens somewhere every summer. The natural response for trees is to drop leaves they can’t support. If there was plenty of water in the spring, the trees would have grown leaves and roots in response to the plentiful amount of water available. Then, as the weather dries out, the trees respond by allowing roots and leaves to die.

The top and bottom of a tree maintain a balance. There won’t be more leaves than the roots can supply with water, and there won’t be more roots than the leaves can supply with food.

If the dry weather happens before midsummer, the trees may respond later in the summer by growing additional leaves. If the leaves fall off after midsummer, the tree will not need the leaves and will not regrow them until next spring.

Trees planted in the past few years should be watered to prevent the premature leaf fall.

Q: We had a brush-pile fire get out of control for a few minutes. It spread to some construction debris stored under some trees. The tree trunks were not burned. The leaves above the burned area were green for a few days but have since turned brown. The flames did not get to the leaves, but the heat did.

We have been advised to remove the trees or cut off the branches. That would leave a large, empty area in the woods. We don’t want to do that. How long should we wait to see if the tree branches are OK?

A: You will need to wait a few weeks at least. The brown leaves are dead, but they may not fall off the tree as they normally would because they are not going through the normal fall leaf-drop process. In the fall, trees take the nutrients from the leaves back into the branches. Then they form an abscission layer that walls off the leaf from the stem. The leaf then falls off.

The heat-damaged leaves are on branches that may also be heat-damaged. They may not form an abscission layer, so the leaves may remain on the tree into the winter.

The natural response for a tree that loses a bunch of leaves in the summer is to grow more leaves. This requires nutrients and water from the branches, trunk and roots. The fire may have damaged all three of those areas, but it will be difficult to figure out how much damage there is to those areas.

We are close enough to fall that you don’t really want the trees to send out new leaves now. The new leaves may not be on the tree long enough to replace all of the nutrients in the tree that are needed for their creation before the cold weather comes. If there are not enough sugars and starches replaced into the branches, the branches may not survive the winter. Plants use sugars as antifreeze to prevent the cells from freeze damage. The lack of nutrients may also not allow for many leaves next spring. The branches may look good this fall, but they may not come back out in the spring.

It would be best for the trees to wait until spring to grow new leaves, but it will be difficult for you to know if the tree branches are still alive until spring.