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How Summer Heat Stress Affects Your Trees

by Keith Brown
July 30, 2009

Summer heat stress is one of the number one tree killers I run into. Okay, realistically no tree ever dies from just one problem, but rather a cumulative affect of many stress factors. Heat and drought stress are stress factor that almost all trees in the central Texas area deal with on an annual basis. So, if your tree has some other factor stressing it out, the summer heat might be the straw that breaks the camel’s back. I see more trees die during the summer time than any other time of the year.

Crepe Myrtle with droopy leaves

Crepe Myrtle with droopy leaves

Some trees suffer from heat stress more than others. For example, live oaks and cedar elms cope very well; sycamores and cottonwoods with will begin shedding leaves with moderate heat levels if water is scarce.

One important factor to consider when trying to quantify damage from heat stress is to take note of the date when your tree loses all its leaves. My experience has been that if a tree can hold its foliage through July into August then it will usually leaf out full the following spring. In some cases the tree will even put on a new set of foliage in September to effectively produce more sugars for itself through the fall growing season. Worst case scenario is if your tree succumbs to a heat wave in the spring. We’ll often get a hot spell in April or May that will reach 100F. If your tree loses all its leaves this early it probably won’t bounce back.

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Be sure to post a photo if you want some advice on your tree.

  • EB says:

    I’ve got a bunch of live oaks and cedar elms that are yellowing out now in the middle of August as we plod along in this heat wave. Is there anytthing I can or should do about it? Should I water? If so, how much? Should I let them go dormant (if that’s what they’re doing)? Pleaes help. I love my trees and I’d like to keep them. Thanks.

    -EB

    • Keith says:

      It’s pretty normal for trees to drop foliage early during hot, dry years. The leaves turning yellow before they fall is an indication that they are going through a normal senescence process. Worst case scenario is if the leaves turn brown and don’t fall off. It’s more common for the elms to drop early than the live oaks. A healthy live oak will typically deal with summer heat stress very well. There is probably some other underlying factor adding to their stress. A deep watering once a week will go a long way. It probably won’t stop the leaf drop, but it will reduce the stress on the trees and help them rebound next year. You should have your trees looked at.

  • Peter Ramos says:

    I have a post oak which a few days ago started turning yellow, and then brown, then dropping leaves. Seems to be most pronounced on one side and from bottom up (top still seems relitively green and healthy. I have been watering the lawn around tree every other day. Prior to the last few weeks which have been 95-100 degrees, we have had a relatively wet summer (for Texas). I do not water directly on trunk either. Any thoughts or advice?

    • Keith says:

      Trees have a delayed response, so stress from the last two years of drought carries over to this year. I’m expecting next year to be rough, too. If you still have foliage at the top you are in good shape. Post oaks are very sensitive trees, if it starts going down hill, you might be in trouble. Can you post some pictures?

  • Mark says:

    I have a Texas Red Oak that we planted in late February this year going through heat stress this year. It’s leaves are turning brown. It’s due to the ridiculous heat wave we got this year. My Chikapin did the same last year. We have been watering it, but not sure what to do. Is it going to bounce back like my Chikapin or should I be concerned?

  • DB says:

    Despite regular watering, the leaves on the Mexican Sycamore I planted this winter are starting to turn brown, and some are dropping. The Monterrey Oaks and Texas Red Oak planted at the same time are doing well. Is there anything I can do other than continuing to water and hope for the best?

  • Diana says:

    I have a tree the electric company cut the back half of last spring (completely unnecessary). This year, with the heat wave, very large limbs are just breaking off. I’m worried that I’m going to have to cut this whole tree down, but I still see new growth and new leaves on the side the electric company mutilated last year. Is there any hope?

  • sandy says:

    I planted a Japanese red maple this year at the end of June. It was in a container but wrapped in burlap. It is mostly in shade and I am watering – but how much does it need in this heat? It is about 2 inches in diameter. Thanks

  • DB says:

    Despite my best efforts, the Mexican Sycamore I planted in the winter of 2010-11 seems to have died. ( My Monterrey and Texas Red Oaks planted at the same time have survived nicely.) However, I notice a couple of suckers or sprouts have sprung up. So, I assume the root system still lives. What next? Give the sprouts a chance or remove it all and replace with another tree this coming winter?

    Thanks