Taking Care of Flash-Dried Trees

The triple digit extreme heat wave in early July resulted in flash drying many tree and shrub leaves, especially the newer growth.

Another heat wave is anticipated for late July, with the potential for several more before we cool down in November. To help your trees and shrubs cope, the magic ingredients are water and mulch.

Slow, deep watering that moistens the soil down around 6 inches is the key. Soaker hoses started at dinner time and left to drip overnight work pretty well. Be sure NOT to let the water hit the trunks directly as this sets the stage for a variety of root rots. If your trees are on a slope, arrange the soaker hoses in a “smile” on the downslope, starting about 3 feet away from the trunk. Best to do this every 3 weeks or so, but if we get another super intense heat wave, every 2 weeks will help. You can move the soaker hose to water a slightly different portion of the area under the dripline of the canopy each time.

And then there is mulch! Even on slopes, composted tree mulch, all the fallen leaves that are coming off the trees are super helpful. Not only does the mulch layer protect the soil from the strong heat and reduce soil temperatures, it also prevents evaporation of all the water you are adding. Last but definitely not least, mulch is a perfect home for many of the beneficial fungi, bacteria, and insects (the ecological FBI), that can help your tree defend itself from the disease-causing FBI.

A beautifully cared for purple hydrangea bush reveals singed leaves despite efforts of its owner to protect it with a beach umbrella. Photo by Bonnie Morgan

Now is NOT the time to do any heavy pruning. The leaves of the trees make the food for the tree. Removing green leaves is like taking the food factory away. While trees routinely handle this kind of stress, all pruning causes some weakening as the tree adjusts.
No need to add to the stress of incredible heat! The tension of the water within the trees when it is hot is incredible and cutting off branches can result in breaking this tension, kind of like snapping a rubber band. It takes a lot of energy and time to restore flow, so avoiding stressing the trees this way is critical.

Our trees have had a rough six years with the ongoing drought, and the rains are still months away. If we provide some water and mulch now, we can help support them through these dry times.


By Rosi Dagit


  1. Thank you, Rosi, for this critical information, especially regarding trimming out the scorched leaves. It’s not a pretty sight, but the protection these sunburned leaves provide for the rest of the leaving tree is obviously essential. I am concerned about our large sycamores as they appear to be losing all of their leaves, and we are not seeing any new green growth. Will they be as resilient as the oaks? With drip irrigation as you suggest? Do they need more/longer drip irrigation? Thanks, again.

    Susan & Arthur

  2. Thanks for this info Rosi.

    We have a lot of flash dried tree leaves and plants!

    Let’s hope for some rain – soon!

    All the best,


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