During severe heat, with temperatures regularly reaching over 100-degree Fahrenheit, don’t forget that your trees need water and can show signs of heat stress during this drought-inducing weather. Trees signal drought stress with several symptoms, starting with foliage turning from dark green to light green, then browning at the leaf margins, wilting, and eventually prematurely dropping its leaves. During high temperatures, healthy trees can drop a significant portion of its leaves to conserve moisture. This usually doesn’t kill the tree, but can hold it back for a while until it recovers.
What about my Evergreen?
Evergreen is a bit of a misleading term because even evergreen plants have to shed older leaves and needles, the same way you have hair on your head all the time, but still lose hair every day. Healthy trees can regularly drop up to 10% of their existing leaves during a drought as a way to conserve moisture and maintain health. If they didn’t drop these leaves, they would lose too much moisture through transpiration, effectively a breathing process that takes place in the leaves.
Continue to follow our watering guidelines for newly planted trees and remember your established trees, as well. They need some extra relief from the heat. Download our guide HERE.
Fannin also recommends you start spraying the entire tree canopy a few times a week for 30 minutes either in the early morning or the late evening during 100-degrees weather to help the tree get a break from the heat. It will also knock off any dead leaves or small limbs and reduce the stress. An oscillating sprinkler with an adjustable spray that goes back and forth to cover the entire tree canopy will be helpful in this endeavor. Stay on track with your fertilizing schedule and increase your SUPERthrive treatment to every other week if your tree shows signs of stress for at least two months.
Signs of Drought Stress in Trees
Signs of drought will be most visible in the foliage of trees. Look for the following symptoms in times of short-term drought:
- Temporary Wilting: Wilting and drooping leaves will occur during the day. Leaves will recover and appear normal by morning.
- Permanent Wilting: As droughts progress, leaves will remain wilted even in the early morning.
- Yellowing Leaves: Before dropping foliage, leaves will turn yellow and exhibit fall color (Figure 1).
- Leaf Scorch: Leaf margins will have a brown or burned appearance (Figure 2).
- Defoliating Trees: Trees will generally begin to lose their leaves from the top and branch ends (Figure 3).
- Bark Cracks: During prolonged droughts, trees might develop longitudinal cracks in the bark, especially in thin-barked species like maples (Figure 4).
Figure 1: Chlorotic or yellowing leaves
Figure 2: Leaf Scorch
Figure 3: Tree defoliating from the top and branch extremities
