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Monday, July 10, 2017

African Sumac Yellow Leaves and Leaf Drop

Q.  Here are the rest of the photos of our African sumacs with leaf drop.  Our yard is too small for me to get far enough away to get an entire tree in the photo.  Please let me know if that would help and I’ll go outside the neighborhood wall and see if I can get a photo of the entire top of the trees.  Thank you for any advice you can give us!

Readers African sumac yellowing and dropping leaves

A. The usual problem with African sumac yellowing and leaf drop this time of year is a lack of water. When these trees are planted by landscapers they frequently do not use enough drip emitters. Or when they plant them small, they use just a few emitters and no one adds more emitters as these trees get larger. During hot weather the amount of water larger trees require is considerably more than when it was growing during 90° weather. It is now 115 to 117F. And it has been very windy.

Another possibility could be watering too often. If the tree roots are in soil that is watered daily and it's not draining, the roots could suffocate. If they begin to suffocate and die they can also have yellow leaves and leaf drop. I think this possibility is less likely in your case.

There is a 3rd possibility. It is possible to water these trees daily and still not give them enough water. If the total volume of water applied is not enough to satisfy the trees demand for water, they can actually be under watered even when they are watered daily. I would add more emitters instead of increasing the number of minutes on the controller. Yes, I know it's more work but you won't be over watering everything else on that valve.

There is one way to find out. See if the soil around the tree is wet or dry. Take a steel probe that is at least 18 inches long. This can be a very long but skinny screwdriver or it can be a piece of 3/8 inch steel rebar 3 feet long. 
This screwdriver might work if it is long enough.

Push it into the soil in several locations under the canopy of the tree. If it pushes into the soil with a great deal of difficulty, then the soil is too dry. If this is the case, flood the soil under the tree with a hose or sprinkler with a good soaking that goes down at least 18 inches deep. You have the probe so you can measure how deep the water penetrates by pushing the probe in the soil. If the water is running off of the area, turn the sprinkler or hose on multiple times 30 minutes or an hour apart. I use a mechanical water timer and an inexpensive sprinkler on the end of a hose. You should see a response by the tree if the soil is dry in 7 to 14 days.
It would be like this but there would be no grass.
If the soil is too wet under the tree then of course you have to wait longer between waterings. But I tend to think it's probably not getting enough water. Covering the area of the soil under the canopy of the tree with woodchip mulch 4 inches deep helps keep the soil wet tremendously.

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