Q. I have several Carolina Cherry Trees in my yard. Last year the leaves began turning brown and flake off. Can you tell me why they are doing this and how I can correct the problem?
|Carolina cherry laurel and leaf drop|
A. Let's get one thing out of the way before we begin. It is called Carolina Cherry Laurel for a reason. This plant is native to the humid, wet climate and rich soils of the southeastern United States. It is not native to dry, deserty climate and barren soils of the southwestern United States. It struggles here compared to the Southeast. This plant requires extra care on your part when growing it here.
|Carolina Cherry laurel and leaf scorch|
Add 50% decent compost to the soil mix when planting. Dig and amend a hole at least three times the width of the container. Five times is better. If this wasn’t done at the time of planting, make vertical “chimneys” 2 feet deep and 2 to 3 feet from the tree trunk. Fill these “chimneys” with compost or a 50% mixture of compost and soil.
|Cherry laurel heat or water stress|
Covering the soil with rock up to the trunk is a bad idea. It will work for a few years, until the soil amendment is gone, but eventually these plants will pay the price. No, I take that back, you will pay the price. Plants that begin their name with “Carolina” or “Japanese” are going to struggle in our Mojave Desert environment.
|Once in awhile someone puts it in the right location and adds enough soil amendments at planting. But it will go down with all that rock mulch around it unless compost is added regularly and watered in.|
This doesn’t mean, “Don’t plant them!”. It means be careful where in your landscape you place them and how you grow them. Plants that do not belong in the desert require more investment at planting, long-term care and money to grow them here than in their native habitat.
After planting them in a 50% mixture of compost and soil, cover the soil beneath their canopy with wood chips 3 to 4 inches deep. Woodchips should cover an area at least equal to the canopy spread of the plant. This surface “mulch” will need a couple of inches of new mulch on top of it every three years or so. This is because the bottom layer “dissolves” or rots into wet soil beneath it over time.
This rotting of wood chips enriches the soil it touches and adds nutrients and biological activity to it. These are important ingredients to the long-term success of “alien” plants growing in our desert environment.
The discoloration and death along the margins of the leaves arises from a plant health problem. Improve the health of these plants and they will be more tolerant of our desert conditions. Additions of compost and woodchip mulch to the soil surface will help.
Make sure that these plants are getting enough water from at least four locations around the trunk. These emitters should be about 18 inches from the trunk in a square pattern with the trunk at the center. They should be giving these plants enough water at each irrigation. If these are drip emitters, they should be emitting water for enough minutes to allow it to drain 18 inches deep. Depending on the emitters, this could be 30 minutes to an hour.
Irrigation of large trees and shrubs should never be daily. Give large plants at least one day without irrigation so that water can drain from the soil and the roots can “breathe”. The roots of these plants are very susceptible to suffocation, root rot, when soils remain wet and cannot drain adequately.
The major problems with this plant, because it is so closely related to plums and peaches, are many of the same problems as fruit trees. When I look closely at the pictures you sent, which are very good and thank you very much, I see root weevil damage on the leaf edges. These are the notches that you see on the margins. These insects feed at night and are in the soil beneath the plant. There is not much you can do about them except perhaps apply a systemic insecticide around the roots after the plant has finished blooming. Use the Bayer insecticide if you go down this route.
I believe if these plants were in good health you would see little to none of this type of damage. I believe the plants would be very full and the leaves would appear healthy. Make sure you apply either wood chip mulch around the trees as I suggested earlier and combine that with a yearly application of a tree/shrub fertilizer in late January or early February. Only use mineral fertilizers if you have wood chip mulch surrounding the trees. Again, I repeat. This should not be bark mulch if you want to improve plant health.
Don't get me wrong. There is nothing wrong with bark mulch. It can be very beautiful but it adds nothing to the health of the plants. It is purely decorative. Wood chip mulch, trees and shrubs that are shredded in their entirety and applied to the soil surface, improve plant health when they begin to break down/decompose a.k.a. "melt" or "dissolve" back into the soil.
Another problem with this plant is a plant disease called shot hole fungus. We see this leaf disease on peaches and plums when our humidity is too high. In climates with higher humidity, like some of those in California, this disease can be a severe problem. In fact, varieties of peaches and plums are grown in certain areas with high humidity strictly because of this disease problem. This disease causes spotting on the leaves and sometimes the leaf margins. As this disease worsens, sections inside of the spots die and drop from the leaf leaving "shot holes". Some varieties of plants are much higher susceptible than others. If the health of the plant is improved, I am guessing this disease will disappear or minimized.Bottom line. Improve the soil and drainage. You can do this by drilling holes in the soil with an auger as deep as possible. Fill these holes as best you can with compost. This will improve the soil and improve drainage. Cover the soil with wood chip mulch at least 3 to 4 inches deep. Fertilize with compost this year and next year you can use a mineral fertilizer if you wish provided wood chip mulch has been on the surface of the soil for 12 months. Avoid daily irrigations.