Ornamental or flowering plum leaves with wind damage

Q. I put in a desert landscape with 2″ of rock in the front yard with various bushes and 2 flowering plum trees. This probably was a mistake, as I read one of your articles which said that this type of tree is not suited for rock mulch. Anyway, my question is about watering the trees. I have a 28″ diameter by 5″ deep watering reservoir around each tree. There is a layer of bark mulch in the reservoir. Right now I water the trees twice a week filling the reservoir up twice at each watering.

This is purple leaf plum in a desert or rock landscape. It will look good for about five years without much attention. But after about five years it usually starts with leaf scorch and may begin getting iron chlorosis

So far every summer around August some of the leaves partially dry out and turn brown. Is this caused by too much water or not enough? I water the bushes 3 times a week by drip system for 30 min per watering. They are all healthy and green. Also the bark on the trees are splitting in places and falling off. Do you think I will loose the trees at some point? Any advice will be greatly appreciated. I read all your colums in the RJ that you write. Lots of excellent advice there.

A. Flowering plums can handle the rock better because you aren’t really worried about a crop of fruit to eat. But the rock on top of the soil will aid in the depletion of organic matter and over time it will most likely turn the pinkish color that accompanies iron chlorosis in red leaved trees like the purple leaf plum. If not corrected that can lead to more of a decline in the tree opening it for dieback and insect/disease problems.

This is the purple leaf flowering plum when it has iron chlorosis. Plants with green leaves will have their leaves yellowing with green veins. In plants with purple leaves the leaves will turn pink instead of yellow but the veins will still be a darker color than the leaf blade

Bark mulch is not nearly as effective as plain old ugly mulch made from chipped landscape trees. Not many nutrients in bark, it decomposes slowly, and is all just about the same size so it doesn’t decompose as effectively as chipped wood mulch. Plus 28 inch diameter irrigation basin is not very big. As these trees get bigger they will need more water. Increase the basin to about six feet in diameter (three feet from the trunk) all the way around the tree and fill this basin which should be about three to four inches deep. Fill it twice with each irrigation.

Hard to say why the bark is splitting and falling off but I would pull the loose bark off and look for damage to the trunk such as holes for borers. The bark should be removed anyway of the trunk is dead under the bark and it is pulling away from the trunk. Often this type of situation turns into a long lingering death spiral for the tree over the next few years when it will decline more.