Leaves Yellowing and Burning Up

Q. What’s wrong with my plants? The leaves are all yellow and starting to burn up.

Readers plants are yellowing and looking pretty ugly because of rock mulch and some poor pruning practices.

A. I couldn’t see exactly from your pictures, but the plants appear to be either Photinia or Mock Orange. Regardless, I bet they were planted about five years ago and the soil was covered with rock. Desert landscaping without using desert plants. That leads to problems in a few years.

Yellowing of Photinia in desert soils because of rock mulch

            Mock orange originally came out of Japan and Korea and the Photinia came out of non-desert areas in China. However, both plants are very adaptable to different climates and that’s a reason why they are used in many places including here. I have had several people ask me which landscape plants are desert or desert adapted and which aren’t. I will put together a list and put it on my blog.

Bottlebrush yellowing because of rock mulch

            However, non-desert plants will struggle in desert soils, so the soils need to be improved at planting and under constant improvement as these plants get older. Yes, they look good for about five years after planted in amended desert soil but when they are incorporated into desert landscaping, surrounded by rock and not maintained properly, they don’t do as well when the organics eventually disappear from the soil.

Mock orange yellowing because of rock mulch

            The cause of the yellowing is a combination of soil reverting to its desert chemistry and suffocation of plant roots. Amended desert soil but covered in rock becomes a desert soil again in three to five years. The time difference, I think, depends on how much amendment was added to the soil and what kind was used. Unless you plant desert plants in desert landscapes and cover the soil and rock mulch, many start to decline in a few years. Photinia and mock orange are two that will.

What to do? 

You can try the Band-Aid approaches and spray them with iron foliar fertilizers multiple times each year. You can apply iron chelate fertilizer, called iron EDDHA in January of each year. You can spread some sulfur soil amendment and see if you can adjust the soil alkalinity so the iron already in the soil is available to the plants. Or you can replace these yellow plants with desert plants that can tolerate desert soils, our climate and the rock mulch.

            There are several lists of desert plants used in landscaping in the desert Southwest and Las Vegas that can be found on the Internet. Consult these lists and go to your local nursery and see if you can find some that will fit your situation.