Heat on plants

The annual cicada mating season is close. When it arrives the air will be a cacophony of buzzing males tempting females with their sounds. It also marks the beginning of summer as no other indecator does.

They were heard in Tucson last week and central Arizona usually follows by a couple weeks.

While their presence impacts plants only comestically, their response to the summer season marks normal changes in plants adjusting for the summer. I suspect many people are not used to or ready for the changes plants are going through now.

Many trees and shrubs grown here are evergreens. Whether a pine or juniper or a braodleaf plant an evergreen nevertheless. These plants differ dramatically to deciduous plants that drop all their leaves in the fall getting ready for a cold winter.

Evergreens drop most of their leaves like their deciduous conterparts but not at the same times of year. Their leaf drop ties in with the flush of new spring growth. Some drop many leaves in preparation for the new growth. Citrus and xylosma fit this group.

Others drop most of their older leaves or needles after the new growth matures. So now we are seeing a literal shower of African sumac leaves and pine needles. This is all very common but the number of phone calls reminds me that either people forget year to year or are new to the desert.

When inspecting your plants showing leaf drop look for the following. Are the leaves/needles dropping all the same color? Are the leaves/needles dropping from other than the ends of branches? And most important, is the new growth at the end of the branches healthy?

If the answer is yes to these questions then it can be well within the parameters of normalcy.

Excessive drop I.e. more than other years has more to do with last year's care or weather oddities. One year's care shows up frequently thr nrxt year. If a tree or shrub grew at a deficit for nutrients last year the leaf/needle drop will be greater.

If this fact fits a situation give mare attention to this year's care, expecially fertilization. If the plants were fertilized in the spring and have heavy drop fertilize again lightly.

Remember most trees primarily need nitrogen. Whatever your choice for fertilizer or the suggestion from a garden center don't forget is hotter now than spring. Apply the fertilizer evenly and water it in with a large volume of water. Uneven spreading and/or a light watering may shock the plant.

If questions arise about how much or the label on the bag is confusing check with your local trained nursery professional.

Written by Terry Mikel, College of Agriculture and Life Sciences, the University of Arizona, 602-470-8086.
Material originally appeared in Arizona Republic
Return to index