Like most of you, I struggled through those blistering hot days of July and August with plants wilting in the sun, leaves and blooms of roses crinkly and scorched. Despite watering twice a day, it wasn’t enough. So, what could I have done? Well the old layers of mulch come to mind, but I’d already done that, and heaving heavy bags of bark in the blazing sun, adding more was NOT an option.
Since roses are mostly water, giving additional water was partly the answer. Heat stress is a major cause of wilting, burned and yellowing leaves. This type stress is usually most noticeable when we have a sudden shift from cooler spring weather to very HOT weather. The rose bush has to acclimate to this sudden shift and thus transpires out more moisture than it takes in. The need to water more, up to five to seven gallons per bush is necessary. Also helpful is to spray the roses with a nice bath VERY early in the morning.
The use of anti-transpirants can be helpful. These chemical aides form a thin coating of a waxy substance that retards evaporation but does not impede the stomata from allowing atmospheric gases to enter the surface cells. There are several types of anti-transpirants; while these agents are sprayed on, preferably in early morning on a still day (no wind), caution must also be used that the temperatures will not exceed 90 degrees, as some burning of the leaves can occur. (Catch 22 isn’t it?)
Now that we have a slight break in our extraordinary temperature readings, time to get out and do the plant protection before we hit the huge digits again.
By Barbara Lanoy Picarelli, Master Rosarian Emeritus
Edited for the website by Nanette Londeree, December 2019