Storm Trees

The primary concer about the summer storms has to be the potential damage to property and plants. But what about the rain?

The rains of last weekend came in different amounts in different parts of the area. Some places received less than and some places received more than an inch total for the weekend. That seems like a lot of water and should alow a significant reduction in the irrigation of plants.

For the vegetable, lawns and flower beds the rains were enough to save a couple waterings. The same for small shrubs. Trees and large shrubs barely felt benefit.

To understand why it did not significantly help the large plants lets look at what rain water as a source.

Water applied into the usually heavier textured soils of the Salt River Valley does not penetrate that deeply. For the heavy silt- or clay-loam soils one inch of water moves in about 6 to 8 inches. The potential of getting one inch of rain and haveing it all stay on you property and go into the soil wetted less than a foot deep.

It does wet the rootzone of smaller plants. It is not enough to wet the rootzone of larger plants.

Rain storms and the water it brings does clean the air, wash the dinge off leaves, gives us a temporary break from the sun and heat and supply some nitrogen for plants. This is good. Rains also trigger a reaction in plants to literally open up their pores to get more water. This actually increases the plants' demand for water.

If the storm causes this reaction but does not give enough water to supply the extra demand some plants actually can wilt.

Additionally, the rain water is much purer than the water we put on. The water normally used has a certain level of salts that accumulate in the soil. When the very pure rain water comes it can dissolve much of the excess salt and put it into a saltier solution than before. This can release more salts and begin to seal up the surface of the soil.

This phenomenon can be seen by the little puddles that form and standing water lasts much longer than if the depression were filled with regular water.

It seems nonsensical to water during or just after a rain storm. Experienced gardeners know that while the storms are exciting and bring some relief to the humidity and temerature depending on the rains for effective plant watering for large shrubs and trees just doesn't help.

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