Plants are 75 to 95 percent water. A large shade tree can transpire-- lose water through it leaves -- up to 100 gallons of water a day.
Water is essential to a great many plant processes. Lack of water, especially when coupled with great heat, slows down these processes. This is often called heat dormancy, although the lack of moisture is at least as responsible for it as the heat. The plant compensates for the stress by relative inactivity, and ordinary cultural practices, instead of being beneficial, can induce further stress. Fertilizers will burn dry root hairs, pruning can force the plant to use reserves to make new growth, and pesticides may be toxic to dry foliage.
Drought Defined In The Home Landscape
There are a number of technical definitions for the condition called “drought”. In the home landscape the broad definition would be any period of time without any rain that is sufficient in length to cause plants to become stressed. Generally you can assume the plants in your yard are experiencing stress if they have not received any water for two weeks. This situation is usually called a “dry spell”. Drought occurs over an extended period when rainfall is seriously below normal for your area. Generally, your local weather service will announce when they determine a drought is in process in your area.
The long and short of it is when plants don’t get sufficient water over a long period of time they will experience serious stress, and in many cases the plant will die prematurely. A tree that experiences a serious drought may not die for four or five years, but the cause will often be primarily the experience of that drought five years before.
While a drought will certainly affect any plant on your property, usually the trees and shrubs get overlooked when the yardener waters the lawn and flower beds. So be aware that your trees and shrubs are just as vulnerable to drought as is the lawn.