The most important thing you can do for your landscape during the summer months is also the simplest: WATER, WATER, WATER.
Chicago summers are hot, and plants need you to make sure they have moisture. This not only keeps them growing, but also helps ward off diseases that attack plants weakened by thirst.
Don’t over-water, though. Plant roots need oxygen, and too much continuous water keeps the soil from breathing. Water thoroughly and then allow the soil to dry enough so that the air can penetrate before watering again.
When you water, water well. Just wetting the leaves and soil surface quickly may do more harm than good. This encourages plants to develop shallow roots that will be extremely vulnerable in dry spells or to sudden freezes.
Most people don’t have the time or patience to water a whole garden with a handheld hose. Use a sprinkler. Until you become accustomed to the rate your sprinkler distributes water, you may want to use a rain gauge (or a cup or can) to measure. A measured inch of rain or sprinkler water will penetrate the soil about 10 inches. In dry periods, water at least a measured inch every week. Note that it may take several hours for a sprinkler to distribute an inch of water.
Interestingly, a 35-foot tall tree loses 30 gallons of water on a hot summer day. During a dry spell, even large trees must be watered to ensure good health and promote growth. Give special care to all new plants. Trees, shrubs, evergreens and groundcover planted within the past four years should be considered newly planted. Generally, soaker hoses deliver insufficient water for newly planted trees and shrubs. When you water, water well.
The simplest rule of thumb? If your plants are looking dry, water them!
