Cool season lawn grasses go dormant during hot dry summer weather. During the dormant period the grass is brown and will not recover from injury or compete with weeds. Once a dormant lawn is adequately watered, it greens up and begins growing again.
It is necessary to water lawns that will be kept green throughout the summer. It is not necessary to water to keep the lawn alive. Whether or not to water is a decision that must be made before the lawn goes dormant. Starting a watering program, especially if the lawn is fertilized, and then stopping, can be more harmful than allowing the lawn to go dormant at the beginning of the dry weather. Do not start watering if the watering can not be kept up through the entire dry period.
Early morning watering is preferred. This provides water during the heat of the day and little water evaporates due to high temperatures.
Watering may be done during the heat of the day but more of it will evaporate due to high temperatures. Wind may affect water distribution during mid-day waterings.
Lawns require 1- to 1 1/2 inches of water per week. This is about 640 gallons per 1000 square feet. A garden hose would normally take about 2 hours to apply an inch of water to 1000 square feet. Sandy soils will require two watering per week to maintain adequate moisture levels.
Apply the water before the lawn actually goes dormant and when it begins to wilt. Wilted lawn grasses will have a bluish cast and footprints will persist for some time. Once wilting occurs, begin watering.
How the water is applied is important. Sprinklers should apply the water evenly over the entire area. To determine how long it takes a sprinkler to apply an inch of water, put cans at different spots in the sprinkler pattern. Turn on the water and keep track of the time it takes the sprinkler to put an inch of water in all the cans.
Apply the water only as fast as the soil can absorb it. Heavy clay soils absorb water slowly. After the surface layer is wet, the water may run off rather than soak into the soil.
Any rainfall must be considered as part of the inch of water for the week. Summer rain often comes in the form of thunderstorms during which a lot of water falls in a very short time. Since much of this water runs off, it is not captured by the soil for plants to use. Do not consider short, intense rainstorms as providing a significant amount of water for lawn growth.
Homeowners with underground sprinkler systems should set the system to apply water for 20 minutes each day at noon.
Lawns infected with certain diseases have circles of dead grass with green grass in the middle. These symptoms can be reduced by watering lightly every day to reduce moisture stress.