Just a few short weeks ago we were wondering when the rains were going to stop. Currently in central Iowa, many lawns are dormant because of lack of rain. Homeowners have two options for lawn care when it comes to hot, dry weather. One is to simply allow the turf to go dormant. The other alternative is to properly water the lawn to maintain green turf throughout the dry spell.
Kentucky bluegrass (which is the most widely planted turfgrass) can survive extended periods of drought by going dormant. Dormancy is a natural survival mechanism for cool season turfgrasses. The foliage ceases growth, wilts, and turns brown as the turfgrass plant enters dormancy. While the foliage is dead, the crowns and roots remain alive. The maximum length of this dormant period varies from lawn to lawn and is largely dependent upon the condition of the turf. Most healthy lawns can survive in a dormant state for 4 to 6 weeks without rainfall or irrigation. However, lawns that have been damaged by insects or have excessive amounts of thatch my be killed by several weeks of hot, dry weather. Lawns that are growing in poor soils are also susceptible to drought damage. If your soil is poor, has excessive thatch, or is damaged by insects, water regularly to prevent the lawn from going dormant. Healthy lawns that have been allowed to go dormant should recover when the turf receives sufficient water. However, recovery is often slow. It may take 2 to 8 weeks for the grass to fully green up.
After 4 to 6 weeks of dry conditions, dormant turf should be watered to prevent possible drought damage. Apply 1/2 to 3/4 inches of water in one thorough irrigation. This amount of water will not cause the turf to green up but will provide moisture to help the crown and root system survive. If the dry weather persists, water dormant turf with 1/2 to 3/4 inches of water every two weeks. Following the onset of favorable moisture conditions, either through rainfall or irrigation, the turf will develop new leaves and begin to grow actively.
Those persons desiring green turf throughout the summer should begin to water the lawn when symptoms of moisture stress begin to develop, but before the grass becomes dormant. A good indication of water stress in turfgrass is leaf color. The normally green leaves become a dull blue-green. Additionally, water-stressed turfgrass is less resilient. Footprints remain in the turf after walking across it.
Turfgrass requires approximately 1 to 1 1/2 inches of water per week, though actual amounts vary because of soil type and weather conditions. Turf should not be watered by a set schedule. Scheduled watering can lead to overwatering which wastes water and creates favorable conditions for some weeds and diseases. Automatic irrigation systems should be set to start for a single irrigation cycle only and then shut off until the turf requires water again.
Water turf deeply to moisten the soil to a depth of 6 to 8 inches. Deep watering promotes the development of a deep, extensive root system which can withstand stressful weather conditions better than shallow rooted plants. Slopes or areas with soil compaction are often a challenge to water. Do not apply water faster than it can be absorbed. On slopes and compacted soils, irrigate for a short period of time until the water just begins to run off and then stop. Allow the water to penetrate and infiltrate into the soil and then water the area again until runoff begins. Repeat this cycle several times until the soil is wet to a depth of 6 inches.
Before beginning an irrigation program, homeowners should consider the amount of time, labor, and water required to maintain a lush green lawn. Once you begin to water a lawn, it should be continued throughout the dry period. It is more stressful for the turf to begin a watering program and then stop because the water bill was too expensive than it would have been to have gone dormant naturally. Applying 1 to 1 1/2 inches of water each week to a large lawn will require a large amount of time (unless you have an automatic sprinkler system) and water. An application of 1 inch of water to 1,000 square feet of lawn requires 640 gallons of water.
Sprinklers are the best way to irrigate turf. Irrigation equipment varies from a sprinkler head attached to a hose to an underground sprinkler system. Hand watering is impractical and not recommended.
Water turf early in the morning (4 to 8 a.m.). Winds are generally light and temperatures cool so very little water is lost through evaporation. Watering at midday is not harmful (as many people think), but it is less efficient because evaporation is often high and strong winds may cause uneven water distribution.
As the dry weather continues, consider existing soil and lawn conditions, cost and labor involved, and your expectations when deciding whether or not to irrigate the turf this summer.
This article originally appeared in the July 19, 1996 issue, pp. 128-129.