Express-News Weekly Article
Saturday, May 27, 2006
By Calvin R. Finch, PhD,
SAWS Water Resources Director, and Horticulturist 
“What Makes Lawn Water Efficient?”   

            It may surprise you to know that zoysia grass, characterized as a water efficient grass, takes as much water to stay green as St. Augustine grass in the summer.  Zoysia grass is drought tolerant, not because it does not require much water to stay green; it is drought tolerant because it can go dormant when water is short without permanent damage.

 

            As the zoysia grass example illustrates, the question of water efficiency is not a simple one.  It addition to differences between species of grass, and even selections of the same species; the soil quality and depth; the amount of sun on the lawn; and even irrigation patterns determine how efficient any lawn is.

 

            Based on tests conducted over four years on 64 lawns in San Antonio, a St. Augustine lawn in full sun with at least four inches of soil will require about .75 inches of water per week to stay in good condition.  In the shade that same St. Augustine grass only requires about .5 inch per week.  Zoysia grass requires about the same amount of water as St. Augustine to stay green in sun or shade.  Bermuda grass and buffalo grass only prosper in the sun.  The Bermuda grass will require on average only .5 inch to stay green and the buffalo grass even less, about .38 inch per week (3/8’s of an inch).

 

            As was mentioned earlier in the article, zoysia grass will go dormant if there is not enough water to meet its needs.  Bermuda and buffalo grass have the same capability.  This dormancy is expressed by a brown color.  When the rains begin again, the grass greens up within a few days.

 

            St. Augustine does not have as much ability to go dormant because of drought.  Brown color in St. Augustine grass is an expression of cold dormancy or dead grass.  Most turf experts describe that St. Augustine grass requires more regular watering than the other South Texas Lawn grasses.  In the same tests that determined St. Augustine’s need for .75 inches of water per week on average to stay green, it was determined that .5 inch every two weeks was required to keep the lawn alive.

 

            Of all the St. Augustine grasses, tests in Waco and other turf demonstration plots reveal that Floratam St. Augustine is consistently the most drought tolerant of St. Augustine selections.  In the demonstrations, it often stayed green longer than all other grasses.

 

            Soil depth and quality is a factor in the amount of water a lawn needs to survive and stay green.  The demonstration determined that six inches of soil is significantly better than less than four inches of soil.  If that soil is enriched with compost, it is particularly efficient.  Even St. Augustine grass grown in the shade on six inches of good compost enriched soil can survive without supplemental irrigation in a typical San Antonio summer.  The deep soil provides a large reservoir for water storage.  The compost addition means that air can penetrate the whole soil profile and the roots can functionthroughout the reservoir.

 

            When you buy a new home and want a lawn, insist on four inches of soil enriched with compost to make up at least 25% of the total soil.  Maintain the quality of your soil under an established lawn with top dressing and aeration every year.

 

            Lawns with four inches of soil do well when they are watered once per week.  Add the required irrigation at a rate that allows it to penetrate all the way into the soil reservoir.  Avoid runoff by adding the water in brief allocations.  Three applications of ten minutes each over the course of three or four hours can be very efficient and will probably apply the required 75 inches of water for a typical St. Augustine lawn in full sun in the summer.  If you really want to be efficient in your irrigation, participate in the SIP (Seasonal Irrigation  Program).  It is a personalized lawn watering program based on your lawn type, amount of sun, and the weather data each week.  Individuals who enroll receive a SIP kit complete with instructions and the equipment you need to determine how much water your irrigation system is putting on your lawn.  For more information on efficient lawn watering and to enroll in SIP, visit www.saws.org and click to Conservation and then SIP.