Weekly Express-News Article

By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist

Saturday, July 5, 2008

 “Watering the Lawn in a Drought”

            Over half of the water used in San Antonio in the summer is for lawn watering.  I like a green lawn just like many San Antonian’s, but most folks agree that a green lawn during a summer drought is a luxury.  It may not be necessary to forego that luxury, but it is reasonable to adopt a lawn watering strategy that recognizes the special situation in a drought and reduces water use.  There are a number of reasonable options to consider.  Here are some in order of reducing water use.

            Stage I watering restrictions in San Antonio are built around once per week irrigation by address.  Most lawns in the San Antonio area will stay green with once per week watering that provides .5 to .75 inches of irrigation.  The exceptions are those lawns or parts of lawn with less than four inches of soil.  If your home in San Antonio was built after January, 2006, and there is less than four inches of soil, the builder did not fulfill the requirements of the Water Conservation Ordinance.  Contact SAWS’ Conservation Department at (210) 704-7283 to see if there is action that can be taken.  If your house is older and you have less than four inches of soil, you will have to add soil or tolerate brown grass.

            If dry spots occur after once per week watering it indicates a problem with the irrigation coverage, or spots with compacted or shallow soil.  In the long-term, it pays to correct the deficiency, but in the short-term, just provide some supplementary water with hand-watering to address the problem areas. 

            The soil under a lawn is the water reservoir and area where the roots grow. The Hill Country and other xeriscape plants can prosper in limited soil, but a lawn needs more than four inches.  It takes a reservoir of more than four inches to provide enough water for a lawn to stay green for a week in 95° F plus temperatures.   

If you really want to provide the exact amount of water every week to keep the lawn green without wasting any, sign up for SIP (Seasonal Irrigation Program).  Go to the SAWS website at www.saws.org and then click to Conservation and to SIP.  The service is free and you do not need to be a SAWS’ customer to participate.  You provide information on your grass type and the amount of shade.  In return you receive a recommendation by e-mail each week telling you how much water is needed to keep your lawn green.  The recommendation is based on PET, Potential Evapo-Transpiration.  PET is a formula that translates weather data into water needs.  The program was developed by SAWS and Texas A&M Agrilife Extension.  It has worked for ten years. 

            Hopefully, we will not move into Stage III restrictions, but if we do, the water use reductions are based on limiting lawn watering to once every two weeks.  Lawns will not be green with irrigation every two weeks, but they will stay alive.  Watering once every two weeks is not an unreasonable strategy for lawn watering now.  It keeps the St. Augustine alive, but it also keeps your water bill low. 

            Approximately 50% of the homeowners in San Antonio do not irrigate their lawn at all.  A major advantage to this strategy is that your water bills are very low.  Lawn watering accounts for about two-thirds of the water used by families that water the lawn in the summer.  That is a lot of volume to pay for.  The other factor to consider in using water to irrigate your lawn is that the water rates increase per unit water as you use more water.  The average homeowner uses about 10,000 gallons/month.  If you use over 17,000 gallons/month you move into the 4^th tier where water costs .41/1,000 gallons, about four times the cost of water in the first tier. 

            The disadvantage of no lawn irrigation is that the lawn goes dormant.  Dormant is not the same as dead.  Dormant means brown zoysia, Bermuda, or buffalo grass that greens up as soon as it rains again.  St. Augustine grass does not have the same ability to go dormant, but it can survive a long time without water, especially in the shade and especially if you have the Floratam variety. 

            There is a variation on complete dormancy that I find desirable.  Let most of your lawn go dormant, but keep a small area around the front door and patio green by watering weekly.  This strategy avoids the disadvantage of a completely brown lawn, but can keep the water bill at a low level.