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October 3

Efficient turfgrass irrigation depends on you

Q. I want to plant a lawn with a grass that uses less water than ryegrass. Do you have any suggestions?

B.L.
Raton

A. Dr. Bernd Leinauer, NMSU Extension Turfgrass Specialist provided the following answer to the question about grass varieties.

I am frequently asked about plant selection but this question cannot be answered without addressing two other areas: human expectations and irrigation system performance. I hope my answer will help clear up some general misconceptions about water use by turf.

A plant's water requirement is a very important aspect of plant selection here in the arid Southwest. During the summer outdoor watering accounts for 50% or more of urban domestic water use. Turfgrasses, which can make up for a large portion of our landscape are consequently identifid as "water guzzlers." Therefore, conventional wisdom would suggest that removing our traditional grasses (such as Kentucky bluegrass, perennial ryegrass, or tall fescue) and replacing them with grasses that are considered "low water use" (buffalograss, blue grama, bermudagrass) would conserve large amounts of potable water. However, other factors need to be considered also.

The climate in New Mexico can be very challenging when it comes to plant selection. Our summers are dry and hot, but winters are cold and can also be dry. Generally, it is easier in our climate to maintain cold tolerant plants in the summer than drought tolerant, cold sensitive plants in the winter. Therefore, cold tolerance is usually the first characteristic considered when selecting perennial plants, whether they are turfgrasses or shrubs and trees. In addition to cold tolerance, many of our turfgrass areas have to survive and recover from all sorts of abuse, including sports such as baseball, football and soccer, and regular traffic from children and pets. It is therefore no surprise that Kentucky bluegrass, perennial ryegrass, and tall fescue are considered desirable grasses for our lawns, as they are the only ones that combine traffic aesthetically pleasing for many of us during most of the year. This brings us to our next question: which cold and traffic tolerant grasses use less water?

When selecting plants for water conservation, it is important to decide what your quality and functional expectations are. Do you want a green, playable surface that withstands traffic almost all year round or simply a landscape with ground cover where color or lack thereof is not important? If traffic tolerance is not a consideration, we can use other cold tolerant grasses with a lower irrigation requirement than Kentucky bluegrass and the other aforementioned cool season grasses. Buffalograss and blue grama are native grasses with cold tolerances that make them suitable throughout New Mexico. These grasses will withstand mowing heights of greater than 4 inches or can be left unmowed as ornamental grasses. Unfortunately they can only be used in areas that receive little or no traffic, where the main purpose is to contribute to the aesthetics of a landscape. Furthermore, buffalograss and blue grama are warm season grasses that go dormant (lose green color) during mid to late fall and stay colorless (grayish to tan colored) until late spring or early summer. Lawn areas planted with buffalo or blue grama require little or no irrigation during dormancy. Buffalo lawns look different from a traditional Kentucky bluegrass or fescue turf, as the plants' canopy is more open and less dense and uniform. It has more of a "meadow" appearance than that of a traditional lawn.

You may have noticed that I avoid the term 'water use' but instead use the term 'irrigation requirement.' It has been our observation, particularly in residential areas, that turfgrass areas are being irrigated well above what is required because of a lack of knowledge of how much water is needed. The blame is put on the grasses which are labeled "high water users" when in reality these grasses would do just fine with less water. The question we should ask is not how much water do turfgrasses use, but with how little water can they survive and meet our quality expectations. All turfgrasses, including Kentucky bluegrasses and tall fescue can survive with less irrigation water using mechanisms that allow plants to adapt to drought. Furthermore turfgrasses can survive longer periods even in the summer without any irrigation. Grasses simply go dormant and lose color (just like in the winter) but will turn green again after the water has been turned on. We have buffalograss test plots at NMSU in Las Cruces that have not been irrigated for 2 years, but green up for a brief period of time after every significant rain fall. The plots show green color only for a total of 4 to 6 weeks per year. This may not be acceptable for those of us who enjoy the green appearance throughout the summer, but it shows how resilient some of the grasses are. Even Kentucky bluegrass will use the dormancy mechanism and lose color in the summer when exposed to drought but will recover when rain or irrigation resumes.

If sprinklers are used to irrigate, an audit with catch cans will tell us how much water is applied and also how uniformly it is spread. A Colorado survey of over 6,800 irrigation audits conducted throughout the Southwest showed that the average residential irrigation system has a distribution uniformity of 50% regardless of which sprinkler head was used. In order to irrigate all areas of a lawn adequately with an irrigation system that has a 50% uniformity, the amount of irrigation water doubles compared to what "the grass plant needs" to maintain an adequate quality level. This suggests that a poorly functioning irrigation system may contribute more to water wasted in turf irrigation than the grass species selected.

In summary, before you implement a drastic change to your landscape by either completely removing the turf or changing to a different kind of grass consider the following: 1) Ask yourself what your quality expectations are. 2) If your irrigation is applied by a sprinkler system, conduct an irrigation audit and learn how much water is applied with every irrigation cycle. 3) If you feel that you are wasting water by irrigating your lawn, start watering less. You will reach a point when the turf quality declines somewhat, but this slight decline in appearance may be acceptable and may result in significant water savings. 4) Consider alternative irrigation systems (such as subsurface drip) that apply water more uniformly and more efficiently than traditional sprinkler systems. 5) Use warm season grasses such as zoysiagrass, bermudagrass, buffalograss, and blue grama if you determine that a change in species will not affect the purpose and functionality of your lawn.

Your County Extension Service can help organize specific irrigation workshops that will cover topics from proper plant selection, to conducting irrigation audits and using the Internet to schedule irrigation, if there is interest and sufficient participation. The Southwest Turfgrass Association holds its annual conference in Ruidoso during the second week of October. Speakers from NMSU and other universities present on topics and latest research findings on the sustainability of urban landscapes in the Southwest. Check it out at www.southwestturfgrass.com or contact your Extension Office for more detailed information.


For more gardening information, visit the NMSU Extension publications World Wide Web site at http://aces.nmsu.edu/pubs/_h.

Send your gardening questions to:

Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd. SW
Los Lunas, NM 87031

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.