May 15, 2014

University of Arkansas, Division of Agriculture
Turfgrass Science Program (http://turf.uark.edu) – Turf Tips

Whoa! It’s too early to be irrigating your lawn.

With the arrival of warmer weather this month I’ve noticed some home owners have fired up their irrigation system to water the lawn. Although it was fairly hot last week, it's not yet time to be irrigating home lawn turf. Most lawns in Northwest Arkansas will not need supplemental irrigation for several weeks as our soils have plenty of moisture to maintain turf growth throughout the spring. This is due to the combination of winter ice and snow melt, spring rains, and relatively cool temperatures that evaporate moisture from the soil at a much lower rate compared to summer months. I advise homeowners to refrain from irrigating their lawns until visible wilting is present, which typically occurs around late June on my lawn in Fayetteville. So, what’s the harm in irrigating your lawn now? After all, you’ve invested in a nice irrigation system and you enjoy watching it run. Well, here are a few drawbacks of over-irrigating your lawn:

1.) Less Healthy Turf. Lawns that are irrigated frequently will remain relatively wet near the surface. This results in a shallow rooted turf that will be less drought tolerant later in the summer. In contrast, as non-irrigated soils dry in the spring, turfgrass roots extend deeper into the soil to access the moisture there, which results in a much better developed root system. A lawn with deeper roots will not only be more drought tolerant, but will also have better recuperative potential in case of injury due to insects, disease, or traffic.

2.) Expensive Water Bills. Although I consider Fayetteville city water a bargain at $0.0052 per gallon, irrigation costs do add up when you consider how much water it actually takes to effectively irrigate a home lawn. When irrigation is necessary, we generally recommend applying 1 inch of water per week in two to three applications. It takes 27,000 gallons of water to apply an inch of water to an acre, so a medium sized, quarter-acre lawn would require 6,750 gallons weekly to irrigate, ultimately adding $140 to your monthly water bill.

3.) Public Perception. I’m particularly sensitive to this final negative consequence of over-watering the lawn. Home lawns are often the target of public criticism as being “water wasters” when, in reality, turfgrass species are among the most drought tolerant plants used in the landscape. It’s noteworthy that turfgrasses originated in arid, droughty regions of the world and are therefore naturally drought tolerant relative to other plant species. Anyone who has traveled west on I-40 or I-70 has probably noticed how the natural landscape changes from trees to grasses in western OK and KS as there is not enough annual rainfall there to support tree growth and yet grasses persist. Nevertheless, we see articles such as the opinion piece that ran in this past Sunday’s (5/10/14) New York Times, which referred to turfgrass lawns as a “toxic brew” that require “constant watering”. Of course that is simply not true, especially in humid climates like ours where we average 40 inches of annual rainfall. In fact, turfgrass lawns can survive year after year in Arkansas with no supplemental irrigation- they may just go a little brown during hot and dry summer periods, but will bounce back quickly following the next rain shower. Unfortunately, the myth that lawns require constant watering is perpetuated by too many home lawn irrigation systems that are running either early in the growing season, or every day, or during / following rainfall events.

So, what is the best way to utilize your automatic irrigation system?  First, turn the main dial to “off” so that your programs do not continue to run unnecessarily (Photo 1).  Next, set up a program that will apply enough water to wet the soil to a 3 to 4 inch depth (his typically takes 0.5 to 0.75 inches of water, which will require run times of 30 to 60 minutes per zone for most residential systems).  Then, set the program start times daily for the early morning hours to ensure that the program will run every morning that the main dial is switched “on”.    Finally, wait until you see some visible drought symptoms in your lawn (remember, a little drought stress will ensure a deep root system) and then turn on your program so that it runs the next morning… and don’t forget to return the dial to the “off” position when the program has finished.  The above strategy takes advantage of your automatic irrigation system’s capabilities while eliminating the possibility of over-watering and all of the related negative consequences discussed previously.  One exception to delaying lawn irrigation for now is if you are establishing turf from seed, sprigs, or sods, which all lack an extensive root system and cannot access moisture deeper in soil (Photo 2).

For those of you that want to take some extra steps in conserving water while maintaining your lawn, here are some additional considerations:

• Use improved irrigation controller technology. Many newer irrigation controllers can utilize rainfall or soil moisture sensors, or even weather data to adjust programs so that water is only applied when needed.

• Use a drought tolerant cultivar. Recent research has identified turfgrass varieties that exhibit superior drought tolerant characteristics. More information is available at www.tgwca.org.

• Grow deep roots. In addition to allowing the soil surface to dry, deep turfgrass roots can be produced with good mowing and fertility practices as well as core-aerifying areas where the soil has become compacted.

I’m a bit tired of hearing about lawns wasting water, so let’s make sure we’re all doing our part to irrigate only when necessary and not flame the fires of this myth.

Doug Karcher and Mike Richardson
Department of Horticulture
University of Arkansas


Photo 1. Leave your irrigation controller in the "off" position until the lawn begins to wilt. Then set the controller to irrigate the following morning.


Photo 2. This sod was recently laid on campus and was not irrigated. It did not survive because it lacked a root system to access water deeper in the soil.


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