The writing on the wall is crystal clear. Texas’s population is growing, and new sources of water are either rare or very expensive. The days of just “turning on the sprinkler” are becoming the days of weather-related irrigation based on research, weather data and modern technologies.
Turf may not use more water than any other landscape plants. That honor goes to large plants such as shade trees. But turf tends to be the most irrigated plant in our landscapes. Considering the large expanses of turfgrass in most landscapes, this means that much of our summer watering ends up on the lawn. In fact, about 60% of average home water use is for outdoor irrigation.
It is a general truth that most lawns are overwatered in much of the state. When I lived in the Houston area, which receives around 50 inches of rainfall per year, it wasn’t unusual to see my neighbors watering three times per week.
You may often hear the general rule that “turfgrass needs about an inch of water (via rainfall or irrigation) per week to stay healthy.” While that is generally true, the rule is more accurately applied to the summer months. In winter, irrigating is very seldom advised. In spring and fall, the milder conditions may drop that requirement by half. But even this more nuanced recommendation doesn’t account for weather conditions and the demands these conditions place on turfgrass.
Watering Based on Local Weather
Turf researchers have studied the question, “How much water does turfgrass need?” Turf-water use depends on several factors, including turf-soil conditions, but is primarily influenced by sunlight intensity, wind speed, humidity and temperature.
Mini-weather stations are now set up across the state to measure these factors so that a computer can determine the evapotranspiration (ET) day by day and week by week. Evapotranspiration (ET) is a measurement of the total amount of water removed by evaporation from the soil surface and also by transpiration as grass releases water in evaporative cooling. We perspire, plants transpire. The term ET comes from evaporation (evaporation of water from the soil) and transpiration (loss of water by plants through their leaves).
Turf research has determined what percentage of ET is required for turfgrass to either thrive or to survive with an acceptable level of health and quality. The data can be overwhelming to homeowners, but a growing number of programs has made it quite simple.
The website https://watermyyard.org serves numerous cities in Central and Southeast Texas as well as the region around the Houston metroplex. Check to see if they cover your city. If not, ask your city water department to join the network.
This network of weather-data collecting stations will allow you to sign up for a weekly email notifying you about how much water your lawn has used in the previous week and how much water your lawn needs.
For those not living in the Water My Yard area, contact your local water provider to see if they offer a similar service. It not, go to https://texaset.tamu.edu where you can find a local weather station to know how much you need to water. While weekly emails are not an option in this system, it allows you to find the closest weather station and to see the water use data from the past 3, 5, 7 or 14 days.
Weekly Watering Schedule
The long-term goal is to water once, or at most twice, per week by applying one inch of water per week. This is for sunny areas. Shady areas can be watered much less frequently.
I should point out that water loss from the soil is related also to soil type, compaction, grass-plant health and depth of the root system. For example, two lawns side by side may not perform equally with the recommended “deep and infrequent soaking” or one inch applied once per week.
If one of these two lawns has a loamy soil with healthy deep-rooted turf and the other has a dense, compacted clay with turf struggling with disease issues, then the latter will need a little less irrigation, but more frequently, until the compaction and plant-health issues are resolved.
Irrigation-Technology Advances
Irrigation technology has improved in recent years, such that we have options when it comes to irrigation-system application heads.
The old pop-up, spray heads put out water at a rate of 1.25 to 1.5 inches per hour, which is usually faster than the soil can absorb it. Rotor heads send out a stream that rotates from left to right and back across the lawn. Rotors apply water at a .75 to .83 inch per hour rate and are more efficient than spray heads.
Multi-stream rotors irrigate at a rate of .3 to .5 inches per hour by applying water in a series of smaller streams that drift across the irrigated area like a rotor does, except rather than traveling back and forth across the area, the streams appear on one side and disappear as they reach the other side of the area being watered. The multi-stream rotors are very efficient and can significantly reduce or eliminate runoff losses.
In addition to better application heads, we have many types of “intelligent” controllers that can be set to various water-saving settings. Some even have the ability to connect to local weather-station data and apply the needed amount based on when your lawn is likely to need supplemental watering. An older technology that is unfortunately underutilized is the rain switch. These block the irrigation cycling for a few days after a rain, and then allow the cycle to resume. This prevents watering during or soon after a rainstorm.
Cycle and Soak
It is often the case that you cannot apply an inch of irrigation at one time without runoff. Clay soils absorb water very slowly, and sloped areas are prone to runoff. If your irrigation system puts out water at a rate faster than the soil can absorb it, runoff can be avoided by using a cycle-and-soak technique.
This means watering until you reach the point of runoff. Then turn off the water and allow about 45 minutes for the water to soak in well. Then follow this with another application of water and repeat as needed until about an inch of water is applied.
For a quick and easy way to know how long your system should run to apply an inch, set some rain gauges or simply some straight-sided cans (from canned vegetables, cat food, tuna fish, etc.) around the area and run the sprinklers for about 20 minutes. Measure how much water is in the rain gauges or cans and multiply times 3 (20 minutes × 3 = 1 hour). This would tell you how long it takes for your irrigation system to apply an inch of water.
What Time of Day?
The best time of day to water your lawn is early in the morning. I aim for around 6 or 7 a.m., but this time period is not a rule for everyone. The goal is to avoid watering in the heat of the day, when evaporative losses are the greatest or in the evening when the grass would tend to stay wet for hours, which can increase some disease issues.
Evaluate Your System
Irrigation systems are often poorly designed or installed. I’ve discussed options for efficient system timers, improved application heads and rain switches. Perhaps the simplest thing you can do is to observe your system when it is running.
Do the spray heads apply water such that water from one head reaches to the next head? This helps increase uniformity of application. Are the heads vertically oriented or leaning significantly? Are they aligned to only irrigate the lawn, not streets and driveways?
Is the pressure sufficient to reach all areas with an application of coarse droplets of water? Excessive pressure results in mist that usually drifts to other areas. Are any heads broken or missing? Are all heads of the same type? Combining spray heads with rotors or multi-stream rotors will not provide an even application of water across the lawn. So, you end up overwatering some areas to make sure other areas don’t become drought-stressed.
You can spread out a group of rain gauges or straight-sided cans to evaluate your systems’ uniformity of application. Better yet, in many areas there are irrigation professionals who can come to your place and do an official “irrigation audit” that includes the things I mentioned above, and much more.
Technology has provided us many opportunities to irrigate more efficiently, both to avoid wasting water and to promote healthy turfgrass. As the population of our state grows, with minimal new sources of water, conservation is more important than ever. tg
By Robert ”Skip” Richter
Brazos County Horticulturist
Texas A&M AgriLife Extension Service