Winter Watering Tips

Matt Sorenson

Don’t cross irrigation off the “to-do” list this winter. Your lawn, trees, and other plants still need watering to stay healthy during the colder weather.

Watering Dormant Lawns

Warm-season lawns start to turn brown and go dormant when the soil temperature drops below 55°F. In the Austin area, most lawns go dormant by mid-November.

Dormancy is a period when grass goes into hibernation to protect itself over the winter. The roots and crowns are still alive, but the blades have turned brown.

Winter irrigation helps dormant grass in a number of ways:

Prevents the roots from drying out.
Root cells full of water can better withstand cold temperatures.
Watering a day or two before a freeze raises the temperature of the soil.
Moist soil is warmer than dry soil and less likely to freeze solid.
Grass will come back greener, fuller, and stronger in the spring.

Most dormant lawns only need watering once or twice a month, and should be a supplement to any rainfall. Irrigate deeply each time to the grass root level of about 6 inches (1 inch of water).

To prevent over and underwatering, soil moisture levels can be monitored with a soil moisture sensor connected to a smart controller, or with a soil moisture meter that’s inserted into the soil. You can even use a low-tech method — push a long screwdriver into the ground. If you can insert it more than 3 inches, watering isn’t necessary.

Watering Overseeded Grass

If you’ve overseeded your Bermuda grass with ryegrass in order to have a lush, green winter lawn, you’ll have to irrigate on a regular schedule. You’ll also need to be mowing on a weekly basis.

Controllers

For winter irrigation you’ll need to make some changes to your controller programming. Modify it for just one or two waterings a month for dormant lawns.

The “seasonal adjust” feature can be used to reduce zone run times by a percentage of the time programmed for the hottest, driest time of the year. This prevents over watering during the winter.

On controllers with wifi, the seasonal adjustment is done automatically for actual conditions on the site. The automatic feature makes program changes based on: historical average weather for your area (temperature, wind speed, humidity, etc.), accuracy of the previous day’s adjustment, and the next day’s forecast. You can turn automatic seasonal adjustments on and off.

Sensors

Sensors connect to controllers, and under certain conditions pause a program to avoid wasting water. Some common sensors that help with winter irrigation include:

Rain sensors completely stop watering when they sense rain. Some accumulate a set amount of rainfall before shutting off the system, while others respond as soon as it starts to rain. When the sensor has dried sufficiently, normal irrigation can continue.

The Texas Commission on Environmental Quality (TCEQ) mandates rain or moisture shut-off devices in all new automated irrigation systems, or with any repairs calling for a controller replacement (30 TAC 344.62 (j)).

Freeze sensors turn off the irrigation system at a set temperature (e.g. 37°F). When the temperature rises beyond the set level, the sensor allows scheduled programming to run. Some freeze sensors offer a choice of cut-off temperatures (e.g. 33°F to 41°F). Freeze sensors are often combined with rain sensors, and in Texas some cities require both rain/freeze sensors on irrigation systems.

Soil moisture sensors measure the soil moisture content at the grass root level (approximately 6 inches deep), and shut down irrigation when the moisture level is adequate. There’s a choice of different moisture level set points to suspend watering. Some soil moisture sensors include a soil freeze sensor that will stop watering when the air temperature drops to near freezing.

Wind sensors prevent irrigation when the wind reaches a programmed speed. The speeds are usually adjustable, ranging from 12 to 35 mph.

Tree Watering

Most trees go dormant in the winter, and only need watering once or twice a month to supplement rainfall. Younger and newly planted trees need more regular watering until their root system is large enough to sustain them.

You’ll also need to water evergreens more frequently. Be careful not to water the foliage — it can freeze and cause damage.

Trees should be watered slowly and deeply to ensure that water soaks down to the root level. Most roots in established trees are 12 to 18 inches deep, although some anchor roots can go deeper. Use a soaker hose, bubblers, or drip irrigation to water to this depth. Also, apply water to the whole area beneath the tree canopy, and extend several feet beyond the drip line.

Usually trees need 5 to 10 gallons of water per inch of diameter. The lower amount is used for healthy trees, and the higher amount for stressed ones. You can check to see if a tree needs watering by using a long screwdriver. If it won’t insert easily into the ground 6 to 8 inches, it’s time to water.

Watering Garden Plants

Dormant perennial plants should be watered deeply a few times a month.

Winter flowering plants require more regular watering. Drip irrigation and soaker hoses are the best way to deliver water directly into their root zones. These methods avoid spraying water onto the stem and leaves, where it can freeze and harm the plants.

Balance irrigation with any rainfall. For a fail-safe way to know when to water, check the soil first with a moisture meter, soil probe, or your fingers. If the soil is dry a few inches down, then it’s time for watering.