Winter Irrigation
Winter landscape irrigation has long been considered an oxymoron in the Southeast. A good portion of South Carolina’s 48 to 52 inches of annual rainfall finds its way to Earth during this time. Plant growth is slowed considerably (if the plant is not dormant), and temperatures are cool. Plant water needs during this time should be adequately provided by rainfall.
There is a time in the winter when lawn irrigation in the South may be beneficial. First, we have to understand that water will hold heat energy. A simple example would be to heat a wet and dry dish towel to the same temperature. Place both towels on a counter and check them for warmth 30 minutes later. The wet dish towel will be warmer simply because the water in the dish towel retains heat more readily than the “air” in the dry dish towel.
Similarly, wet soil will retain heat more readily than dry soil. During a winter day, the sun can somewhat warm the soil surface. If the soil is wet, this heat is lost slowly during the evening and night hours. Lawn grasses subject to cold damage may be less likely to suffer cold injury due to the longer heat retention of the moist soil.
It is not necessary to irrigate weekly during the winter. However, if there has been an extended dry period (say three weeks or more), adding 1 inch of water to the landscape during a warm winter day may help prevent cold injury to the lawn.
Winter Irrigation & Grass Type
Winter irrigation scheduling for turfgrass will be dependent on the type of grass planted. Warm-season grasses grow best at temperatures of 90 to 95 °F. Cool-season grasses thrive when temperatures are 65 to 75 °F. Warm-season grasses commonly cease to grow and may turn off-color in South Carolina during winter. In comparison, cool-season grasses will actively grow and maintain their color until the coldest of our winter months. Because they are growing, cool-season grasses require irrigation with insufficient rainfall. Although many lawns in South Carolina are warm-season turfgrass species, during fall and winter, these lawns may be overseeded with cool-season grasses for aesthetic reasons. For overseeded conditions, apply irrigation when rainfall is not sufficient.
It is most important to ensure that the lawn is not in the same zone as ornamentals, trees, and shrubs in the fall and winter. For the above reasons, irrigating the turf during this time of year can be wasteful. Furthermore, if the grass is watered and a freeze immediately follows, the grass can be severely damaged.
Winterizing the System
Many landscape companies offer to “winterize” irrigation systems. This usually involves draining water from pumps (if a surface water body is the water supply) and pumping compressed air into the system to force any water out of the piping.
Removing water from any surface-water pumps is a must for the winter. Even a tiny amount of water left in a pump casing can freeze and crack the casing, requiring some expensive repair. As little as ¼ inch of water in the bottom of a pump casing has been known to freeze and crack a pump casing.
However, removing water from the piping system in South Carolina is generally unnecessary. First, the piping is usually placed 12 inches below the ground surface. At that depth, the water in the piping will not freeze in our climate. Second, most systems drain over time through the lowest sprinkler or spray head, removing most of the water. This does mean that the lowest head on any section or zone may have water in it over the winter and may freeze, but it is generally not a problem. Finally, the system mainline (piping between the electric valves and the water supply) will maintain water under pressure regardless of whether the system is winterized. The only exception is if the system has a surface water pump.
Drip tubing is extremely flexible, so even if drip systems are placed on top of the ground, freezing is not an issue for them. There has been an instance of a low-lying emitter freezing over winter due to runoff collecting in the depression, but that seems quite rare.
Summary
- The need for winter irrigation is dependent on the type of turfgrass grown.
- Warm-season grasses do not require winter irrigation but may benefit from an occasional addition of water during extended dry periods simply by helping retain heat in the soil.
- Cool-season grasses may need occasional irrigation during extended winter dry periods, but will not require nearly as much water as during the spring and summer months.
- Ensure turf is not on the same irrigation sections or zones with ornamentals and showy annual beds, where winter irrigation may be required to maintain blooming.
- Winterizing an irrigation system is generally not required in South Carolina (except for above-ground pump drainage). However, there are no detrimental impacts if you do choose to have it winterized.
- Above-ground pumps should always be drained completely unless they are housed in a heated location.
Adapted from the 2007 South Carolina Master Gardener Training Manual.
Document update 4/24 bu Rob Last and Bryan Smith.
Originally published 05/08
