Prepared by W. Bryan Smith, Area Extension Agent, Agricultural Engineer, Clemson University and Dara Park, Assistant Professor, Water and Soil Relationships in Turfgrass Systems, Clemson University. (New 5/08.)
Winter landscape irrigation has long been considered something of 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 of this would be to heat a wet dish towel and a 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 warm the soil surface to some degree. 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 3 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 scheduling for turfgrass will be dependent on the type of grass planted. Warm season grasses grow best at temperatures 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 will require irrigation when there is not sufficient 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.
The fall and winter is when it is most important to make sure that the lawn is not on the same zone as ornamentals, trees, and shrubs. For the reasons discussed above, irrigating the turf during this time of year can be wasteful. Furthermore, if the grass is watered and then a freeze follows, the grass can be killed or severely damaged.
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.
In South Carolina, however, removing water from the piping system is generally not necessary. 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 will drain over time through the lowest sprinkler or spray head, which removes most of the water from the system. 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. And finally, the system mainline (piping between the electric valves and the water supply) will maintain water in it under pressure regardless of whether the system is winterized or not. The only exception to this 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 to be quite rare.
Adapted from the 2007 South Carolina Master Gardener Training Manual.
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