It is no mystery why row covers are replacing overhead irrigation for spring frost protection of strawberries.

There are several reasons. Barclay Poling, recently retired North Carolina State University Extension horticulture specialist, says, one of the most convincing he ever heard came from a grower near Raleigh, N.C.

“His words were ‘I want to sleep!’” says Poling.

This grower had relied on overhead sprinkler irrigation for spring frost protection until he started experimenting with row covers in the late-1990s, he says. The all-night watering sessions required for frost protection with overhead irrigation were eliminated with row covers. 

Now, the only reason he has to use a sprinkler system might be for evaporative cooling and an occasional late-season windborne freeze during bloom, says Poling.  

“A floating row cover of 1.5 ounce-per-square-yard weight can do the same job as overhead sprinkler irrigation for frost protection,” he says.

You can also save a lot of money on the fuel bill for pumping water,” he adds. And by keeping the crop “dry” with covers, it isn’t necessary to spray nearly as often for botrytis during the bloom period.

The distinct disadvantage of overhead irrigation for frost protection is that it uses such a significant volume of water. It also causes erosion in the row middles and ends, and it washes pesticides from the strawberry and leaches fertilizers from the field. 

By comparison, strawberry row covers conserve water, reduce soil erosion, and reduce fertilizer leaching. They can also reduce spraying relative to conventional overhead sprinkler irrigation.

There are important limitations to using row covers for certain types of cold protection, especially when temperatures are expected in the low twenties or the teens during bloom.

Sprinkler irrigation has been the accepted practice for frost protection for many decades, says Poling. “If a grower did not have an adequate water supply for overhead sprinkler irrigation system, he or she was advised not to go into strawberry production.”  

The water requirement for an overhead sprinkler irrigation system is usually estimated on the basis of three consecutive frost or freeze nights, he says. For example, 5.4 acre-inches of water would be needed for sprinkling at the rate of 0.18 inch per hour for control down to 24 degrees F., for 10 continuous hours each night over three nights.  Or 1.8 inch per night for three nights equals 5.4 acre-inches. 

“An irrigation pond would need to hold about 150,000 gallons of water for each acre of plasticulture production under these conditions,” says Poling. “That’s a lot of water.”