Protect Your Fields From Freezes
By Robert Hochmuth and George Hochmuth
University of Florida's Institute of Food and Agricultural Sciences
Protecting crops from frost and freezes has been a continual challenge for vegetable growers in Florida. Several options are available including sprinkler irrigation, soil banking, and crop covers. Each method has application in certain areas for certain crops.
A few young vegetable crops can be protected from frost by covering with soil. This is used commonly for potatoes which have large energy reserves in the seed pierce to grow out from the soil covering. Other crops need to be physically uncovered. Early sweet corn or beans can be planted in a small trench in which the seedlings are protected from frost by the warm surrounding soil mass.
Sprinkler irrigation protects crops from freezing by providing the heat of fusion to the plant and is commonly used in strawberry production. As water freezes, it gives up the latent heat of fusion to warm the leaves. As long as water is continually applied in ample quantity, the plant will be protected. Sprinkler irrigation is less effective under windy conditions. Irrigation systems must be able to supply large quantities of water and must not be prone to breakdown. Diesel pumps should be used for this purpose since electric pumps are prone to power outages. Problems with sprinkler irrigation for frost protection include large water requirements, expensive capital outlay, possible ice and water damage to the crop, increased disease incidence, and soil erosion.
Row covers (crop covers) also can be used for frost and freeze protection. There are basically two types of row covers for commercial use: polyethylene, and porous, floating non-woven materials. Polyethylene is usually employed as a tunnel on wire hoops. Clear polyethylene provides increased temperatures by the greenhouse effect. Clear tunnels usually increase temperature too much for most days during the spring in Florida, so the tunnels need to be ventilated by perforating the plastic. White polyethylene can provide some growth enhancement while avoiding the extremely high temperatures in the tunnel.
Non-woven covers are fabric-like and can be placed over rows in tunnel fashion or can be laid on the crop in a floating fashion. Depending on the thickness of the cover, protection to 25°F is possible. Non-woven materials of 0.5 oz per yard will protect to about 30°F while materials in the 1.5 to 2.0 oz range will protect to about 25°F. Wire hoops can also be used over each row or bed to protect the crop form the physical abrasion of the row cover. Wire hoops under the cover also maximize the protection from cold damage.
Row covers for frost protection are expensive ($750-$1000 per acre) to purchase but can used for several seasons. Row covers do not have the problems associated with water as in sprinkler protection. Fruits and plants do not suffer water and ice damage and workers can enter fields readily.
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