By Tom Burfield
The use of water, in one form or another, remains the best method of freeze protection for Florida vegetables, experts says.
But researchers are looking at alternatives. And agencies, such as the Southwest Florida Water Management District, are offering financial incentives to growers who save water—either through conservation or by using alternative frost protection methods.
Curt Williams, assistant director of government and community affairs for the Florida Farm Bureau Federation in Gainesville, says he has looked at a number of methods of frost protection, including groundwater, frost cloth and foams.
“As of right now, groundwater is [the] cheapest, most reliable source of freeze protection,” he says. Growers of tomatoes and other vegetable tend to use seepage irrigation because it’s relatively cheap, and it keeps nutrients in the plants’ root zone, he says.
The farther south you go in Florida, the more popular seepage is because there’s more surface water, and the soil generally is less sandy than in northern Florida, Williams says.
The seepage irrigation system allows enough water to soak into the ground so that it “provides sort of a protective barrier” during a freeze event that would not be present in dry ground, he says.
Seepage systems use plenty of water, but growers can save water costs by setting up tailwater recovery systems that capture water as it flows downhill into recovery ponds.
The recovery pond captures water and nutrients so they can be reused on the plants, and it prevents nitrogen and phosphorus from leaving the farm, Williams says.
Studies under way Assistant professor Bielinski Santos, in charge of the horticulture program at the University of Florida’s Gulf Coast Research and Education Center in Wimauma, is conducting studies into freeze-protection alternatives with the help of Swiftmud.
The long-term project is looking at the effectiveness of tunnels, row covers, foam applications and reduced-water sprinkler irrigation.
“We want to develop a toolbox for growers to have different alternatives so they can pick and choose which way to go, depending on the specific situation,” he says.
Santos expects to have some preliminary results by March. Much of his work to date has been growing strawberries in high tunnels, but Santos says tomatoes also have been produced in regular soil and in soil-less cultures in tunnels “with spectacular results.”
Growers can plant tomatoes in tunnels as early as December or January instead of early February, when they’re planted in fields.
In addition to protecting fruit from the cold and saving water that would be used for freeze protection, tunnels have enabled some growers to double their yields over field production and take advantage of early-season prices.
A drawback to the tunnels, Santos says, is their high cost—$25,000 to $40,000 per acre.
Some citrus growers still use wind machines that mix arm air aloft with the cooler air at ground level, Williams says.
The machines are expensive, they cover only 10 acres or so and they offer only 3 to 4 degrees of protection, Santos says. Groundwater, however, can raise temperatures by 10 degrees or more.
Williams recently attended a meeting of the Florida Blueberry Association where he learned about the selective inverted sink— or SIS—system. It can pull cold air up from ground level and away from the fruit.
Researchers are investigating whether this method might also work with vegetables, he says.
Bill Reiss, president of BDi Machinery Sales in Macungie, Pa., who made the presentation to the blueberry growers, says the SIS system might be used to complement but not replace existing crop-protection methods for low-lying vegetables.
Some growers even use helicopters to mix up the air and warm up some high-value crops, he says.
Insulating foam has proven effective for crops, such as peppers, squash and tomatoes, but Williams points out that it’s labor intensive and can be blown away if a wind kicks up.
Frost cloth, which growers prop up with stakes and lay over low-lying plants, can provide some freeze protection, he says. .
But that, too, is expensive and labor intensive, costing hundreds of dollars per acre.
Foam cups can protect tomato and pepper transplants, says Santos, who adds that another way to reduce the chance of being done in by a freeze is to stagger your plantings.
Plant about one-third of your crop in late January, another third in mid-February and the final third two weeks later.
“If you get hit hard by the freeze, you don’t lose the whole crop,” Santos says.
Seepage works best Nothing works better than seepage irrigation for freeze protection, Randy Moss, irrigation specialist at Farm-Op Inc., the farming division of Six L’s Packing Co. Inc. in Immokalee, has found.
Saturated soil helps retain heat overnight, and sometimes that alone is enough to prevent a crop from freezing, he says. The company uses seepage irrigation during cold weather events.
Farm-Op is putting in a new tailwater recovery project and typically uses drip irrigation and microjet sprinklers to conserve water for its citrus and vegetable crops.
The company has reduced its water consumption 60 percent by using low-volume microjets and drip irrigation, Moss says.
Farm Op also has used row covers in the Naples area to protect part of its acreage of peppers and high-input crops from freezes with so-so results.
“It’s an expensive proposition,” Moss says. “Sometimes it helps and sometimes it doesn’t.”
Row covers are out
DiMare Ruskin Inc. grows staked tomatoes in the Palmetto/ Ruskin area, so row covers are not an option, says vice president Tony DiMare.
Winds also make row covers impractical.
The company has had varying success with foams—they’ve worked in some instances, but plants ended up being burned worse than without the foam in others.
Vapor Guard acts as a minimum insulator and may help raise the plants’ core temperature a few degrees, DiMare says.
The firm uses drip irrigation in Palmetto/Ruskin but runs water in the furrows to bring the water level up during cold weather.
“It creates insulation, so to speak, causing the heat to rise and warm the plant,” DiMare says.
DiMare also uses drip irrigation in Homestead, but uses overhead irrigation during a freeze.
However, the company shuts off that system if there’s a strong wind, which actually can cause more damage during a frost, DiMare says.
The cost of water is not a major concern when a grower might have $8,000 per acre production cost for tomatoes, DiMare says.
“From that standpoint, to not do anything—not ensure some sort of protection with that kind of investment—is a serous concern,” he says.