By Tom Burfield
Growers have been raising crops in plastic high tunnels for decades, typically to have product ready to sell at the onset of the season when volume is tight and prices are high.
But those involved with tunnel production say they enjoy more advantages than just an early start.
Growers have found that commodities grown under the shelters—also called hoophouses— often have greater yields and exhibit higher quality than those raised in open fields.
That’s partly because growers are better able to regulate nutrient and pesticide applications, and they seem to end up with better water and soil quality, says Steve Boetger, state agronomist at the Natural Resource Conservation Service in Gainesville, Fla.
Boetger has seen positive effects on peppers, lettuce and tomatoes.
Good-sized high tunnels, so called because they are high enough to walk around in and to operate equipment in, can be 30 feet wide and 17 feet tall, says Teresa Salame-Donoso, horticultural research associate at the University of Florida’s Institute of Food and Agricultural Sciences Gulf Coast Research and Education Center in Wimauma.
Low tunnels typically are much smaller— about 3 feet high—and rarely used in Florida.
Salame-Donoso took part in studies in 2009 that compared the performance of three kinds of specialty melons grown in high tunnels and in open fields.
One cultivar weighed 12 percent more than those grown in an open field. And in some cases, fruit grown in the tunnels had a higher Brix level.
High tunnels offer advantages for a number of high-value crops, Salame-Donoso says.
For example, marketable volume of Florida strawberries generally starts to pick up in January, with prices often about $15 a flat. But growers who produce berries in tunnels may get a head start on the deal in December and take in $30 a flat.
“If you want to keep that market in December, high tunnels are a good thing to have,” she says.
Similarly, blueberries grown in tunnels may be ready for harvest as early as the second week of February rather than by the typical start date in April, she says.
And forget about growing colored bell peppers in open fields in Florida. You’ll likely end up with cracked or disease-ridden peppers because of rain and temperature variations.
Rain isn’t a problem in the tunnels, though, and temperatures are more consistent, Salame-Donoso says.
Alto Straughn, owner of Straughn Farms in Waldo, Fla., started experimenting with high tunnels about four years ago.
He began with 2.2 acres and will have about 40 acres of tunnels this year.
Straughn retired in 1989 after 31 years with Institute of Food and Agricultural Science, where he helped run the statewide Extension service.
He says he knew he could increase blueberry production from 50 percent to 100 percent by using tunnels and that he could move up the harvesting of his crop. But Straughn had to determine which varieties worked best.
This year, he is experimenting with smallscale strawberries, peppers and peaches as well as with high-density blueberries.
Tunnels prevent cedar waxwing birds from scarfing up his berries, Straughn can start picking early in the morning instead of waiting until the dew or rain dries and he says the berries have better blush.
Growers also can optimize the use of their land with tunnels by adding a second crop, Salame-Donoso says.
A farmer who grows strawberries from October to March can plant another crop, such as premium cantaloupe varieties or colored bell peppers, inside the structures when strawberry season is over.
And growers can save water, fuel and labor costs during a freeze if they grow in tunnels. Late in 2010, when outdoor temperatures dipped to 27 degrees, farmers were pouring water over their strawberries to prevent them from freezing—destroying the flowers and small fruit in the process, Salame-Donoso says.
Meanwhile, with the temperature inside the tunnels at a relatively toasty 43 degrees, farmers didn’t need to run water and were able to save budding fruit.
“Outside, all the strawberries were frozen,” she says. “Inside, it looks like nothing happened.” Straughn says he can reduce water use for freeze protection by up to 75 percent.
But tunnels can present some challenges, he says.
An unanticipated problem with peppers and strawberries is that the fine pine bark in which he grew them does not wet well.
Straughn solved the problem by running a lot of water on the bark, inserting old pine bark in the beds and spraying wetting agents on the bark.
He also is working to resolve some issues with pollination inside the tunnels.
Straughn used bumblebees in the past but is experimenting with honey bees as well as breaking up bumblebee quads into individual colonies and distributing them throughout the tunnels.
He’s also trying to keep the temperature down below 95 F and the humidity as low as possible. In addition, Straughn found that ventilation can be a problem.
“When it gets hot, it gets really hot under tunnels,” he says.
The price of success
The cost of the tunnels ranges from $22,000 to $31,000 per acre, plus about $2,000 for installation, Straughn says. The cost also depends on how much wind resistance you want.
Straughn uses specially made 6 mil plastic that costs $10,000 per acre but resists winds up to 65 miles per hour. You can pay less, but you’ll face severe disruption with high winds, he says.
The plastic will last three or four years, and screws, metal legs and hooks should last eight to 10 years, or longer.
You can install them yourself, Straughn says, if you have the right equipment, such as front-end loaders, a backhoe, tractors with front-end buckets and several regular tractors. Straughn rolls up the plastic in the summer, but he doesn’t take down the metal poles.
Although you can buy the components and build the tunnels yourself, that likely won’t pay off unless you have hundreds of acres, he says. Boetger of the Natural Resource Conservation Service says he expects to see greater acceptance of tunnels as growers learn how to work with them and as demand increases for organic and for locally grown produce.
For Web links to numerous resources on high tunnels, visit http://www.hightunnels.org.