High tunnels can extend season and improve yields, quality

07/11/2013 03:37:00 PM
Tom Burfield

high tunnel covering strawberriesCourtesy University of FloridaHigh tunnels, also called hoop houses, can extend the season and protect crops from weather.High tunnels, also known as hoop houses, have exploded on the scene growing from a few acres the past decade to more than 1,500 acres.

The Quonset-hut-like structures are sometimes referred to as “poorman’s greenhouses” and consist of a frame—typically metal poles—over which plastic sheets have been stretched.

Blueberries, strawberries and peaches are some of the crops grown in high tunnels, and some growers have expanded into tomatoes, peppers, miniature peppers, okra, cauliflower and melons.

Squash that, in the past, had to be imported during December through February now can be produced in tunnels, enabling growers to get top dollar, says Dan Cantliffe, county Extension director for the University of Florida’s Institute of Food and Agricultural Sciences in St. Johns County.

Raison d’etre

High tunnels serve many purposes.

They protect crops from cold weather and can eliminate the need to run overhead sprinklers during freezes, saving money, product and water, Cantliffe says.

Tunnels prevent “rain check” or water marks on tomatoes that can occur during rainy weather and interfere with ripening.

High tunnels also help growers control the timing of their crops and help ensure consistency, says Bob Hochmuth, multi county Extension agent for the Suwannee Valley Agricultural Center in Live Oak.

In addition, they allow growers to produce a high-quality crop at a time when they otherwise could not. This can help growers gain a better market position, primarily by starting their harvests earlier, he says.

Today, there is “broad statewide distribution of usage and technology that was minuscule three years ago,” Cantliffe says, largely because high-tunnel technology has improved and their costs have dropped.

Developers now are looking at heavier gauge plastic that resists weather, diffuses light, reduces ultraviolet light and heat, and even has qualities that stop fog that forms under the plastic from dripping onto plants, he says.

Offsetting costs

Production costs increase when you grow in tunnels, Cantliffe says, but the higher yields and returns from improved marketing timing can offset the initial costs.

Many growers reduce pesticide use and use biological controls instead, saving money on chemical inputs.

Tunnels typically range from about 50 cents to $2 per square foot—or about $20,000 to $80,000 per acre—and are about 30 feet by 180 feet, Cantliffe says. He recommends that they be 14 to 16 feet high to allow room for hot air to disperse.

The structures typically can be depreciated over 10 years, but they have at least a 20-year lifespan, he says.

Although high tunnels can be found statewide, most of the large concentrations are in Central and South Florida, Hochmuth says.

They present a unique advantage in Florida because many consumers in urban centers now want locally grown, high-quality specialty crops.

Even small-scale growers often can meet that demand because they can achieve greater yields on less acreage, he says.

Grower experience

William “Skeeter” Bethea, a crop specialist for Enza Zaden specializing in tomatoes and peppers for the East Coast, logged 25 years as a conventional grower before venturing into developing high tunnels and the seed varieties best suited for them.

Bethea, who’s based in Myakka City, is conducting a commercial demonstration trial in a series of connected high tunnels with passive ventilation designed to “get the heat out.”

Inside the tunnels are several tomato varieties along with peppers and cucumbers.

“You can’t build any business on inconsistent product flow,” he says. And an overheated tunnel can disrupt that flow.

His tunnel design, which has been picked up by Tunnel Tech of Tilsonburg of Ontario, Canada, features end-cap vents and roll-up doors to aid airflow.

Yields from 1 acre of a high tunnel can equal those from 7 acres of open-field production, Bethea says.

Challenges

The biggest challenges in setting up a high tunnel are the upfront invest ment—the cost of the structure—and making sure the structure can withstand the environment, Hochmuth says.

In Florida, that often means high winds.

High tunnels create a very different environment than what growers are used to, he says, so you’re going to have to change some growing practices.

For example, pest pressure is different.

Instead of the common pests that you might find in the field, the dry greenhouse environment may result in more pests, such as spider mites and powdery mildew.

You also may have to change your variety or cultivar choices.

“[Growers] have to be in a position to make a wise choice in terms of what cultivar they’re going to grow,” Hochmuth says. “That’s where we are having a hard time keeping up with the demand for information.”

If you have a large operation and the equipment to do soil fumigation, you can continue to use it or switch to a soilless environment, Hochmuth says.

If you’re a smaller operation just getting into tunnels and don’t already have fumigation equipment, you’ll probably want to adopt a soilless culture, such as coconut fiber bags or containers filled with composted pine bark.

Location also is important to ensure proper airf low, Cantliffe says.

“If you’re in a situation that doesn’t have airflow, you’ve got a problem,” he says.

So don’t set up your high tunnel in an area surrounded by buildings or in a valley that could get cold or wet.

When setting up a high tunnel, Bethea advises growers to “adapt to fit your environment.”

A common mistake growers make is building a tunnel too long. He suggests a maximum of 300 feet.

Bethea also recommends a north-south orientation. An east-west orientation under Florida‘s winter sun can bake crops on the south side and slow maturity on the north side.

“Ventilation strategy is important,” he says.

If you just put a plastic roof over your tunnel, “you get convective heat buildup, like an oven,” Bethea says.

He actually builds an “attic” in his tunnels to shield plants from the heat.

The higher the better, he says. Bethea’s tunnels are up to 14 feet high.

He also includes rain gutters, up to 80 inches long.

Altogether, Bethea estimates his tunnels cost about $30,000 to $100,000 per acre.

“It’s worth the investment to be able to handle the adversities and be consistent,” he says.



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