Apr 7, 2007
High Tunnels Bring High Returns

Production of fruit and vegetables in high tunnels is growing rapidly, with new growers and new crops finding their comfort zone under those plastic roofs and walls.

Producers packed the session on high tunnel production during the Mid-Atlantic Fruit and Vegetable Convention in February in Hershey, Pa. The session was organized by Penn State’s Center for Plasticulture, which has emerged as the place with the latest information on growing under plastic. Its directors are Bill Lamont and Michael Orzolek.

The movement to high tunnels started with people wanting a cheaper kind of greenhouse so they could extend the growing season, usually moving it ahead into a better price period, Lamont said. A grower in Pennsylvania, by putting up two layers of plastic film, suddenly was marketing with farmers from Georgia. One layer of plastic, one growing zone.

Although they provide some frost protection, their primary function is to elevate temperatures a few degrees each day over a period of several weeks, according to Lamont and Orzolek’s Web site, www.plasticulture.cas.psu.edu.

The system

In addition to temperature control, there are other benefits – protection from wind and rain, soil warming and control of insects, protection from diseases and predators such as birds. Organic producers are finding it easier under plastic.

“Overall, these growing systems should be considered protected growing systems that enhance earliness and higher yields, improve quality and reduce the use of pesticides in some cases,” Lamont and Orzolek said.

High tunnels encompass a crop-growing system that fits somewhere between row covers and greenhouses. They are relatively inexpensive (about $1.30 a square foot, excluding labor).

High tunnels are not conventional greenhouses. But like greenhouses, they are generally quonset-shaped, constructed of metal bows covered with one layer of 6-mil greenhouse-grade polyethylene and ventilated by manually rolling up the sides each morning and rolling them down in early evening.

There is no permanent heating, no electrical connections. The only external connection is a water supply for trickle irrigation.

“Otho Wells, an Extension specialist in New Hampshire, was a pioneer in promoting high tunnels in the northeastern United States and developed the system of production that involved covering the entire soil surface inside the tunnel with a solid sheet of 6-mil thick plastic,” Lamont said. “At Penn State we re-designed the end walls so that they can be raised up to facilitate easy access into the tunnel by a small tractor and tiller and a system of production that uses 18-inch raised plastic-mulch-covered beds with drip irrigation tape buried 2 to 3 inches beneath the bed. The raised mulch beds are 44 inches apart, which allows four rows in a 17-foot-wide high tunnel.”

The users

Among the conference speakers were Edward Weaver, who is growing cherries in tunnels; Steve Groff at Cedar Meadow Farm, near Holtwood, Pa., with tomatoes; Steve Moore at Harmony Essentials, Spring Grove, Pa., growing organic greens; and Fred Funk at Funk Farms, Millersburg, Pa., growing strawberries.

Weaver’s Orchard is near Morgantown, Pa.

“We have been growing sweet cherries for about 30 years but recently have expanded our acreage with the new dwarf rootstocks,” Ed Weaver said. ” We grow primarily tree fruits and small fruits on our 100-acre farm and sell the majority of it through our farm market and by pick-your-own.”

They have sweet cherries planted on Gisela 5 and Gisela 6.

“After numerous crop losses we began searching for a way to protect the crop and discovered the Haygrove high tunnel in spring of 2003. We constructed the first two tunnels over existing trees.”

Now, they have Hartland, Summit, Hedelfingen and Sweetheart varieties in a three-bay system (each bay 28 by 300 feet) and Ulster, Summit and Rainier in another three-bay system (two bays 28 by 450, one 20 by 450 ).

“The advantages to the high tunnels have been numerous,” he said.

They provide frost protection, rain protection and bird protection. They advance the harvest date on early cherries (Summit by one week). They reduce bacterial canker. Cherries can reach optimum maturity and can be up to 20 percent larger because they are not picked early because of rain threats.

Fruit are of higher quality, with a longer shelf life. They can be picked, rain or shine, providing a consistent supply to customers.

On the negative side of the ledger, the structures are costly, irrigation is required, and there is annual work skinning and unskinning and daily work venting due to temperature changes and storms. It’s less convenient to spray, prune and harvest compared to open fields, he said.

In addition, pollination needs more effort to get better fruit set. Early-season flowering means colder weather for bees to work in. Last year, he began using bumblebees.

Overall, “we were pleased with the 2004 crops in these tunnels, which yielded more than $10,000 worth of cherries per acre. We lost as high as 90 percent of the early sweet cherries outside the tunnels due to cracking from heavy rains.”

Weaver said the high returns are necessary because of the added cost of tunnel production, but open field production averaged $4,000 income per acre because of losses from cracking.

The nicest, tastiest sweet cherries most in demand, like Rainier, seem to be most susceptible to cracking.

“Overall, we like what we see. We’re planting another half-acre this year.”

That will bring his high tunnel cherry orchard to about two acres.

“We are also experimenting with high tunnels on raspberries, blueberries and strawberries. We have been especially pleased with the raspberries, both the lower crop loss and the increased shelf life that protection from high tunnels provides.”

Millersville, Pa., grower Fred Funk said Funk Farms has worked with strawberry production systems for many years, always striving “to get the best varieties first for our customers. Our first objective was to lengthen the season.”

Twenty years ago, they participated in the Ben Franklin Project, growing strawberries in the greenhouse during the winter using high-pressure sodium lights.

“We got to the point where we could grow nice berries, but they did not have a high enough yield to pay for the additional electric cost,” he said.

Then, he said, “I became aware European farmers were growing strawberries in tunnels. When I first heard Haygrove Tunnels wanted to visit us, I volunteered to purchase the first one to be erected in the United States.”

That first tunnel was 406 feet long by 72 feet wide by 14 feet high.

“We started the first year experimenting with tomatoes and melons along with strawberries,” Funk said. “As we expected, the strawberries showed the best potential for profit.”

They have used high tunnels for the four years since.

The research

Penn State scientists carry out an ambitious research regimen, looking for more crops to grow under plastic and to determine the best methods of growing them.

This year, Mike Orzolek described growing garlic and sweet Spanish onions in high tunnels. He found that both can be successfully produced in high tunnels. The sweet Spanish onions can be planted and harvested three to four weeks earlier compared to field production, with higher yields and bigger onions. A single 17- by 3-foot high tunnel can produce enough sweet Spanish onions for sale by a retail market, he said.

The big advantage for producing onions in tunnels is moisture control, shielding them from excessive rain that leads to rotting bulbs.

The big advantage of growing garlic in high tunnels is the ability to establish the cloves later in the year, as late as mid-November, and still produce high yields of marketable garlic cloves. The average yield of garlic grown in the high tunnels for the past three years has been 10 pounds of bulbs harvested for every 1 pound planted, he said.

Current research has also demonstrated that garlic grown in high tunnels will be harvested two to four weeks earlier compared to open field production and that higher quality bulbs are produced in the high tunnel, he said.

Penn State small fruits Extension specialist Kathleen Demchak has found special benefits in growing raspberries in high tunnels. Not only do they extend the season and allow use of better varieties, they protect the fruit from rain ¬– and the diseases that devastate raspberries.

In Pennsylvania, fall frosts result in only a small portion of the potential crop of most primocane-bearing raspberry cultivars being harvested, she said. Research was started to explore the option of extending fall raspberry production. However, it quickly became apparent that the high tunnels had more positive effects on the plants than simply extending the fall harvest season.

The fifth year of production of high tunnel brambles was just completed.

One tunnel was planted in 2000. In 2001, a second tunnel of in-ground plants was planted using a higher density, with 4 feet between rows and 1 foot between plants.

“This planting was established with organic production in mind, as it became apparent from the previous year’s planting that pesticide usage could be greatly decreased or entirely eliminated in high tunnel bramble production,” she said.

Primary pest problems were not the diseases such as gray mold that frequently plague raspberry field production. Primary pests were insects frequently seen in greenhouse production – two-spotted spider mites, Japanese beetles and whiteflies and leafhoppers.

Production of raspberries (and blackberries) was much higher than would have been possible in field production. Marketable yields of nearly 1 pound per linear foot of row (5,000 pounds per acre) were obtained with Autumn Britten the same year plants were planted, which was similar to yields that had been obtained from a three-year-old field planting at this same site, she said.

Plant growth was greatly increased, with many canes reaching 6 to 7 feet tall, rather than the more typical cane height of about 4.5 to 5 feet normally obtained at this site. Normally, primocane-bearing raspberries in Pennsylvania would only be cropped for a fall crop. However, in this system, because much potential bearing length of the cane remained to produce a second crop after the fall harvest, summer cropping in addition to fall cropping was very feasible.

Not only was the season extended later into the fall, but because the plants broke dormancy earlier in the spring, harvest began about three to four weeks earlier than normal for the fall crop.

Thornless blackberries also produced very high yield, about 3.6 pounds per linear foot of row, or more than 19,000 pounds per acre.

Quality of raspberries was very high, with percent marketable ranging from 82 percent to 98 percent, depending on row spacing, cultivar and time of year.

Early planting (at least six weeks prior to the time that planting would normally take place in the field) is needed in order to achieve good yields in the year of planting.

Organic or pesticide-free production is relatively easy to achieve, she said.

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