Farming Magazine – January, 2011

GROWING

The Backwards Greenhouse

Opposite growing conditions for winter tomatoes

By Kathleen Hatt

“What you normally see with greenhouses, we do just the opposite. We use lots of lights and heat, but comparatively little ventilation,” says Dan Nelson who, with his wife Terry, grows winter tomatoes hydroponically in their Wentworth, N.H., greenhouse.

From July planting to November harvest

By starting seeds in mid-July, the Nelsons can have their hydroponically grown Hobbit Hill Farm tomatoes ready for market in November when fresh, locally-grown tomatoes are no longer available. They begin by seeding Trust, a popular variety of greenhouse-grown beefsteak tomato, into Oasis Horticubes. After seeding, the rigid, open-celled, water-absorbing foam cubes are placed under grow lights in a barn room. When seedlings are about 4 inches tall, they are transplanted into plastic net pots filled with coconut fiber. The tender seedlings are grown in net pots until they are large enough to tolerate the heat of a greenhouse designed for cold weather use. In late August to early September, 8-inch plants are put two to a 5-gallon black plastic bag filled with wet coconut fiber. The blocks of coconut fiber are soaked in a children’s plastic pool prior to planting.

Once in black plastic bags, the plants are fed a solution of nitrogen, phosphoric acid, potash, magnesium and sulfur plus trace minerals. The solution is pumped automatically through pipes in the greenhouse. The exact composition and strength of the solution and the number of times per day plants are fed varies with the amount of natural and artificial light they receive and their stage of development. Fans help keep the young plants from scorching in the late summer sun. To prevent the rapidly growing plants from tipping over, they are fastened with small plastic rings to 20-foot lines attached to a pulley system. As the plants grow upward, the lines are lowered. By the end of the growing season, a single plant may have 20 horizontal feet of growth.

When plants are about 12 inches tall, soon after they have been put into the greenhouse, the first flowers appear. Like field-grown indeterminate tomatoes, the plants flower at different rates and produce tomatoes throughout the growing season. To encourage development of perfectly shaped tomatoes, the Nelsons limit flowers to three per cluster. They also pick off suckers every few days. Using what he calls his Harry Potter Wand (a battery-operated vibrating stick), Nelson goes through the greenhouse every other day gently shaking pollen from flowers. The entire operation takes approximately 20 minutes. By November, the first red, vine-ripened tomatoes are ready for picking. Like tomatoes vine-ripened in summer, Hobbit Hill Farm’s hydroponic tomatoes ripen from the inside out.

Keeping tomatoes healthy and growing

“It’s a game,” says Nelson of the play of nutrients, heat and humidity in the greenhouse. To ensure

it’s a game they have a fair chance of winning, the Nelsons send leaf samples to Waters Agricultural Laboratories in Kentucky for analysis. The test they generally have done monthly shows how well the plants are absorbing nutrients. Early on, the Nelsons learned that the $15 test is money well-spent. “Sometimes it’s smart money to make better money,” says Nelson.

For solutions to problems with anything in their greenhouse but the structure itself, the Nelsons turn to the source of all their Bag System hydroponic growing supplies, Hydro-Gardens of Colorado Springs, Colo. “They’ll spend hours on the phone with us if we have a problem—no charge!” says Nelson.

Because Hobbit Hill Farm greenhouse is operated primarily in winter, plant diseases, especially airborne ones, are minimal. A ground cover, white to reflect LED lights, black elsewhere, also deters insects. Aphids, however, can be an issue, and when they are, ladybugs are used to control them. The Nelsons use no pesticides. Nematodes, a million of them once a month, control fungus gnats. Mixed with water and sprayed in the black plastic growing bags, the nematodes eat the fungus gnat larvae.

The winter greenhouse

The 30-foot-by-60-foot greenhouse in which the Nelsons grow their winter tomatoes is covered with two layers of polyurethane. Warm air is pumped between the layers, and a fan operates every few minutes to circulate warmed air throughout the structure. Rigid pink polyfoam sunk into the ground helps insulate the bottom 2 feet of the building.

An outdoor wood furnace heats the greenhouse to 78 degrees during the day and 64 degrees at night. Keeping a plastic structure warm from September 1 through May 30 in northern New Hampshire where temperatures occasionally dip to minus 30 degrees takes wood, and lots of it—generally 24 to 25 cords a season. The Central Boiler, Classic model, is usually fed twice daily, at 7 a.m. and 10 p.m. When temperatures drop to between 20 and minus 20 degrees, however, filling may increase to three or four times a day. Cutting and stacking wood is Nelson’s summer job. He cuts $100-a-cord log lengths into 2-foot lengths and stacks them in a hoop house where they remain dry throughout the winter. The furnace can accommodate logs up to 3 feet, but the Nelsons find logs that big difficult to handle.

The light switch

When Dan and Terry Nelson began growing winter tomatoes three years ago, everyone said it couldn’t be done—well, it could, but it came at a price. Tomatoes need light, and they can utilize up to 20 hours of it a day. The high-pressure sodium (yellow) lights originally installed in the greenhouse consumed electricity at a rate that often resulted in a monthly bill of $1,000. Because the high-pressure sodium lights consumed so much power, they also challenged the greenhouse wiring and could not be run as long or as efficiently as the Nelsons—and the tomatoes—would have preferred. To reduce the power draw in the greenhouse, the sodium lights had to be run in sections, resulting in each plant getting only about 15 hours of light a day.

In October 2009, the Nelsons installed LED lights in their greenhouse. Not only have the three-wavelength LEDs halved the cost of electricity, but, because they draw much less power, they have also made it possible to run more lights in the greenhouse more often. The greenhouse formerly had 20 high-pressure sodium lights. Now, it has 24 electronically controlled LED lights, which can all be run at the same time. Nelson estimates that the LEDs themselves are 70 percent more electrically efficient than the high-pressure sodium lights.

Some question the use of LEDs for growing, says Nelson. Do LEDs produce the same growth rate as high-pressure sodium lights, or is the rate better or worse? For the Nelsons, receiving half their former electricity bill is answer enough.

Help with the switch

At the time that Nelson was researching the feasibility of replacing the farm’s high-pressure sodium lights with expensive state-of-the-art LED tri-band grow lights, he learned of two grants, both designed to reduce carbon footprint. For the commercial energy efficiency grant offered by New Hampshire Electric Cooperative (NHEC), the Nelsons’ electric utility company, Nelson filled out a two-page application. “They were fantastic to work with,” says Nelson. The request was approved the day after it was submitted. Within one week following installation of the LED lights from High Tech Garden Supply in Cranberry Township, Pa., NHEC personnel came to inspect the project. The following week, they handed the Nelsons a check.

The USDA application was a bit more complex. A binder filled with application forms in quadruplicate, an electrical audit, three supplier bids, permits (which in tiny Wentworth, N.H., meant a letter from selectman explaining the lack of permits due to the absence of zoning), six months of frustration, and the Nelsons’ continued commitment to the project, eventually resulted in a grant. Together, the NHEC and USDA grants covered 53 percent of the nearly $24,000 cost to install LED lights in Hobbit Hill Farm’s greenhouse.

To market, to market

Dan delivers the tomatoes grown at Hobbit Hill Farm to 12 restaurants and markets within about 25 miles and 40 minutes of Wentworth. The 20-pound cases of tomatoes are custom-picked for each customer. For a year-round produce market and for a small grocery store, tomatoes are picked to maximize shelf life. For restaurants, the Nelsons pick a mix to provide ripe, but not over or under ripe, tomatoes for several days.

Experience to share

Four years of experimenting with various small greenhouse systems and three years of growing Bag System hydroponic tomatoes have yielded many perfect tomatoes, a few not-so-perfects and many experiences Dan and Terry Nelson are willing to share. The two lifelong gardeners say that what they have learned growing tomatoes first as a hobby and now commercially is information easily transfers to other crops, such as peppers and greens—which could be grown organically, but at added cost. “There’s no glut in the winter tomato market, we have no plans to expand, and the price of LED lights will be coming down,” says Dan. “We welcome visitors. If we can help you not make the mistakes we did, great!”

There’s one thing the Nelsons did not expect when they set out to grow tomatoes in winter. “It’s been fun!” they say in unison. “We’re making people happy, and they’re always happy to see us coming.”

Kathleen Hatt is a freelance writer and a frequent contributor to Farming. She resides in Henniker, N.H. Comment or question? Visit and join in the discussions.