Super greenhouse


By George DeVault
Originally posted in August 2002

Farmer Steve Moore used to grow 22,500 kg of early tomatoes in 900 square meters of heated greenhouses each spring.

“It was a good money-maker,” Moore says. “It really filled in in the early spring when we needed some cash flow for us and our wholesaler. The wholesaler supplied 14 markets in and around Washington, D.C.”

But Moore says he felt he was also creating a monster.

“We were four years into tomato production and realized that we were burning 1,500 pounds of propane in 10 days to heat this greenhouse, pumping fuel oil from a 2,000-gallon fuel oil tank and buying oil on futures to lock in prices with our distributor.

“Wow! we said. This is a strange detour for a family that has been farming with horses and trying to live a sustainable lifestyle for 27 years,” Moore recalls.

“We need to make some changes. We have to save our own energy, too. We have to have less work, use less unsustainable energy and we need better nutrition, fresh food instead of all of the canning we were doing. We went back to square one.”

Moore abandoned his big, fuel-guzzling greenhouses and began experimenting with simple, homemade structures that burn no fossil fuel whatsoever. He bought plastic pipe, cut up big sheets of old greenhouse plastic, scrounged used plastic water pipe and put them all together in simple structures that harnessed the power of the sun.

Steve with his daughter.

“The materials cost us $200 per house. We recouped that the first cutting of lettuce,” Moore says.

Gradually, experimenting with different greenhouse designs and materials, Moore finally worked his way up to his present greenhouse, a 8.5- by 29-meter structure that helps to feed 130 families every week from mid-March almost to mid-December.

“It really looks like a standard greenhouse. It is embarrassingly simple,” he admits. “Ventilation consists of louvers and wide double doors at each end that are opened by hand. The key is to have a lot of airflow in a greenhouse to reduce disease and other problems. Growing in healthy soil, we don’t have to worry about disease as much.”

Proper planning captures the sun’s heat
There are no mechanical devices in the greenhouse, other than a small blower used to inflate the two layers of 6 mil plastic that cover the greenhouse. The blower produces insulation by creating a create a dead air space between the layers of plastic. Perhaps more importantly, it also keeps plastic taught so that it is not affected much by wind. There are no fans for heating or cooling.

Being solar-heated, the greenhouse capitalizes on solar gain, stores it in the earth and also is supplemented by the ambient heat of the earth, which is 55 degrees F (about 13 degrees C).

“The bigger the greenhouse the less perimeter area there is to the volume. Because of that you have less heat loss from the surrounding area. The less heat we can give away and the more we can store is a better deal.”

Proper planning is critical from the beginning. “Light is the key element to growing in the winter. Even deciduous trees will shade a greenhouse in the winter. You can give up hardly any light at all. Make sure that you know your site and understand the limitations of the sun on the horizon throughout the whole year. It’s really important,” he says.

The Gothic arch design gives better penetration of sunlight and ventilation than the usual half-round Quonset hut style greenhouse. It is oriented east-west instead of the usual north-south so that you get the maximum amount of solar gain with the largest amount of surface facing south, Moore explains. “The arch design is much stronger than Quonset-style greenhouses and also sheds snow and ice more readily.”

Of course, you can’t grow tomatoes in a greenhouse like this during the off-season, the grower says. But Moore can — and does — grow many other things out of season. For example, he plants some potatoes inside the greenhouse the day after Christmas and harvests them in March.

“We are in production from the third week in March and the week before Christmas when the farmer gets worn out. We could really run year-round if the farmer didn’t get so worn out, and I think we will have to find a way to do that.”

Moore worries about losing customers during his present mid-winter lull in production. “Whenever you leave and don’t serve that market somebody will fill that void. If you can keep products going every week through the year it makes a huge difference.”

Grow tunnels inside the greenhouse capture still more heat

Moore is always on to new and better ways to hold more heat inside. Old greenhouse plastic is cut into long strips and draped over five permanent beds inside the greenhouse to create what Moore calls grow tunnels. Heat-holding brick walkways underlain with foam insulation separate the beds. The plastic is supported by bows of old plastic water pipe. The bows are anchored on short sections of steel reinforcing rod driven into the ground on either side of the beds.

“The grow tunnels appreciate some more heat,” Moore says. “We pull the plastic back during the day. The sun warms earth, then we pull plastic back on at night.”

Moore uses plastic sheeting on the outside of the greenhouse for four or five years until its ability to transmit light diminishes. Then he replaces the outer coverings and uses the old plastic for up to six more years in the grow tunnels.

In March, growth inside the greenhouse is so vibrant that the inner covers are no longer needed. Moore moves the bows and plastic on to outside beds where they are erected on metal posts lining the beds. In midsummer, many bows are covered with shade cloth, which allows Moore to produce sweet, juicy lettuce through summer. Moore grows more than 10,000 heads of lettuce for his CSA customers.

The ends of the greenhouse are framed with lumber. One end is covered with bi-walled, 8 mm polycarbonate panels. The other is draped with plastic sheeting that is held on with old drip irrigation tape and staples.

When the temperature outside dipped to -27 C last year, the thermometer read -8 C inside the greenhouse and grow tunnels. That’s cold, but not cold enough to permanently damage Moore’s lettuce and other cold-hardy greens.

Yields are impressive. Last year, 12 square meters of Oriental Express eggplant produced 608 fruit weighing 78 kg. That is 6.8 times the average U.S. yield. Nine square meters of Ace green peppers yielded more than 10 times the U.S. average, producing 923 peppers weighing more than 75 kg. Forty Sun Gold hybrid cherry tomato plants produced 2,500 to 4,000 juicy, sweet tomatoes each week.

“It gets really hot in our greenhouse in the summer with only natural ventilation, as you can imagine. These are tropical crops and they just love the heat,” Moore says.

For pollination, Moore relies on honeybees and bumblebees from hives that he keeps nearby outside. He grows some yarrow and buckwheat inside the greenhouse to help attract beneficial insects.

“We don’t spray anything in our greenhouse, not even organically approved sprays,” he adds.

“We’re feeding 130 households, plus 20 percent of our production by design goes to the Salvation Army for the food bank in Chambersburg.”

Moore has managed to produce abundantly with far less expenditure of money and unrenewable resources. “We think small and try to leave more of the natural world alone as we scale our farms down to do a much better job with what we have.”

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