Spring Growth

Summer 2003

Adam Montri of Michigan State University and two Maine growers spoke about hoophouses at MOFGA’s 2011 Spring Growth Conference. Videos of the talks are posted at www.youtube.com/watch?v=CMf_Og8xWXE, www.youtube.com/watch?v=RIpsP3SvyQI&feature=relmfu and www.youtube.com/watch?v=ItQL0ca3IfU&feature=relmfu; more information is available at www.hoophouse.msu.edu.

Adam Montri
Adam Montri of Michigan State University spoke about hoophouses at MOFGA’s Spring Growth Conference. English photo.

Montri, associated with the MSU student farm, helps small and midsized farms increase production and economic viability. He and his wife also have their own small farm.

Sighting and Sizing

Regarding siting, consider where subsequent houses may be, said Montri. If houses run east and west, the one on the north should be as far from one on the south as twice the height of the southern one – so a 10-foot-tall house should be 20 feet from the next house to prevent shading. At the student farm, an experimental plot of strawberries is growing between houses.

Width, Length, Height

Houses may be 20, 26, 30, 34 or 35 feet wide. Montri prefers the greatest width, because “you always have about 2 feet of marginal growing space on the edge where it’s wettest, coldest, darkest all through the winter.” In a 20-foot-wide house, 2 feet on each side means 20 percent of the growing space is inferior; a 34-foot-wide house has less marginal production space.

Hoophouse bows are usually spaced 4 feet apart. Wider spacing requires bigger ground posts and trusses to support snow loads. So lengths tend to be 24, 48, 72, 96, 144, up to 200 feet – “but that’s a big sheet of plastic to put on,” said Montri. A 20- by 96-house is similar in area to a 30- by 48. With the 30 by 48, “you get the width early on. When you’re ready to expand, you can remove the end wall, buy more bows and buy a 100-foot sheet of plastic instead of 50-foot.

Spending about $500 extra for taller ground posts increases the clearance, so the 2-foot edges with marginal growing conditions become places for walkways, and the middle, warmest part of the house becomes growing space.


Above 40 degrees north latitude, run houses east-to-west for year-round production, said Montri, to gain more light and thus more heat. But often, outbuildings or the shape of the property dictates that a house go north-south, “and it works.” For summer production only or for season extension for warm season crops, light is sufficient, so houses can run either way.

Light, Temperature, Humidity

In unheated houses, October is about the last time growers can plant, and around February 1 to 15, light starts to become available again.

Plant health can suffer with day and night winter temperatures swings. If the temperature reaches 55 in the tunnel in winter, condensation and disease occur, so venting the house at about 50 F in winter is important.

A ridge vent moves a lot of air but costs about $3,500, so is probably not worthwhile for vegetable production (but is more important in floriculture), said Montri. Zimmerman and Harnois have more affordable models with simpler ridge vents that can be opened with a hand crank or automated.

End vents that are 51 inches square and automatically open at 50 degrees via a thermostat help a lot but require electricity. A hoophouse far from a source of electricity can use butterfly end vents, which pivot on a piece of conduit screwed to the outside frame of the end wall. The grower must be present to open and close them.

Growers usually open butterfly vents first, then a door, then roll-up sides – partway or all the way, just on the south side or on the north and south, not when it’s windy, etc., for multistage cooling.

Because roll-up sides take a beating, Montri is trying a woven fabric that is 10 or 12 mils thick and is supposed to last eight years. His own house also has a thermostatically controlled motor to roll up sides. The system cost about $1,800 from Advancing Alternatives (www.advancingalternatives.com). The thermostat can be set for the temperature at which the motor runs, how long it runs, and how long before another temperature is read. Montri’s is set to take a reading, open the sides partway, wait 10 seconds, take a reading, and roll sides up more if necessary.

Alternatively, sides can drop down from a hip board so that cold air doesn’t rush onto plants. Montri doesn’t see production differences with these, but he thinks roll down sides can keep wind from damaging plants. Water can collect in the rolled down sides and support algal growth, so growers might crank the sides up after a rain to remove standing water.

Large doors, such as a garage door, or removable end walls can increase ventilation – although one grower who did this had deer walk into his house.

Bed Layout

Montri runs beds widthwise rather than lengthwise. So a house could have 2-foot walkways on the sides, 3-foot beds centered on side posts, and 1-foot walkways between beds. Tracking crops can be easier in shorter beds; more importantly, air flows better past tall crops such as tomatoes, and light hits both sides of plants, helping reduce diseases. Also, beds centered on bows have a built-in truss, as trusses go from bow to bow.

Montri suggested that a 3-foot walkway on the south side of a house and a 1-foot on the north would give more room for a wheelbarrow on the 3-foot side.

A single-harvest crop, such as carrots kept over winter, could conceivably be grown in a house with no walkways by harvesting from one end to the other.

The width and arrangement of beds in a 30- by 96-foot (2,880-square-foot) house affects the percent of bed space available:

23 beds at 3 x 26 feet = 1,794 square feet = 62 percent bed space use
7 beds at 3 x 90 feet = 1,890 square feet = 66 percent
5 beds at 4 x 90 feet = 1,800 square feet = 63 percent


Overhead spinners have different, adjustable nozzles to vary pressure and spread. These aren’t used much in Michigan because dissolved bicarbonate in the water clogs small holes; and high-iron well water stains plastic orange, dramatically decreasing light.

One option to dragging hoses is to have overhead headers with hanging hoses, so growers can water two beds in each direction comfortably.

Most growers use two lines of drip per bed, especially on transplanted crops. For direct seeded crops, such as salad mix, or carrots at 2-1/2-inch spacing and 12 rows per bed, drip would displace two rows per bed, decreasing production. “So for direct seeding, we’re watering mostly by hand,” said Montri. “Also with drip, by the time the end rows are wet, the middle is too wet.”

Growers water once every three to four weeks in winter, depending on how sunny it is and how wet the ground was going into the winter. “A lot of it is spot watering.” Montri has 7-foot frost-free hydrants with 4 feet below ground.

Internal coverings

Internal coverings trap heat closer to plants. Poly is more durable and holds more heat than row cover but must be opened quickly on sunny days.

The student farm houses use one big cover about 40 inches high; Montri believes this holds more heat than covering individual beds. The height prevents the cover from touching crops, so condensation won’t settle on them, and they won’t freeze from touching the cover on cold nights. Also, growers can get under the cover to harvest. This system cost about $250 to $300.

Since Montri and his wife aren’t home in the daytime, they have four runs of high tensile wire running the length of their hoophouse, supporting three sheets of 40- by 30-foot row cover rather than plastic. This system cost about $65 to set up.

Farmer Panel

Tom Roberts and Lois Labbe of Snakeroot Farm in Pittsfield have three metal bow houses and one that they built from cedar and spruce poles. Its wooden framing creates 6- by 6-foot sections where they can use good pieces of plastic that they remove from other houses. They use old drip tape as batten to hold the plastic to the wood.

They remove all old plants from the house in the fall and till compost into the beds – the only fertility provided each year.

In late November or early December, they plant spinach or spicy greens, lettuce, carrots and beet greens in unheated houses. Between late December and late January, seedlings are up. “We want just the first seed leaf produced by then,” said Roberts. “If we push things too fast, they grow so fast that crops are ready before markets are ready.”

Their one heated house grows beet greens, turnip and carrots.

In summer they use a weed whacker to cut hay for mulch in greenhouses.

They start seedlings for their 5 acres of gardens and to sell at the farmers’ market. They made low cedar and spruce tables that are as wide as an aisle and hold trays of seedlings between every other bed in the house in spring. At the same time, cool season crops grow in beds. They harvest small patches of these and transplant warm season crops, such as tomatoes and cucumbers, in the patches while the rest of the cool season crops continue to grow.

Roberts thinks low Quickhoops will work as well for them as hoophouses, since he wants to extend the season but not grow in winter.

Mark Guzzi and Marcia Ferry grow 10 acres of mixed vegetables at Peacemeal Farm in Dixmont and sell primarily at farmers’ markets. The like their 26- by 96-foot “Ed Person greenhouses” from Ledgewood Farm in New Hampshire (www.ledgewoodfarm.com). Their hoophouses are used primarily to produce salad greens and spinach from the first day of farmers’ market to the end, “which used to be the beginning of May to the end of October,” said Guzzi. “Now there’s this new phenomenon of the endless farmers’ market, where the people expect you to go all winter long. One of our main markets goes twice a month all winter, outdoors.” They now have spinach until the second Saturday of January and start selling it again on the second Saturday of March.

“The easiest thing to do is to overwinter spinach,” said Guzzi. “You can plant it almost as late as you want. As long as it comes up, it will survive the winter, and when the light comes back in spring, it will take off. The flavor is incredible.”

They start heating part of one house the first week of March to germinate 350 flats of onions in a “giant germination chamber” – one greenhouse bench stacked upon another with a tarp over the top. Heat directed under the benches stays within the tarp area. Other beds in the unheated part of the house grow spinach.

Their tomatoes and peppers in hoophouses produce earlier, later and better crops, and tomatoes have less late blight.

“We can ripen orange peppers in the hoophouse but not in the field,” said Guzzi. “Throw them in with the red peppers, and people think you’re awesome.” Habanera peppers wouldn’t grow in the field but do great in a hoophouse.

Diseases are appearing because Peacemeal repeatedly raises tomatoes and peppers in greenhouses. One possible rotation crop is zucchini, which produces and sells well a couple of weeks before field zucchini. Pole beans are convenient to trellis to overhead cross ties, are very productive, and taste much better than bush beans.

Crop Rotation in Greenhouses

Organic certification standards require that vegetable crops be rotated; growing tomatoes every year in one house fails that requirement.

Roberts rotates cucumbers, tomatoes, cherry tomatoes and peppers. He also puts a basil plant between each pepper plant. “It’s crowded, but peppers don’t seem to mind being crowded,” he said.

Guzzi plans to remove the old plastic on one house and grow a crop outside all summer. In the heated greenhouse, he raises seedlings on alternate sides each year. He thinks that watering them three times daily leaches salts from the hoophouse soil.

Montri suggested rotating tomatoes, cucumbers, sweet potatoes and cut flowers – if you have a market for flowers.

When rotating crops after chickens, Eric Sideman said the crops can’t be harvested for 90 or 120 days, according to waiting periods required by organic standards after manure applications.

Dave Colson grows greens for half the year, then tomatoes, basil and peppers for the other half.

Nicolas Lindholm said he’d like to rotate more than two families, longer than four years, and add cover crops. Colson said that adding good compost builds as much or more organic matter than crop rotation. Sideman recalled a Vermont grower who rotates soil: He removes 6 to 12 inches of soil every two or three years and brings in a new, composted soil mix.


Regarding rodents, Sideman said voles will feed on fall planted spinach. He mentioned Eliot Coleman’s vole trap (shown at www.mofga.org/Default.aspx?tabid=844).

Regarding sanitation, one grower removes everything – plant tissue, nests, etc. – in early December and adds compost while the ground is soft. By the following March, “it’s been a desert in there from December to March. Except for some disease spores that overwinter in the soil, it’s a good way to get rid of some insects or diseases.”

Roberts lets an occasional unobtrusive weed remain and uses the edges of houses to grow garlic over winter, planting in fall to produce scapes in May and cloves in June.

Lisa Turner said that when she grew greens all winter, aphids became a problem – including on seedlings she started in the front of one house. “Now I let that house freeze all winter and start seedlings there in spring.” She said Eliot Coleman starts watering in January even if plants don’t need it. “I tried that this year and it worked like a charm. I think it reduces the nitrate buildup in the plants,” which can otherwise attract aphids.

Sideman noted that sanitation won’t control such ubiquitous diseases as gray mold, leaf mold and verticillium, but others might be reduced by cleaning. Oxidate (a hydrogen peroxide solution) is labeled for organic use but kills beneficial organisms, too.

Temporary Structures

Caterpillar tunnels are simple temporary structures, built in hours by driving rebar into the ground in two rows, 4 feet apart along each row, and bending 20-foot pieces of PVC piping from one piece of rebar to another. Plastic is stretched over the pipes, and rope is pulled over the plastic and tied to posts between those supporting the piping. These structures, usually built in April and taken down in September, don’t withstand wind or snow. Guzzi said, “A temporary structure is probably great, until it blows away. And then you’ll wish you had purchased the permanent one.” One grower said plants can’t be trellised in PVC tunnels but can be in tunnels made with metal conduit and purlins. He had one that survived a snowy winter.

A representative from Johnny’s Selected Seeds said that low Quickhoops can be made 4 or 6 feet wide from PVC, which doesn’t hold snow so well, or from metal electrical conduit. The hoops are first covered with row cover, then, before snowfall, with 10-foot-wide 4 mil plastic secured by sand bags along edges.

Top Money Crops

Asked to list their top money crops, Roberts answered, “Almost anything no one else has.” Growers can get $1.50 each for the earliest varieties of cucumbers started in heated houses in mid-March. Lacking heat, plant them two to three weeks before the last frost and consider using a row cover. Sideman warned, “Don’t put cucumbers into a 50-degree soil; they’ll stop growing.”

Montri’s tops are tomatoes – such as ‘Big Beef’; or pints of cherry tomatoes, such as ‘Black Cherry,’ ‘Sun Gold,’ ‘Sun Sugar’ and ‘Sweet Million,’ which sell for $3; or winter salad mix and spinach. He starts ‘Diva’ cucumbers on May 1 under row cover in a hoophouse; some growers are very happy with English cucumbers. Tomatoes and peppers go in on April 15.

Guzzi looks beyond having a top money maker. “Clearly it wouldn’t be sweet corn, but if you can get it to grow and produce, there’s a lot of flexibility on price on these off-season things. It seems like you can turn anything into a money maker.”

Lisa Turner’s biggest money maker per square foot is claytonia (miner’s lettuce). “You can’t sell it separately, but it’s great to add into a mix.” For a summer crop she liked the mold resistant ‘Buffalo’ tomato but can no longer get seed so is growing ‘Masada.’


Ed Person of Ledgewood Farm in Moultonborough, N.H., is a favorite supplier for many growers, because he delivers quality parts with every piece marked and all holes drilled; and he always responds to calls.

Roberts suggested buying a hoophouse from someone who doesn’t want it any more – marking the pieces as you dismantle it.

Other suppliers include Atlas Greenhouse Systems in Georgia (www.atlasgreenhouse.com); Rimol in N.H. (www.rimol.com); BFG Supply in Ohio (www.bgsupply.com); Four Season in Missouri (www.fourseasontools.com); and Zimmerman’s Welding in Versailles, Missouri (573-378-4770). The latter two make the same house, but Four Season’s is moveable. Not all are predrilled, and drilling hard steel isn’t easy. (More suppliers are listed at www.hort.cornell.edu/hightunnel/structures/sources.htm.)

Pipe benders to make low hoops and caterpillar hoops are sold at https://quickhoops.net and at Johnny’s Selected Seeds (www.johnnyseeds.com).

Recordkeeping and Crop Planning

Montri listed warm season crops for hoophouses, including tomatoes, eggplant, cucumbers, peppers, basil, summer squash and zucchini (although the latter two can go under row covers in the field; and powdery mildew loves cucurbits in tunnels).

Cool season crops include leafy cooking greens, spinach, beets, collards, Swiss chard, mustards and kale; heading greens – choys, tatsoi, Chinese cabbage and head lettuce; root crops – turnips, carrots, radishes (Montri especially likes ‘Crunchy Royale,’ ‘Watermelon’ and black radishes), red beets, potatoes (planted in March and harvested in mid-May – but only if you have a strong market); and baby leaf salad greens, including red lettuce, mizuna, arugula and ‘Bull’s Blood’ beets.

At his own farm, Montri produces three mixes: ‘Red Oak Leaf’ and ‘Green Royal Oak’ lettuce; those plus ‘Red Russian’ kale and mizuna; and those four plus arugula and ‘Red Giant’ mustard. A 4-ounce bag costs $3, two bags cost $5. “Almost everyone buys two different kinds of salad mix and some buy three,” said Montri. He grows everything separately to control what goes into the mix.

This is Montri’s schedule for producing a consistent volume of baby salad mix from March to May and September to November:

Week 1 Plant lettuce 1 (1 = first planting)
2 Plant brassica 1, lettuce 2 (2 = second planting)
3 Plant brassica 2
4 (No planting)
5 Harvest  1
6 Harvest 2
7 Harvest 1, plant lettuce 3
8 Harvest 2, Plan brassica 3, lettuce 4
9 Harvest 1, Plant brassica 4
10 Harvest 2
11 Harvest 3
12 Harvest 4
13 Harvest 3
14 Harvest 4
15 Harvest 3
16 Harvest 4

The time to produce a baby salad mix varies:
February planting – 7 weeks before the first harvest
Early March – 5 and 6 weeks (for brassicas and lettuce, respectively)
Late March – 4 and 5 weeks
April – 3 and 4 weeks

When sown between September 15 and October 15, an October cutting won’t be ready to cut again for two weeks; a November cutting, four weeks; and a December cutting, six to seven weeks. Montri and his wife harvest 30 to 40 pounds per week with OXO spring-loaded clippers. They’re also trying a salad harvester with a 6-inch-long scalloped blade. They harvest into 3- or 7-gallon flexible tubs and wash 3- to 5-pound lots in a hand-cranked salad spinner.

To produce 60 bunches of carrots for each market, they follow this schedule:

Fall planting Aug. 1-7

Winter plantings in a tunnel for spring carrots:
Feb. 10 for April 28 and May 5 harvests (11 and 12 weeks)
Feb. 24 for May 12 and May 19 harvests (11 and 12 weeks)
March 17 and 24 for May 26 and June 2 harvests (10/11 and 9/10 weeks)

Spring planting in the field:
May 1 for June 30 harvest


Growers establish prices by noting costs of production plus farm profit; other farmers’ or outlets’ pricing; by what they would pay; or by what they want to make.

Montri records crops, planting dates, number of square feet, projected yield, projected income and notes. To project yield and income for carrots, for example, he figures that 2,000 carrot seeds may produce 1,600 carrots. With12 per bunch, approximately 120 bunches at $3 each will gross $360 for that planting for that bed.

A single harvest of lettuce spaced at 8 by 8 inches in a 30- by 3-foot bed (90 square feet)
produces 4 rows with 45 heads per row, or 180 heads. Figuring 20 percent less for various losses brings that to 144 heads. To make $250 from that bed, charge $1.74/ per head. Round this to $2 per head, and the gross is $288 per bed per crop or $3.20 per square foot per crop.

Grossing $20,000 in this 20-bed tunnel means making $1,000 per bed – or growing four $250 crops per bed.

He continued with this example of pricing:

Baby salad mix
Area: 30 x 3 feet = 90 square feet
Yield = 1 pound per 6 square feet
90 square feet/6 square feet = 15 pounds
$250/15 pounds = $16.67 per pound

With three harvests per planting,
15 pounds x 3 harvests = 45 pounds/90 square feet
$16.67/3 = $5.55 per pound (for $250 range)

Other price options:
@$6 = $270 ($3 per square foot)
@ $8 = $360
@ $10 = $450

Montri also compared lettuce and salad mix based on income, area and time:

Lettuce = $3.20/90 square feet
@ 50 days = $3.20/50 = $0.06/square foot/day
@ 7.1 weeks = $3.20/7 = $0.45/square foot/week

Salad mix @ $10/pound = $5.00/90 square feet (3 cuttings)
@ 3 cuttings in 56 days = $5.00/56 = $0.09/square foot/day
@ 8 weeks = $5.20/8 = $0.63/square foot/week

These figures don’t include labor; he suggested keeping labor records occasionally to calculate the ratio of gross to net income.

Montri finished with the example of growing three crops per bed:

Head lettuce (fall and winter) @ $2 per head = $288
Baby salad mix (spring) @ $10 per pound = $450
Tomatoes (summer)
10 lbs./plant (low estimate) @ $2 per
pound (low price; more likely $3 to $5) =
$20 per plant (gross); 20 plants/bed = $400

   $288 + $450 + $400 = $1,138

Montri suggested tracking gross sales and net returns (for cost of production); product prices; quantities sold; labor (by activity); and other costs.

This and more information appear at www.hoophouse.msu.edu, which also includes a map of tunnels throughout the country; growers can enter theirs along with a photo and comments.

– J E

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