Hoophouses Apex NC
Fuquay Varina, NC
Hoophouses consist mainly of clear polyethylene film stretched over steel arches. Most hoophouses serve as greenhouses, but ours also serves as workshop, storage shed, exercise room, writing room, wildlife blind and photo studio often with music in the background. In winter, a hoophouse can also function as a sun-therapy room and tanning salon. From spring through fall, it could even serve as a bedroom for overflow guests albeit good-natured ones. Have I mentioned the pleasant patter of rain on the roof?
Whether the day is sunny, cloudy or rainy, the poly film admits light that's bright enough to work by. Even on the coldest winter days, bright sunlight can raise inside temperatures above 70° F.
The point is, a hoophouse creates a wonderful space.
End-wall-mounted exhaust fans are thermostatically controlled and come in optional blade diameters from 10 to 24 inches.
In our region of New York State, with coldest winter temperatures below 0° F, it's possible to grow and harvest hardier salad greens in a hoophouse throughout the winter without artificial heaters, as proven by Maine's pioneer greenhouse-grower and author Eliot Coleman. He roots his hoophouse plants in the ground and double-insulates them by means of fabric row-covers or cold frames. In such conditions, many greens survive temperatures below freezing, although reduced sunlight tends to slow growth, sometimes to a standstill. For this type of growing, the best success comes with spinach, arugula, and mche (also known as corn salad), as well as tatsoi and other Asian greens.
Of course, with a hoophouse heater, you could grow almost any plant year-round even tender ornamentals.
Our hoophouse serves as a season extender by allowing us to germinate seed and nurture seedlings of cold-hardy plants well past the first frosts of fall, before we transplant them into our outdoor cold frame, which even allows harvest of winter-dormant lettuce in April.
Floor Prep for Other Uses
For purposes other than growing in winter (see the list on page 15), you'll need an all-purpose floor. I recommend heavy-duty landscape fabric topped with several inches of 1/2-inch crushed rock. This combination serves two main purposes: It prevents weed seeds in underlying soil from germinating, and it allows spilled water to drain into the earth, leaving your floor dry and pleasantly crunchy. Such drainage also reduces electrical-shock hazard that would be posed by a wet concrete floor.
For a 12-by-20-foot floor at a 3-inch depth, you'll need a little more than 2 cubic yards of crushed rock. A cubic yard costs only about $15 at suppliers. But delivery adds about $100 to the total. Check the yellow pages under Sand and Gravel. If you're thinking about saving delivery costs by using your own pickup truck, consider that most pickups can haul only 1/2 to 3/4 of a cubic yard, which might be dumped by a front-end loader onto your shiny truck bed.
D-I-Y vs. Pro Installation
Although handy folks can install smaller hoophouses themselves, it's often wiser to hire an experienced installer or get help from a carpenter who has installed at least one hoophouse. Besides, an experienced installer can suggest options for connectors, special features and end-wall materials.
Instruction manuals? Hoop distributors market almost wholly to professional growers that routinely put an acre or more under hoops. See our list of resources on page 17 to help you get started.
Check with municipal officials to find out if a hoophouse is allowed on your property and what the setback distances are. Setbacks are required distances from property lines and such. After obtaining a building permit from municipal authorities and maybe the blessing of neighbors within eyeshot, you can order materials.
Also you'll need to drive ground posts about 2 feet into the soil to receive the hoops, so check with officials to determine locations of underground utility lines on your property. Utility companies happily send a representative free of charge to help you map underground lines and avoid breaching them.
The ground should be virtually level, though slopes of an inch or two don't matter. Mark approximate positions of the four corners, making sure you won't damage underground utility lines when driving posts.
It's important that corners be perfectly square. To ensure this, our contractor simply plugged numbers into the Pythagorean theorem, famous for determining the distance of an unknown side of a right triangle (a2 + b2 = c2). In other words: Hoophouse Length2 + Width2 = Diagonal Corner-to-Corner2.
Using a pocket calculator for square root, our contractor determined the exact diagonal measurement. Then he used three long tape measures simultaneously to mark hoophouse width, length and one corner-to-corner diagonal, thus positioning three of the four corner posts. To determine the fourth post position, he simply restretched his tapes in mirror image of the first triangle.
He double-checked accuracy by measuring each diagonal, corner to corner. When the diagonals are equal, the four corners are square. That method is much simpler than the temporary installation of wooden batter boards at each corner and running string lines, which also requires use of the Pythagorean theorem.
Each hoop slip-fits into a pair of steel ground posts about 3 feet long and driven 2 feet deep. Use carriage bolts to fasten the hoops at uniform height to these posts. Space other pairs of ground posts at 4-foot intervals along the length of the floor, bolting all at the same height. Depending on your supplier, you'll be advised to secure ground posts vertically to a 2x10 side plank or to fasten angled steel supports.
Install the skin (poly film) on a calm day to avoid being blown into your neighbor's yard. For this, early mornings tend to be ideal. With at least one helper, pull the poly only taut enough to remove fold wrinkles, rather than stretching it tight as a drum. Installed poly expands and contracts on a daily basis.
I was amazed at my contractor's ingenuity in addressing my request that the southerly end wall be translucent. (Contrary to most advice for orientation for greenhouse growing, we needed to orient the structure's long axis north-to-south for aesthetic reasons.) Besides, as mentioned, we needed south-facing doors at least 4 feet wide to admit our lawn tractor.
A southerly end wall framed with bulky 2x4s and covered either with poly film or clear plastic panels wouldn't have allowed as much light transmission as our contractor achieved. Instead of 2x4s, he used lengths of 1-1/2-inch square hollow steel available at home centers and welded them to each end hoop at the top and to lengths of hollow steel that serve as the wall's bottom. Then he created a door-and-a-half steel doorjamb. To the steel end-wall framing, he attached rigid, translucent plastic twin-wall polycarbonate panels. (Most suppliers offer steel end-wall framing kits.)
Of course, for plant-growing purposes, end walls oriented east and west don't need to be translucent because the sun follows a southerly arc, bathing the poly throughout the day. For our north end wall, our contractor saved time and money by framing it with 2x4s and sheathing it with T-111 exterior-grade wood panels that we painted barn red.
Because the polyethylene film is a poor insulator, electric heat tends to be cost prohibitive. But a variety of fueled greenhouse heaters can protect plants on cold nights fairly economically if you also insulate the hoophouse and cover the plants.
We have only one layer of UV-protected poly film over our six hoops. It has survived the sun's rays for three winters. We're taking a chance by extending it a fourth winter, mindful of the caution of greenhouse authority Miranda Smith, Typically, you lose enough light transmission by the end of the third year to make the skin worth replacing. Also, when the plastic goes, it's dreadful it shreds into a hundred, long skinny pieces, as if a giant noodle cutter had come down from the sky.
Instead of one layer, however, Bud Peltz, of Griffin Greenhouse & Nursery Supplies advises installing two poly layers; and using an electric blower to inflate the air between them, thereby creating a pillow effect. The air layer provides a modest amount of insulation (actually increasing the R-value from 1.0 to 2.0), but more importantly, it reduces the chafing of the bottom layer of poly against the hoops. The pillow also helps the roof slough off snow. Blowers are designed to run 24 hours a day throughout the year, at a cost of about $5 per month in wattage, according to Peltz.
For ventilation, we have sidewall poly aprons that roll up a few feet as we crank a handle on a long steel pole at the bottom. Rolled up, each apron provides almost 60 square feet of ventilation. Under the sidewalls, we have long panels of mosquito screening. In each end wall, we have a household storm door with sliding, removable glass panes and screens.
With the resulting four-wall ventilation, we haven't needed exhaust fans because we avoid working inside on hot summer days. But there's even a low-tech means of reducing heat gain in summer: Over the roof, you can drape a shade cloth, available in optional shading densities from 30 to 80 percent. Just be sure to remove the shade cloth before the snow falls.
It appears that the narrowest width available from major distributors is 14 feet. Some people report success with pulling 14-foot bows into ground posts spaced only 12 feet apart. But if each bow arrives with a screw hole predrilled at the apex (for fastening of a ridgepole), that hole makes the bow vulnerable to buckling if you attempt to pull the bend tighter.
I had bows specially bent to 12 feet wide at a Connecticut supplier, but that supplier is no longer interested in dealing with homeowners who merely order six hoops and ask too many installation questions. The tighter bend gave us a taller peak height of 7 feet 6 inches, taller sidewalls and a somewhat steeper curve that helps shed snow loads. To my eye, the tighter arc is also more attractive, almost resembling a Hobbit door frame.
Cost of Materials
Barest essentials for a 12-by-20-foot hoophouse can cost about $1,000. That is, the six hoops needed for a 20-foot house would cost less than $300 themselves. The shipping, which is done on large flatbed trucks, cost us an additional $160 for up to 200 miles.
In addition to hoop cost, add about $150 for a standard boxed roll of 24-by-100-foot 6-mil polyethylene film. That amount will yield enough film for a couple of roof changes. The special connectors for poly and bows at end walls may run less than $200. They're worth it.
Other costs are entirely up to you, depending on the sophistication of ventilation, insulation and electrical hookups, as well as end-wall beauty and light transmission. For example, 4-by-8-foot panels of clear twin-wall polycarbonate cost about $70 each. Whatever you decide to save or spend on your hoophouse, chances are it will be worth it. n
Neil Soderstrom is a freelance writer based in Wingdale, N.Y.