Early Crop Production in Unheated "Poly Tunnels"

While some growers are going into greenhouse vegetable production in a big way, with computerized, controlled environment greenhouses and soilless growing systems, others are slowly getting involved in "greenhouse farming" using conventional coldframes covered with a single layer of poly, often referred to as poly tunnels. Since no automated heating or cooling is used, this allows a low cost way of entering the specialty produce business that can yield an excellent return on investment.
  Growing early crops in poly tunnels has been popular in England for a number of years, and is just now catching the interest of U.S. farmers looking for ways to diversify their farming operations. Crops most suited for poly tunnel production include tomatoes, peppers, and squash, especially the green and yellow zucchini varieties.
  The objective with poly tunnel production is to beat the local field production by two to three weeks, thereby taking advantage of the higher prices available at that time due to the pent up demand for fresh, "locally grown," "just picked from the farm" produce.
  Construction of the tunnel should begin a month or so prior to planting into the ground so that the soil can be warmed up and so it can be worked prior to planting.
  Typically, a 15' x 96' coldframe is used since it offers a good, workable size at a fairly low cost per square foot. The coldframes are quite easy to install, taking about one full day for two people. A single layer of poly film, preferably IR film which will help retain the heat at night, is used to cover the coldframe. The poly film can be attached by batten boards or batten tape, or an aluminum locking device may be used. This is more expensive, but makes covering and uncovering the coldframe much easier. Since it is a job that will be done every year, this additional cost is a wise investment.
  Poly film is also used on each end, and can be attached a number of ways, with care being taken to allow easy opening and closing of the entire end for flow-through ventilation. It is possible to install roll up side curtains, which add cost, but will make ventilation much easier and prevent over heating of the tunnel when the sun shines.
  Once the tunnel is up and under cover, it is time to begin the seedlings. For early squash production in Northeastern Ohio, seeds would typically be planted near the first of April. They are started in Jiffy pots filled with a seedling mix such a Fison's LCI. These need to be started in a heated greenhouse, or indoors under lights, where proper germinating temperatures can be maintained.
  Once showing their second set of true leaves, usually three to four weeks after seeding, they are ready to set out into the tunnel. The ground should be worked thoroughly, soil tested, and any necessary fertilizers added. Drip irrigation lines, if used, should also be laid at this time.
  Ground cover is now placed over the soil with holes cut to accept the transplants. The ground cover should be the woven kind that will allow water to seep through, but will prevent weeds from coming up. This can be purchased in 15' widths, and may be used for more than one year. Once the seedlings are transplanted, they should be watered in.
  Spacing for squash in a poly tunnel can be somewhat closer than outdoors, since, with woven ground cover, no cultivating needs to be done. With two plants per "hill", row spacing on 4' centers and approximately 3' between rows, a 15' x 96' tunnel will hold 200 plants.
  It is important to keep a close watch on the temperature in the poly tunnel as well as the local weather conditions. A closed up tunnel can reach extremely high temperatures on days when the sun is shining brightly and damage to plants can occur quickly. The ends must be opened, or the sides must be rolled up so that adequate ventilation can take place.
  As the plants begin to grow, care must be taken to water regularly, and fertilize when needed. Foliar feeds can be used if desired. Insect control is no different than outdoors, and pollinating of blossoms is accomplished the same way as outdoors, by wind for some crops, and bees or insects for others.
  Once all danger of frost is passed, and nighttime temperatures are not dropping below 60 degrees, the poly cover can be removed. Harvesting should be done daily, and all poorly shaped squash should be picked off along with any broken leaves. With the close plant spacing, good sanitation practices are especially important and will help to increase overall yields.
  Yellow squash and green zucchini can produce abundantly, and prices in May and June can be as high as $.75 per squash. When harvesting, handle the squash with care to maintain their just-picked appearance. When presented with quality squash, two to three weeks earlier than field grown squash, produce buyers will have a hard time turning you down!