Low tunnels are ideal for the early production of many vegetable crops. They are constructed by installing 6-foot wide sheets of either slitted or punched plastic over wire hoops that are spaced about 4-5 feet apart. The cover is pulled taut over the hoops, and the edges of the cover are secured with soil. Generally, the cover is left over the plants for 3-4 weeks. The slits or holes provide daytime ventilation, eliminating the need for manual venting. Low tunnels are generally used in conjunction with black plastic mulch for weed control and enhanced soil warming. Punched covers are warmer than slitted covers and have 3/8" holes positioned 4.5" apart for ventilation. Clear plastic covering that is Un-punched and not slitted is also available.
Frost protection of 2 to 4° F is afforded by the cover, but the biggest benefit is growth enhancement provided by increased solar heating. If ambient temperatures are above 90° F, daytime temperatures might be excessive under the cover. Under those conditions, partial removal of the cover may be necessary.