Season Extension Techniques

 Floating Row Covers

Floating row covers consist of large sheets of lightweight fabric placed over single or multiple rows of a crop to provide some protection against frost.  The covering may be made of clear polyethylene, spun bonded polyester, or spun bonded polypropylene.  The fabric comes in different weights:  the heavier the material, the greater the frost protection.  Row covers can be  used in the fall, as well as early spring, to extend the season.  When used to protect spring crops, covers are removed before the plants mature, while fall frost protection necessitates leaving the covers on mature plants.

Low Tunnels

 Low tunnels with a plastic covering do not permit rain to penetrate so they are often used in conjunction with black plastic mulch and drip irrigation.  Low tunnels also trap heat so that daytime temperatures can rise to dangerous levels within the tunnel making ventilation essential.  Various modifications to the original low tunnel design and covering have been made to allow for increased air circulation.  These include pre-cut slits in the covering material, a “seam” running down the center top of the tunnel that can be open on hot days, raising one side of the tunnel covering, and the double-hoop system that allows for raising and lowering both sides.

 High Tunnels

 The field greenhouse of the past is now generally called a “high tunnel” or “hoop house.”  A high tunnel is a hooped frame of walk-in height covered with plastic.  Tunnels may have a rounded Quonset shape or they may have the peaked roof of a Gothic style high tunnel;  They may be a single stand-alone house or form multi-bay tunnels.  High tunnels can be erected as moveable structures that are relocated to a new site each season, or they may be placed in a more permanent location.  If the tunnel is to remain in one location, it is important to remember that salts can build up in the soil from fertilizer applications.  Plan on removing  the plastic cover as needed to allow natural precipitation to flush the salts from the soil.

      For more information, call Shad Baker, Letcher County CEA for Agriculture and Natural Resources at 633-2362, 634-7799 or email at

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