Regional Gardening Reports :: National Gardening Association

In the Garden:
Upper South
February, 2006
Regional Report

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Season-extending systems allow you to grow fresh lettuce, kale, and other cool-season crops almost year-round.

A Sheltered Life

Growing vegetables out of season in a protected environment is a concept that has been around for centuries, yet not nearly enough gardeners avail themselves of the possibilities. I'm not talking upscale or difficult, no conservatories or tomatoes here, but having spinach, kale, lettuce, other greens, and a few hardy herbs for much of the winter with only modest effort and expense. Although, at its most basic, this sheltered environment can be done with only a few boards and an old window, an assortment of new materials and designs in the last several decades has expanded the ways that cool-season vegetables can be overwintered.

Cold Frames
The classic cold frame looks like a box but with one side higher than the other. The bottom is open and sits directly on the soil. The top, which may be hinged or lifted off for access, was traditionally glazed with glass. Dimensions are usually 2 to 3 feet wide and 3 to 6 feet long. With the addition of a heating cable buried in the soil, the unit is then referred to as a hot bed.

What's new is the use of twin-wall polycarbonate panels instead of glass, as these offer improved heat retention, plus the plastic is not as easily broken. In addition, the twin-wall is easy to use as side panels as well as the top, so plants receive more light. The panels are UV-stabilized and generally have a 10-year warranty. The framework holding the panels is usually aluminum, but wood-framed ones are also available. Cold frames made with the twin-wall are widely available from garden and greenhouse supply catalogs. Prices are in the $75 to $150 range.

The downside to the aluminum-framed models is that because of their light weight, they blow away if not anchored well. I've also had problems with the panels popping out of the frame. Wood-framed ones have the advantage of weight, but eventually the wood rots, even when made with cedar.

One of the simplest (and rather ingenious) protective plant devices resembles a clear plastic umbrella. The "handle" is inserted into the soil, and tie-down eyelets and anchor pins keep it from blowing away in all but the worst storms. There is usually a "door" on the side that zips for access. Sizes range from 29 to 49 inches in diameter, at a cost of between $10 and $30. Obviously not heavy-duty, but these are handy to keep around for protecting either individual plants or small plants for several weeks at the beginning and end of the growing season.

Another option available in catalogs resembles a miniature pup tent, with a cover of clear plastic that fits over the metal or PVC frame. Usually about 4 x 6 feet, some designs have a zip-open window on both sides that includes a fabric screen as well as the plastic. This makes the unit useful year-round by keeping insects and birds out of crops and providing shade for summer lettuce crops. Prices start at $50. The biggest downside to this type of unit is that the plastic cover eventually wears out and a replacement is not available.

Hoop Tunnels
With the advent of clear, flexible plastic sheeting, the hoop tunnel has become the most widely used technique for sheltering horticultural crops by commercial growers. It's not difficult for home gardeners to create scaled-down versions. Wire hoops, either homemade from #9 wire or purchased, work well for beds 30 inches or less wide. Purchased steel-tubing hoops are available that make very stable, long-lasting frames, particularly when combined with plastic or wood raised beds. The cheapest, easiest method is to use PVC pipe an inch or less in diameter. I use this system in raised beds, cutting 16-inch lengths of rebar, inserting half their length into the soil on each side of the bed, cutting the PVC to the desired length, and placing the PVC over the exposed rebar. Thirty inches or so is a good height for a bed, with pipes spaced 2 feet apart. This framework is covered with plastic sheeting. Specialized garden clothespins or PVC pipe snap clamps hold the plastic in place.

Add Garden Fabric
Laying a specialized garden fabric cover over the crops under the hoop or cold frame cover further enhances cold weather protection. This white, non-woven fabric allows light transmission and is porous to air and water. Different weights are available; for winter protection, use the type designed to protect to 24 degrees F.

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