Freeze damage to a young cucumber plant

A question I often ask tour groups at the Noble Foundation Horticulture Center is, "Why doesn't Oklahoma have a horticultural industry rivaling that of California's Central Valley?" Some common responses include lack of irrigation, markets, labor, poor soil and a short growing season. Although all of these have some legitimacy, they are not paramount. The single greatest deterrent to sustainable horticulture in Oklahoma is extreme weather.

The Horticulture Center was developed in part to address the problems gardeners face in extreme weather regions. During the mid-1990s, our emphasis shifted from researching and demonstrating the benefits of permanent raised beds to addressing weather-based problems, primarily temperature-related ones.

In response to these problems, horticultural researchers have joined forces with plastic film manufacturers to develop protective covers for both commercial and hobby gardens.

There are two types of plastic crop covers. The first consists of polyethylene film supported on frames or hoops to form a tunnel over a row or bed. The second is a fabric-like polypropylene material that floats or can rest directly on the crop. The edges of both kinds of cover are anchored in the soil to combat wind.

Fibrous nature of floating covers

The polyethylene row covers are generally cheaper, but more labor-intensive because of the support structure. They create higher daytime temperatures, which is desirable for early- and late-season production, but require venting to control heat buildup on warm, sunny days. Some manufacturers offer row covers with preinstalled slits or circular perforations for automatic venting. Some even offer pigmented (opaque) covers for added cooling. The standard width for row covers is 6 feet.

Because of their porous, lightweight design, floating covers are self-venting and usually don't require a support structure, making them more versatile than row covers. Their width varies from about 6 feet up to about 60 feet, large enough to cover an entire garden. However, if whipped by high winds, floating covers can injure young seedlings. If your garden is exposed, consider using a support structure or erecting a windbreak.