High Elevation Gardening Web Log "Blog"

Later that evening I rechecked the weather forecast and shivered when the predicted low was actually 26 degrees, a temperature that warm-season crop cannot handle. Out came colorful sheets to cover the pots and further shelter the plants. The fabric helps by trapping heat that is radiated from the soil keeping the temperature around the plants several degrees above the low. Once the temperature was above freezing in the morning, I removed all trace of color.

Sheets are not ideal covers for plants but that was what I had on hand. Floating row covers made of lightweight spun-bonded polyester or polyethylene are a much better choice. Depending on the type and weight that you purchase, they provide between 4 and 8 degrees of protection and can be left on for weeks at a time.

In spring, a few degrees of frost protection can extend the growing season by several weeks. As many northern Arizona gardeners plant several weeks before the frost-free date of June 10th, row covers become invaluable for protecting warm-season crops. The greenhouse effect of most row covers will not only warm the air surrounding the plant but will also warm the soil, enhancing seed germination, root growth, and maturity.

Floating row covers differ from other fabrics and plastics used for frost protection as you can lay them directly on the plants. Unlike sheets, these products dry quickly and will not damage plants.

Light will penetrate row covers and, depending on the weight, allow 50-80% light transmittance. This reduction can aid transplanting tender plants. Row covers also provide wind protection for seedlings.

Row covers are an environmentally friendly way to prevent insects and other pests from damaging plants. They are great for keeping flea beetles off radish, turnip, arugula, broccoli and cauliflower.

Cool-season crops can handle light frost once they’ve hardened off. I didn’t cover my peas, spinach, lettuce, kale or argula and they showed no ill-effects from the cold. But, cool-season seedlings can suffer from freezing temperatures. Row covers can provide the protection they need to become established in spring.

Row covers can be used for several seasons but eventually will be degraded by UV radiation. You can extend their life by folding and storing them away from sun and moisture when not in use.

Floating row cover is often called by the manufacturer's name such as Typar, Agri-Pro or Agribon.

The down side to row covers is that pollination of crops such as melon, squash, and cucumber will be prevented unless the cover is periodically folded back to expose flowers to insects.

Floating row covers are not practical in windy neighborhoods. And they are not inexpensive.

But floating row covers are much easier to use than a collection of old cotton sheets and nursery pots. My garden survived this frost but may not be so lucky next time. For high elevation gardeners, it is not a matter of if a frost will occur but when.

By Hattie Braun
The author is the Master Gardener Program Coordinator for Coconino Cooperative Extension. If you have a gardening question, call the Master Gardener hotline at (928)774-1868 ext. 19.