Stetson - Extend Your Garden Season: Row Covers and Mulches: Storeys Country Wisdom Bulletin A-148

by Fred Stetson

Season extending has come a long way since I made my first cold frame more than twenty-one years ago. I can still remember that leaky, damp, rickety box, with the slanted front, the old, discarded window sash. Many gardeners continue to fashion cold frames from whatever materials they can find. Others rely on old standby covers, such as hot caps. Or perhaps they simply plant against the shelter of a warm, south-facing wall. This book will advise you on how to take advantage of a relatively new technique: row covers. You will find two main kinds of row covers: floating and plastic.

Floating row covers are soft, white garden blankets made of a lightweight, permeable material designed to minimize the effects of frost, harsh sun, and driving rain. They have the added benefit of protecting against insects. Because these row covers require no supports, they are known as floating row covers. Another kind of row cover is a thin, perforated or slitted plastic laid in the form of a tunnel and supported by wire hoops. Depending on the plastic, these tunnels provide variable frost protection and can generate heat often in excess of 100F. These row covers can also help warm-climate gardeners extend their growing seasons into periods when its too hot, rather than too cold. Growers use tunnels of opaque plastic or shade netting to reduce temperatures.

Plastic over wire hoops, weighted with boards

Hot caps

Before getting into more detail about row covers, here are suggestions for using some old-fashioned season extenders that remain a popular, low-cost choice for many gardeners. Cold frames, plastic cones, hot caps, plastic milk jugs with the bottoms cut away, hay bales, newspapers, blankets, plastic-wrapped wire frames, and even inverted grocery bags with their edges turned down and weighted with soil, all work well in certain situations.

A popular commercially made product is Wall-O-Water, which is an 18-inch-high, tee-pee-shaped plastic tent that protects plants from hard frosts. Wall-O-Waters are self-standing, 18-inch-high circular belts of plastic tubes filled two-thirds of the way with water. The first time I tried them, I noted a one-hour temperature gain of 14F around my tomatoes. To keep temperatures from getting too hot, add more water to the tubes to make them more turgid and open at the top. With less water, their tops lean in, forming a teepee.

Cold frame

Milk jug with bottom removed

To protect tomatoes and other tall, heat-loving plants from frost or wind, erect a cage around the plant, then wrap the cage in plastic or fabric. Make the top removable, so you can close it at night and vent the cage in the day.

Garden suppliers also sell high tunnels or tunnel greenhouses. About 4 to 6 feet tall, these are larger, more-permanent season extenders. Usually supported with PVC pipe, wood, or some other inexpensive framing, they generally measure 12 to 16 feet wide and 12 to 24 feet long. They may be covered with new, durable plastics such as Polyweave, an 8-mil thick, fiber-reinforced polyethylene or Tuffbell 900N, made from polyvinyl alcohol. A less-expensive choice is 6-mil polyethylene. Companies often guarantee their materials for a specific number of years. As one season progresses to another, some gardeners such as New England author Eliot Coleman, systematically rotate high tunnels from plant to plant.

Wall-O-Waters

Wrapped tomato cage

Celia Hackett of South Hero, Vermont, extends her season by laying 4x8-foot pieces of lattice, supported by cement blocks, over her lettuce beds. With this shading, she grows lettuce during warm spring or early summer days.

In some respects, the term, extenders, is a misnomer. More than adding a few weeks to the start or end of a season, extenders actually modify the growing climate. They help protect from not just frost but wind, pests, even rain and snow. A driving thundershower pounds the soil and splatters plants, but not if theyre beneath covers or plastic tunnels. In university field tests, plants grown beneath floating row covers yielded more vegetables and fruits and more vegetables and fruits earlier than unprotected plants. In New Hampshire and Oregon, cantaloupe production doubled. Further, covers enable you to grow melons and other heat-loving plants in zones where, without protection, they would not survive or reach maturity. Whats more, bigger and sweeter varieties are possible with covers.

You may purchase, primarily through mail-order catalogs, a variety of protective plastics, each designed for specific tasks or conditions. For example, floating row covers are available in numerous weights, sizes and thicknesses. In general, the thicker, heavier covers offer more frost protection than lighter, thinner covers. They also generate more heat something to watch out for as spring days lengthen and sun intensifies.

Floating Row Cover

The first time I used floating row covers, I was not trying to extend my gardening season I was trying to save it. Ground hogs had gnawed our young squash, broccoli, and eggplants down to stubs. They even chewed the tomatoes and my wifes marigolds and zinnias. In retaliation, I dragged long stretches of white floating row cover out of our shed and draped them over the plants. Soon, they revived. Tomatoes, which had not been bitten hard, pushed the cover upward. Within a week, their leaves darkened to a rich green. Tall stems were outlined beneath the thin fabric and crystal beads of condensed moisture dotted the covers undersides.

What exactly are floating row covers? Theyre lightweight, nearly translucent, synthetic lawn and garden fabrics of various sizes. In thickness, color, and texture, they resemble the white inner linings sometimes found in shirts or jackets. They vary in weight from .3 ounces per square yard (an extremely light material designed for insect protection) to 2.0 ounces per square yard (an extra heavyweight cover to fight frosts, freezes, and other damaging winter effects).

Weight and material are key factors to consider when selecting a cover. In general, the lighter the material, the more light transmission, but the less frost protection. For example, .3 ounce fabrics offer no frost protection, but they are effective screens against most insects. A 2-ounce cover provides more than 8F of frost protection, but only transmits 30 percent light. As covers increase in weight, they also increase in cost another factor to consider.