Stretch Your Growing Season
By Kris Wetherbeey

Push the limits on both ends of the gardening season by using row covers, cold frames, and other plant protection techniques.

During the years my husband and I were market gardeners, there was always an unspoken challenge to be the grower to produce the first ripe tomato or melon of the season. At times that took a bit of effort given the occasional late spring frost that would sneak up on us, or a sudden spring hail storm. At the other end of the growing calendar, an early, unexpected fall frost had the capacity to drastically shorten the harvest season. Even without crop-damaging temperatures, our chilly Pacific Northwest spring and autumn nights cooled things down to the point that crops were sometimes slow to ripen. We came to rely heavily on simple season extending strategies and plant protection devices to shield our crops from weather extremes and extend our growing season by weeks or months on both ends.

We are no longer market gardeners, but we’ve retained the desire to get a jumpstart on our garden fresh produce. And we still look forward to the early arrival of our first vine-ripened tomato. Although our kitchen garden has shrunk considerably, many of the season extending tools and techniques we used are still in place today.

Ground rules

Whether commercial or homemade, most plant cover-ups are designed to trap the sun’s heat, thereby protecting plants from weather extremes while encouraging plant growth. The degree of protection and heat gain varies among the type of season extender and material used. For example, a plastic milk jug used to protect a seedling offers only a degree or two of protection at night. But an insulated cold frame with a framed double-pane glass lid can offer added nighttime warmth of up to 10 degrees or more.
On a sunny winter day, temperatures inside an airtight cold frame or other season-extending device can quickly climb above 100 degrees Fahrenheit. Excessive temperatures can be kept in check by venting your setup so that excess heat can escape. Typically the vents should be closed by late afternoon to retain that heat gain throughout the night.

Season extenders not only help protect plants from cold temperatures, frost, and drying winds; they can also be used to start seeds, harden off plants, warm up the soil, grow cool-weather crops, speed up fruit production, protect and prolong blooms on fall-flowering plants, and extend the harvest season. Some can be used to help cool things down in southern climates, where hot weather gardening can be more of a challenge than chilly temperatures. A portable frame covered with lath strips or shade netting will help curb the heat around seeded beds, young transplants, and heat-sensitive flowers and vegetables.

Individual plant protectors

When you have only a few vulnerable plants to protect from a light frost, the simplest cover-up can often be found inside your own home, such as an old sheet or blanket, piece of burlap, bottomless cardboard box, coffee can with both ends removed, or the handy plastic gallon milk jug with the bottom cut out.

Commercial hotcaps work well when days are sunny and nights are clear. These individual plant covers act as miniature greenhouses by trapping heat from the sun. Designs vary from wax paper cones to water-filled plastic tepees, such as Wall-O-Water and Teepee Kozy Coats. They speed germination and plant growth and protect young seedlings from low nighttime temperatures.…

Plastic Mulches

Black plastic can warm soil temperatures from five to seven degrees Fahrenheit to a depth of two inches. Clear plastic heats up soil temperatures even more—up to 14 degrees—but its transparency allows weeds to grow beneath the plastic. Green plastic mulch is just as effective at warming the soil as clear mulch, but without the weed growth. Brown plastic warms the soil better than black and is a more effective weed deterrent than green plastic.

For maximum solar gain and weed control, infrared-transmitting mulch (IRT) combines the best of both clear plastic and black plastic, and is especially useful on early spring crops. The hot ticket for southern climates, however, is white-on-black plastic mulch. This relatively new mulch reflects most incoming radiation, so soil stays slightly cooler but weeds are still kept in check.…

Floating Row Covers

Made of spun polyester, polyethylene, or polypropylene, these fabric-type covers vary in weight, thickness, and degree of protection. They are also permeable to light, water, and air. Some only allow 50 percent light transmission and protect plants down to 24 degrees, while others allow up to 90 percent light transmission with frost protection down to 27 degrees…

Kris Wetherbee is a garden writer living in Oakland, Oregon.

Photo credits: Floating row covers over hoops by Shepherd Ogden. Kozy Coat teepee by Rita Pelczar.
 

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