Extend the Season, Increase Your Harvest
by Scott Vlaun

As every organic gardener knows, once you've experienced the profound joy of picking fresh produce minutes before preparing it, you can't get enough. What many organic gardeners don't realize is that if you can eat fresh food from your garden for part of the year, you can probably have it all year round, or nearly so. By selecting the right varieties and using some simple techniques, most North American gardeners can enjoy the lively flavor of fresh food year-round, especially nutrition-packed leafy greens, without using supplemental heat.

While certain garden plants such as basil and beans will "give up the ghost" with the first light frosts of fall, other garden staples like kale, brussels sprouts, and tatsoi seem to thrive on the cool, crisp weather of autumn, and will survive hard frosts unscathed. Even within specific crop groups, certain varieties are bred to be more cold hardy than others. Many have been developed over decades, or even centuries, of seed saving in the coldest climates. Among the cabbages, it's hard to find a hardier variety than January King. Reine de Glaces (King of the Ices) is a great cool weather lettuce and True Siberian is a fine kale for growing well into winter. See below for other varieties that are well suited for late and early season cultivation.

• Arugula
• Mustards, especially Tatsoi, Komatsuna, Mizpoona, and Red Giant
• Kale, all especially Red Russian and True Siberian
• Broccoli Raab
• Radicchio, Early Palla Rossa
• Beets, all
• Cabbage, especially January King
• Brussels Sprouts, Long Island
• Chard, all
• Cauliflower, All the Year Round
• Collards, all
• Leeks, especially Scotland and Winter Giant
• Lettuce, especially Reine de Glaces, Rouge d'Hiver, Brun d'Hiver, and Val d'Orge
• Peas, all, especially for early season
• Spinach, especially Bloomsdale
• Radishes, all
• Rutabaga, Joan
• Turnips, all

Any plant, whether tender or hardy, can benefit from the creation of microclimates. Cold frames, cloches, tunnels, and row covers can all help the most cold-sensitive plant survive an early, light frost, or help a bed of hardy greens overwinter in the coldest of climates. The easiest way to provide protection for your plants is to simply cover them. Even throwing a blanket over them on a cold night and removing it during the day can extend the season by two weeks or more. Floating row cover is especially designed for the task and allows light and moisture to penetrate without weighing the plants down too much. It is especially useful for plants that grow from the center, so that the outer stronger leaves can suspend the cloth while the delicate inner leaves are free to grow. All the hardy greens fall into this category. For plants that grow from a meristem, or the tip of the plant, it is better to support the row cover with hoops or cages to prevent impeding the plant's growth. A thick mulch of loose straw under the row cover can also help support the plants and provide extra insulation.

Another way to create microclimates for your plants is using cold frames. The beauty of the cold frame is that they open for easy access to the plants for tending and harvesting and for sun exposure on warm days. Face them to the south for maximum exposure, and even when they're open, they shelter the plants from the wind and provide a beneficial climate; a light inside color also helps to reflect light. A downside to cold frames is that they can overheat on warm sunny days if you forget to open them. Automatic vent openers are a way to solve that problem, providing a more consistent environment for the plants and extending the season three–four weeks or more.

Hoop houses or tunnels can also be used to great advantage for extending your growing season into the cold of winter. From small "off-the-shelf" tunnels of row cover or plastic, to custom made larger tunnels of bent wood, metal, or plastic pipe covered with greenhouse plastic, to large commercial "walk-in" hoop houses, all can add weeks to the season. Combined with mulch, and row cover directly covering the plants, and even a thermal blanket or tarp over the plastic at night, all but the coldest climates can be tamed for a year-round harvest.

As days get shorter and light levels drop, growth will slow dramatically on most plants, even when they are protected from extreme temperatures. This doesn't mean that you can't dig through the snow and harvest some tatsoi and parsley in the dead of winter; it just means that it won't put on much biomass in the shortest, coldest days. If your timing is right in the fall, and the plants become well established, but not too mature or leggy, you should see rapid growth begin in the first warmer, longer days of spring. This is called overwintering, and it is the best way to get an early spring crop of many varieties of greens. Spinach and kale are two of the best overwintering crops but, depending on your climate, you might have luck with many other cold-hardy greens and brassicas. It is wise to experiment with different varieties and timing to see what works best for you.

Just as farmers have done for millennia, try saving seed from some of your most successful overwintering plants. Many of the cold hardy brassicas are prolific seed producers and are easy plants from which to extract seed. Usually they will produce mature seed by early summer, which you can sow that fall to start the cycle all over. Armed with handfuls of your own seed, you can plant in succession every two weeks or so throughout late summer and early fall in beds that have been cleared of summer crops. You'll not only be rewarded with a fall season rich with flavorful, nutritious green vegetables, but if you try some of the techniques outlined above, you might just find an oasis of lush green food when the snow melts in the spring.

For more information on extending the growing season, read Four Season Harvest by Eliot Coleman.