When the days begin to shorten and the nights begin to cool, many gardeners are sorry to see the summer go, even as we hustle to harvest and preserve the last of our warm-weather crops. While most hot-weather plants will give up at the first glance of frost, many vegetables thrive once temperatures drop in the fall. And with numerous ways to protect them from the chill, the harvest can continue — when conditions are good — right through the winter.
The secret to season extension is not to attempt to create an endless summer, but in working with the seasons so that crops are sown, grown and harvested as nature intended.
Floating row covers
These come in a variety of lengths, widths, and weights. Lightweight row covers might be considered windbreakers for plants. Made from thin, white, woven material, they can be laid loosely atop planted rows or stretched over the hoops of low or high tunnels to keep frost and bitter wind off tender plants while allowing light, water and air through.
When using row covers to protect your plants, use the minimum weight required for the tenderness of the plants you grow. As fabric weight increases, light penetration decreases, and all plants need light to thrive. Each layer of lightweight row cover will increase the temperature under cover by 4–8 degrees while decreasing the light that reaches your plants, so it’s important not to stack too many layers.
Heavyweight frost blankets are great for short-term protection (such as a sudden cold snap or an especially frigid winter night), but shouldn’t be used to protect actively growing crops for long periods, as they block out too much light. When the temperatures drop, your plants may be better served by a tunnel covered with plastic (see below).
Tunnels or hoop houses
These small-scale, unheated greenhouses can be scaled up (“high tunnels”) or down (“low tunnels”) according to your needs and space. “If you’ve got the room, this is the way to do it,” says Jonathan Krausert, a Rose Park gardener.
Both high and low tunnels are built by bending flexible tubing (such as rebar, PVC or aluminum pipe) into half-moon arcs, called hoops. The length of the tubing you use will vary depending on the desired height and width of your hoop house.
After cutting them to length, bend the tubes into hoops and drive the ends firmly into the ground. Space the hoops 3–4 feet apart, and cover the entire structure with floating row cover, clear plastic, or both (depending on the tenderness of the plants growing inside and the time of year they’re growing).
When sealed against the elements, the temperature inside tunnels can be as much as 30 degrees warmer than the air outside, which is excellent for starting seeds in the spring — and creating a balmy growing environment in the dead of winter. However, these dramatic differences in temperature require that hoop houses covered in plastic be “vented” on sunny days, even when it’s cold. Venting a hoop house simply means partially rolling up and clamping one wall of the house to the hoops to allow excess warmth to dissipate so plants don’t overheat.
These are bottomless boxes placed directly on top of the soil and lidded with clear glass or plastic that can be penetrated by UV rays. They are often made of wood, but can also be built using other kinds of materials. Like tunnels, cold frames are usually used to protect cold-hardy plants from extreme winter conditions and need to be vented by propping the lid open on sunny days.
Cold frames are often designed with one side taller than the other, which angles the lid up towards the sun. The clear top allows sunlight in and traps residual warmth, protecting hardy and semi-hardy plants from freezing in the ground. For added protection from cold, semi-hardy plants growing inside cold frames can be mulched, and snow pack can be used outside of the frame as an insulator (though snow should be brushed off the lid). In addition to serving as protection in fall and winter, cold frames, like tunnels, can be used to start seeds in the spring, allowing a jump on the warm-weather growing season.
Rooted in the fall
Some hardy and semi-hardy vegetables can be mulched or protected to continue the harvest into winter. Here’s a short list: Cabbages, cauliflower, broccoli, Brussels sprouts, kale, collards, kohlrabi, mustard greens, bok choy, carrots, turnips, parsnips, radishes, some types of beets, spinach, arugula, many lettuces (particularly the loose-leaf varieties), mizuna, sorrel, tatsoi, chard, mache (“corn salad”), claytonia and bunching (green) onions.
Not that warm-season crops can’t be coaxed into producing for a few additional weeks in the fall. Doing so is only a matter of protecting them from frost and, perhaps, raising the temperature of the environment in which they grow by a few degrees.
But the crops that are plentiful and truly delicious during the chilly months are those that love cool, wet weather: members of the mustard family (cole crops or "brassicas"), root vegetables and a vast assortment of greens.
Cold-weather edibles have the unfortunate reputation of being uninteresting, which may actually be code for unappreciated or unfamiliar. The versatility and varied tastes and textures of the hardy veggies rival that of summer crops, but without a long-standing tradition of winter gardening (and with the accessibility of out-of-season crops at the grocery store), many of us are simply unaware of the options. (See box.)
Getting started • Season extension can be as simple or as involved. The easiest method is to plant seeds that will overwinter. Once the summer garden is finished, you simply clear a space in your garden plot and spread seeds of vegetables that love cool weather.
While a few may germinate during the last weeks before hard frost, most of these seeds will simply go dormant, sleeping through the winter and sprouting in early spring when they sense that the time is right. Planting a fall garden requires "a lot less input from me," says Carly Gillespie, community educator for Wasatch Community Gardens.
It’s a more casual gardening time, she says, which takes a lot less maintenance, as seeds are easy to sow, and most of the pests and weeds that invest summer gardens are a non-issue in the fall.
Thanksgiving harvest • If your goal is to harvest fresh vegetables throughout the fall and early winter, slightly more work in terms of planning and preparation is involved.
To begin, you will need to know the first average frost date for your area and work backwards to determine when to plant seed in order to harvest fully mature crops. For example, if your first average frost date is Oct. 15 and the plants you want to grow need 90 days to mature, those seeds need to be planted no later than mid-July and provided with some shade, which will lower soil temperatures and aid germination.
However, if you haven’t planned that far ahead this year, all is not lost. Many varieties of cool-season crops have shorter growth cycles, and most need cool, wet weather to sprout, so you can easily plant a fall garden now and be harvesting your veggies around Thanksgiving.
Global warming, one garden plot at a time • Besides planting cool-season vegetables to extend the gardening season into fall, many season-extending gadgets are easy and inexpensive to assemble. These can protect your crops from wind and frost (the true garden killers) and raise the temperatures of your beds by a few degrees — which is often all plants need to survive winter weather.
Professional growers use numerous techniques to protect their crops, many of them involving artificially temperate environments created to grow vegetables out of season. For the home grower, these technological marvels can be impractical as well as prohibitively expensive.
However, three season-extending options, built from simple, easily accessible materials, can harness the power of the sun to protect hardy crops: row covers, tunnels and cold frames.
How you use these season-extenders is open to creative interpretation, and whatever your approach, you will come out ahead. Jonathan Krausert, of Rose Park, is an urban homesteader who grows 90 percent of the vegetables and 80 percent of the fruit that his family eats every year. He’s gotten some of his best ideas from peering over the fences of other passionate gardeners.
Warm-weather gardening is a race against time, but ample opportunities exist to continue growing and harvesting fresh, home-grown food throughout the year: All it takes is a new perspective on what it means to grow a vegetable garden in Utah.
Take back the winter! With some foresight, minimal planning, pocket change, and personal investment in bringing healthy, flavorful food to the table, you can grow what you eat all year long and reward your palate with the varying flavors of the seasons.
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