Season Extension - Getting More From Your Garden
Many people garden in places where it is either too cold or too hot for good plant growth part of the year. On this map only the area in dark brown is warm enough to grow most vegetables year round. Going further north or to higher elevation usually shortens the growing season. But, there are several relatively simple things that gardeners can do to keep growing food as the weather gets colder.
One of the most obvious and probably the most effective technique is to select plants that have evolved some resistance to cold. This is an area where leaf crops shine. Kale, collards, turnip, mustard, and beet greens, Austrian winter peas, parsley, chard, garlic chives, spinach, Chinese cabbage, and a dozen other leafy greens can tolerate some freezing weather.
A second strategy is to grow plants that mature quickly enough to harvest before freezing weather sets in. Again leaf crops lead the way. Where sweet corn or tomatoes may take 80 days or more of warm weather to mature, some leaf crops like amaranth, quail grass, tatsoi, spinach and arugula can be ready to eat in just thirty days.
Some multi-use plants like sweet potatoes and pumpkins can produce a good crop of greens even though they don’t have enough warm weather to produce their primary food outputs. While there are clearly not enough warm days to produce second crop of roots, we can always beat the cold weather by growing a crop of tender sweet potato leaves after we harvest the roots. The leaf crop sprouts up from little sweet potatoes we missed so we don’t need to plant anything.
Another strategy for extending the growing season into cold weather is to create micro-climates with more favorable growing conditions. The simplest of these is place a thick layer of mulch around your plants to insulate the soil, holding the ground’s warmth for longer.
Floating row covers, made from spun polyester, can insulate sensitive plants and provide a few more degrees of protection from cold damage.
To protect your plants against really cold weather you probably need to employ the “greenhouse effect”. This is when temperature rise because visible light passes into an area easier than the reradiated infrared energy passes back out. This effect is why greenhouses can grow plants in cold weather. It is also the primary cause of climate change as increasing carbon dioxide levels in the atmosphere blocks escaping infrared energy more efficiently than it blocks incoming visible light. Gardeners can employ this effect in anything from full size greenhouses to simple cold frames.
Cold frames can be made with old windows, but greenhouse plastic is ideal. This is usually 6 mil UV treated polyethylene designed to last at least 4 years. Regular plastic sheeting beaks down quickly in sunlight. If you garden in a region that needs protection from the cold, greenhouse plastic is probably available.
We often make cold frames with bales of hay or straw. This insulates the plants from the wind and the hay or straw can be used as mulch later. Putting your cold frame against the south wall of a building offer more protection without sacrificing sunshine. If you can afford to build a coldframe large enough to walk into you can work with your plants a lot easier.
A variation on the cold frame puts about 16 inches of horse manure or fresh compost below the soil in the frame. This is called a “hotbed” because the manure or compost warms the soil above it as it decomposes.
If your garden is arranged in permanent beds you can convert them to cold frames by pulling a layer of greenhouse sheeting over hoops made from plastic plumbing tubes. We usually use ¾ inch tubes set about every 4 or 5 feet apart.
An interesting, though more complicated, variation is the “pit greenhouse.” A few feet below the surface the soil temperature remains relatively constant year round because of the enormous thermal mass of the soil. This is why caves have a constant temperature. You can take advantage of this natural phenomenon by putting your cold frame or greenhouse over a trench or pit that is 4 or 5 feet deep. You will need to stabilize the walls and assure good drainage to make this idea work.
In much of the tropics and during the heart of the summer in the temperate zone gardeners may struggle with too much rather than too little solar energy reaching their plants. Here in northern Florida, for example many gardeners consider the time between May and September too hot to grow vegetables.
There are two good strategies for extending the growing season into very hot sunny weather. The most important of these is choosing tropical plants that have evolved a resistance to high temperatures. Your spinach and lettuce may get bitter and go to seed; your tomatoes and squash may stop setting fruit; but tropical greens like Okinawa spinach, jute, and roselle will thrive in the heat.
The second strategy for beating the heat is using shade. Shade is especially important for young plants until they can develop a sturdy root system.
Probably the best material for shading plants is shade cloth intended for that purpose. Wherever greenhouse supplies are sold shade cloth is usually available. It allows rain and enough sunshine to pass through for good growth but reduces the intensity of the sunlight by about 40%. Actually, there are different grades of shade cloth that block out different amounts of sunlight, but the 40% shade cloth is widely available and generally works well.
The same growing beds or cold frames that had clear sheeting stretched over it when more heat was needed can be easily adapted to block some unwanted sunshine. This can allow gardeners to extend the season for cool weather crops by a month or more.
So, whether the weather is getting too cold or too hot, there are simple techniques to let you grow food for more of the year.
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