Many gardeners enjoy gardening in cooler weather because there is less weed pressure, the temperatures are more enjoyable, they enjoy the types of crops you can grow in cool weather and like everything you grow in your garden, the food will be tastier and higher in vitamins than their supermarket alternatives.
Winter gardening is about eating food fresh from your garden during the winter, not about growing the food in the winter. Due to the shorter days and much cooler air and soil temps, crops don’t grow much in the winter, they grow in the fall. To have a successful winter garden, you should aim to grow enough cold hardy plants in the fall that you can leave in the ground and harvest all winter. Think of your garden as a large refrigerator that you don't have to pay for!
In cooler weather you can generally grow leafy crops (you eat the leaves) and root crops (you eat the roots). Some, like beets and turnips, are great because you can eat the root AND the leaves.
Plant cold hardy or frost hardy varieties. Of the cool weather crops some are more cold hardy (their cold tolerance level) than others. If your goal is winter harvesting be sure to select cold hardy plants and cold hardy varieties of plants. Here is a quick list of cold hardy plants that I have seen live through frost, freezes, and even snow on the ground:
Mulching with a carbon source helps protect your soil and keeps it from freezing for a while. Think of it as a blanket for your plants (but don’t cover them!). Mulching also helps retain moisture, suppress weed growth, and when its time to turn your soil, you are folding in nutrients and organic matter. Here are some good sources of mulch: Leaves (free and plentiful in the fall, become a leaf thief and take bags from neighbors as well), straw (preferred over hay because it has less weed seeds in it), hay (the top cutting of grass, therefore it has seeds in it that may sprout in the spring), partially decomposed compost, Shredded paper
These tools will help you adjust the temperatures of your crops which will keep you crops alive longer in cold weather and may keep some crops growing past when they would normally go dormant.
These are simply wooden planter boxes with glass lids that you can open to vent. During the day keep them vented. At night close the lid. Cold frames can be used as mini greenhouses as you start plants or they can house plants for the life of the plant. Many gardeners have success growing lettuce in cold frames throughout the winter.
Thin fabric or plastic that is gently wrapped over the plants like a blanket. Some plants do fine with the row cover resting right on the plant, other more delicate plants prefer that the row cover is held up by thin metal tubing or PVC pipe. Row covers don’t prevent the temperatures from getting just as cold as outside the row cover. What they do is simply slow down the rate of the temperature decrease. Often, it is not cold temps that damage plants, rather it is the rapid drop in temperatures that often happens in the winter when the sun goes down.
A greenhouse is a small room with glass or plastic sides and roof that let light in. They let the sunlight in and hold heat well which will help keep your winter plants alive and possibly growing in the winter. Some greenhouses have heaters which allow gardeners to grow almost any crops they want as long as they are careful about regulating the temperature. Greenhouses are also commonly used to start plants in the early Spring before transplanting them in the ground.
Some plants like spinach will grow enough to get established in the fall, then go dormant in the winter (you can still harvest if you want), and then in the Spring they start growing again. Because these plants that got established in the Fall already had a healthy root system, they really take off when it starts to warm up. In this way, you can have VERY early spinach.
Consider setting aside part of your winter gardening for growing a cover crop (also called green manure) that will protect your soil and build fertility for next spring and summer. Cover crop seeds are spread over a bed in the fall, grow all winter, and then are dug under in early spring. Here are a couple good winter cover crops: Crimson Clover, Winter Rye, Hairy Vetch
Another way to build your fertility for the next year is to sheet compost over the late fall and winter. Sheet composting also called lasagna composting is essentially building a very low spread out compost pile in your garden that will break down and feed your soil. To get started, spread food scraps or other nitrogen (coffee grounds, farm animal poop, etc) in your garden area. Then, add a thick layer of leaves (plentiful in the fall) and give it a good soaking with water. If you want, add another layer of food scraps, leaves, and water on top. Then, leave the spot alone until the spring when your can till or dig all those good composted nutrients into your soil.
Use the down time to take care of your tools and plan your spring and summer gardens. Another way to keep the gardening hobby going in the winter is to use the natural rhythm to do some gardening related work that doesn’t involve digging in the dirt. All tools need cleaning, sharpening, and other maintenance. Why not get this done while it is cold out so that you will be ready for spring? You could also use the winter months to read seed catalogs, plan your garden, and dream about spring. That way, when spring does come, you will be ready and itching to get out and work the soil.
By Henry Owen with assistance from Kathy Metzo and Carol Adams