Gilmour’s planting zone map is a good resource if you are planning on planting winter vegetables, but it takes some consideration and thought, as well as know how and we’re providing the former here
Crucifers: These plants, which are sometimes referred to as brassicas or cole crops, are great for a winter garden. Some examples of plants in this category include mustard greens, turnips, brussels sprouts, kale, broccoli, cabbage, cauliflower, rutabagas, bok choy, and kohlrabi.
While many of these plants are quite hardy, others are more susceptible to cold weather. For instance, Chinese cabbage, bok choy, and cauliflower can easily be damaged by heavy frost. While you can still include them in your winter garden, you will need to cover them if the temperatures drop lower than about 28°. Bok choy should typically be harvested within about a month to a month-and-a-half of planting. If you enjoy mild weather during the winter in your region, you can include cauliflower in your garden.
Other crucifers are much hardier. Plants like cabbage, broccoli, kale, turnips, radishes, mustard greens, brussels sprouts and kohlrabi are capable of withstanding cold temperatures. They do best in areas that get a lot of sun during the day, even if the ground freezes at night. If the temperatures in your area are low enough that the ground is frozen around-the-clock, you will need to find a way to warm up the soil for these plants to thrive.
The total time to maturity can vary quite a bit, depending on the plant. Rutabagas require as long as 100 days, while French radishes are ready in as little as 29 days. Different varieties of the same type of plant also mature at different rates.
Root vegetables: These vegetables fall into a lot of different categories. Some are brassicas, which were mentioned earlier. Others include parsnips, beets, and carrots. Root vegetables like these do exceptionally well when the ground is frozen. In fact, many people recommend leaving them in the ground over the winter as a way of storing them. Plants like these do have certain requirements, however. They need plenty of sun, enough water, and ground that is not frozen. When temperatures get extremely cold, cover the plants with glass or plastic to warm up the soil. Avoid overwatering, as well.
Spinach: Spinach does exceptionally well in cool to cold weather conditions. When you cut it, it will grow back, meaning that you can continue to harvest it over a period of months. When the weather starts to warm up, however, it tends to bolt. Spinach can easily withstand frost, making it a great winter crop. To help the seeds germinate after planting, cover your garden with glass or plastic. Once germination occurs, take the glass away so that the small plants have a chance to adjust to the cold temperatures. Avoid planting New Zealand spinach. It lacks the hardiness of other types of spinach and will easily succumb to frost or freezing temperatures.
Alliums: Garlic, leeks, onions, and shallots fall into the allium category. If you put garlic in the ground in the fall and cover it with mulch, it will be ready to harvest by the middle of the summer. Leeks also do especially well over the winter. This includes the Giant Musselburgh variety. Shallots and onions generally do best in mild weather. You can, however, grow them when it is cold outside. Just be prepared to wait longer for them to mature. Immature alliums can be left where they are over the winter if they are ready to harvest before it snows. You can continue harvesting them even after snow is on the ground. As long as temperatures stay relatively mild, the plants will do quite well.
Lettuce: Lettuce grows best in soil that is not frozen. Some varieties tolerate cold temperatures better than others. For instance, wild lettuce does well when it is cold out while radicchio tends to do quite poorly. You can put lettuce in the ground as soon as the soil thaws. If you don’t see signs of germination in a week, try covering the ground with glass to warm it.
Swiss Chard: A cool-weather crop like swiss chard grows in a wide range of temperatures. Whether it is 20°F or 100°F, it will thrive. It also does well in many different types of soil. Even if temperatures drop down as low as 0°, it will usually survive, waiting for the weather to warm back up again. It is a great plant to have on hand since it can survive conditions that would kill other plants.
Herbs: As a general rule of thumb, herbs do well in cold temperatures. Basil is the only exception. It is extremely sensitive and will easily die if it gets cold. Other herbs, however, are some of the first plants to pop up out of the ground when spring rolls around. Mint, oregano, sage, and parsley are particularly good choices for winter. While dormant during cold temperatures, they come back early in the spring. Many types of rosemary do quite well. Any sensitive varieties can be planted in containers and brought inside when temperatures fall.
Cover Crops: When it comes to winter gardening, cover crops are almost always a great choice. Even though they won’t give you food right away, they are extremely easy to care for over the winter. When spring arrives, you can till them into the ground to enhance the soil before planting your other vegetables. Greens like these can add much-needed organic material to the soil and can reduce the risk of erosion. Crops that require little maintenance include red clover. Cereal grains are also a good choice and can be used to provide food the following year.
Certain vegetables should never be planted during the winter. Plants you should avoid include sweet potatoes, melons, okra, corn, squash, cucumbers, tomatillos, peppers, potatoes, tomatoes, and eggplant. Even a light frost can kill these plants, which is why they should only be planted in the spring. The only exception is if there is a reliable heat source that can keep them warm all winter.
