Broccoli, cabbage and cauliflower. I direct-seed these vegetables in the warm garden soil in mid-August. It is important to choose specific varieties intended for over-wintering. Springtime is the best over-wintering cabbage I've found, while several varieties of broccoli and cauliflower over-winter well. Germination is usually successful, so long as the soil is kept evenly moist during those hot August days. Reemay is very helpful. Instead of sowing in rows and wasting a lot of transplants when thinning, I sow five or six seeds in the final spots I want the plants, and space these spots 18 inches apart in all directions. When the plants are 3 inches tall, I thin each spot to three plants. I do not fertilize at all in the summer and fall if the soil is still moderately fertile from previous fertilizer applications, since I want small hardy plants to survive the winter. In early March when spring growth begins, I thin the spots to two plants each and fertilize them heavily. Early April I fertilize again. I leave two plants in each spot to have a backup. Depending on the weather, some plants may produce in March, but the main crop comes in April and May.
Spinach, lettuce and other hardy greens. I sow these vegetables in early to mid-August for harvest beginning in late October, and again in mid-September for over-wintering and harvest the next April. Their growth really slows down toward the end of September because of less daylight, even if the temperature stays warm, so it is important to get the vegetables intended for fall harvest sown by mid-August. Over-wintered lettuce and spinach can give harvest for up to two months in the spring before bolting, which is very rewarding at a time when there is not much else fresh available from the garden.
Root crops. Parsnips sown in spring or summer over-winter well in the garden and can be dug as needed through the winter until the end of April, when they start sending out new growth and depleting the roots of nutrients. Rutabagas sown in July can be kept in the ground until needed. Potatoes should not be over-wintered in the ground because of disease problems. Carrots can be very difficult to over-winter in our area. Even though they are hardy, the carrot maggots tend to turn them into mush during the winter. I have given up on over-wintered carrots, after trying row covers, wired-covered cages etc. to shield out the adult carrot rust flies. Leeks sown in spring are also very winter-hardy and can be kept in the garden through next April.
Herbs. Parsley sown in spring or summer is very winter-hardy. Oregano survives so long as the temperature stays in the 20s, provided that there is no freezing rain. Even if it dies back, it will send out new growth in March. Chives die back in November, but start growing again in January. Rosemary survives down to the mid-20s. Thyme is extremely hardy.
Cloches and cold frames are very helpful in winter and early spring gardening. For instructions on how to build them, please contact Sally-Ann Sadler at the Seattle Food Garden Project. Mulching around the plants is helpful in preventing the ground from freezing. You can use leaves or straw. Grass clippings are not recommended, since they give off plenty of nitrogen, which fertilizes the plants and prevents them from becoming hardy.
Some seed companies have special winter gardening catalogs. I use almost exclusively seed from Territorial Seed Company in my winter garden.