Planting the vegetable garden is not just a warm-weather job. While top crops such as tomatoes and peppers can't tolerate freezing temperatures, many other vegetables grow in and even prefer cool weather.
The main trait that sets cool-weather crops apart from their warm-weather counterparts is the ability to survive frost. While cabbage and onions slough off a freezing night in the 20s, that would kill an eggplant or cucumber. In warm climates gardeners can plant a fair share of the vegetable garden in winter for a spring harvest, while gardeners in the North and Midwest can plant some crops only as early as March for an early-summer harvest.
The trick is to know which crops are which and when's the best time to plant cool-weather fare. Wait too long and crops such as lettuce, spinach, and radishes quickly turn bitter in the too-hot temperatures. That may be especially true if the unusually warm early-spring weather continues in much of the country. Don’t rush frost-sensitive crops, though, because a sudden return to seasonal norms is possible before all danger of frost is gone.
For the lion's share of the United States in USDA Hardiness Zones 5 and 6 (winter lows that average zero to minus 20 degrees), cool-season crops are best planted from mid-March through mid-April. In colder areas of Zones 3 and 4 or even colder, push planting back 2 to 4 weeks or more later. In warmer Zones 7 and 8, plant 2 or more weeks earlier. In the hottest regions, some crops can be grown all winter.
The entire crop of cool-season plants doesn’t have to be planted all at once. To extend the harvest, stagger the plantings at 1- or 2-week intervals.
Here’s a look at some of the most common and easiest-to-grow cool-season veggies:
Broccoli, cabbage. Both of these do well when young plants are set out 6 weeks before the last frost date. Depending on variety, they'll be ready to harvest in two to three months. A fall crop can be planted in late summer.
Cauliflower is treated similarly to broccoli and cabbage. Cauliflower is slightly more cold-sensitive and planting may be delayed until about 4 weeks before the last frost.
Onions, leeks. Among the most cold-tolerant of all crops, these can be started as seed or plants (or baby "sets" in the case of onions) 8 weeks ahead of the last frost. Onions are harvested after the foliage flops over and browns; leeks can be harvested throughout summer.
Peas. Also extremely tolerant of cold, peas should be direct-seeded into the garden in late winter or as soon as the soil is workable. Traditionally many gardeners plant them on St. Patrick’s Day. Pods can be harvested until heat stops flower production.
Potatoes. Cut potato pieces with an "eye" (dormant sprout) can be planted about 4 weeks ahead of the last frost and harvested in mid-summer after the foliage dies back.
Lettuce, spinach, mustard, kale, greens. Most leafy greens are frost-tolerant and actually taste mildest when they mature in cool temperatures. Sow seeds from late winter through early spring, and harvest leaves continuously until high temperatures cause them to turn bitter. Then sow more heat-tolerant types of lettuces, or greens such as collards and chard. Plant cool varieties again in fall.
Carrots, turnips. Seed directly into the garden about 4 weeks before the last frost and harvest when the shoulders (top part of the root) are of a mature size – or before. Don’t wait too long or the roots will turn woody. Plant a second crop in early fall for winter harvest.
Radishes. One of the fastest-maturing crops, radishes are quick to turn spicy when the weather gets hot and dry. Sow seed 6 weeks before the last frost and harvest about 30 days later. Sow again in fall after night temperatures cool.
Beets. Direct-seed these into the garden about 4 weeks before the last frost, for a spring crop for early-summer harvest However they'e also heat-tolerant enough to grow in summer as well, so keep seeding every few weeks for season-long beets.