When to Plant Cool-Season Vegetables
Cool-season vegetables usually develop edible roots, stems, leaves, or buds, such as cabbage, onions, and potatoes. These crops grow best when soil temperatures range between 40°F and 75°F. Cool-season vegetables are unique in that their seeds germinate best in cool soil. They are usually planted as soon as the soil can be worked in spring. In most areas, that’s between 2-4 weeks before the last spring frost. Avoid planting in soggy soil that is still full of moisture from snow or spring rains. Wait until the soil dries out a little so your seeds or transplants don’t rot. Seed packages or plant tags will tell you the specific temperature at which a particular vegetable can be planted. A soil thermometer ($19, The Home Depot) can come in handy if you want to start your cool-season vegetables as soon as possible. Some example crops for various temperatures include:
At a soil temperature of 40°F, plant arugula, kale, lettuces, parsnips, peas, radicchio, radishes, and spinach. At a soil temperature of 50°F, plant Chinese cabbage, leeks, onions, Swiss chard, and turnips. At a soil temperature of 60°F, plant beets, broccoli, Brussels sprouts, cabbage, carrots, and cauliflower.
The root systems of cool-season plants are shallower and the plants themselves are smaller than warm-season vegetable plants. They typically stop producing in early summer when temperatures reach 80°F. In regions where nights remain cool, you can sow cool-season vegetables every two weeks for a continual harvest that extends into fall. This is called succession planting. In warmer regions, plant cool-season vegetables as early as possible in late winter or early spring, and plant seeds or transplants again when temperatures cool down in fall so you can enjoy winter harvests. A few cold-hardy vegetables, such as carrots, parsnips, and garlic, can survive throughout winter in some regions when insulated under a blanket of snow. Look for vegetables labeled “frost-hardy” to know which ones will tolerate prolonged freezing temperatures. Some varieties also have higher frost tolerance. For example, ‘Coronado Crown’ broccoli tolerates frost better than many other types.
The Best Time to Plant Warm-Season Vegetables
Warm-season vegetables, such as tomatoes, peppers, corn, and okra, originated in tropical climates. Technically, they grow edible fruits (the reproductive part of the plants where the seeds develop) instead of edible roots, stems, leaves, or buds, as cool-season crops do. These tender crops are killed by frost and won’t perform well if temperatures drop below 50°F. Don’t bother to plant before the soil and air temperatures have warmed up above this point in spring or early summer because the seeds and plants simply won’t grow. Wait until about two weeks after the average last frost date for your region to plant warm-season crops. You can encourage many warm-season crops to slowly continue growing into fall by protecting them from frost with row covers ($15, The Home Depot), cold frames, and other season-extending devices. Warm-season crops can be sown indoors from seeds. An early start inside gives them a jump on the growing season, but remember to harden off seedlings before transplanting them into the garden. This means to slowly acclimate them to outdoor life by placing them in shade instead of full sun, and allowing them to adjust in short periods to outdoor temperatures over a few days. These popular crops do best during the warmth of summer: artichoke, beans, corn, cucumber, eggplant, melons, okra, peanuts, peppers, squash, sweet potatoes, tomatillos, and tomatoes.
