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In the spring of 2020, when dozens of people started vegetable gardens, a local farmer selling tomato plants through the honor system (yes, those still exist in the rural area where I live) had a large handwritten sign which said in all caps: “Do not plant tomatoes before the last spring frost!” I hope his customers took this advice, otherwise instead of juicy beefsteak tomatoes in August, they would have dead plants in May.
There is no single date for planting tomatoes or other warm season vegetables. The USDA hardiness zone map covers a wide range of temperature zones, and the dates of the last spring frosts and first fall frosts vary widely – in New Orleans it’s Feb. December 19, and in Billings, Montana, it’s May 15 and Sept 26.
Instead, to plant your vegetables at the right time, it’s essential to know the difference between warm-season and cool-season vegetables.
Tomatoes are warm season vegetables, as are other members of the nightshade family like eggplants and peppers, as well as beans, corn, cucumbers, eggplants, melons, watermelons, zucchini and summer squash, pumpkins and winter squash, sweet potatoes and herbs. like basil and cilantro. These crops are very sensitive to cold. A temperature below 32 degrees Fahrenheit (0 degrees Celsius) kills the entire plant immediately. Temperatures in the mid-50s and below stunt the plant’s growth, so it will not produce fruit (or only stunted fruit).
To grow properly, warm season crops need warm air and warm soil. Crops that are sown directly into the ground, such as beans, do not germinate well when the soil temperature is even below 60 degrees Fahrenheit (15 degrees Celsius).
Due to their temperature requirements, in most climates, warm season vegetables have only one growth cycle – from late spring to late summer – and one harvest. The warm and sometimes even hot days of fall might trick you into thinking you can grow warm season vegetables well into the fall. Sure, you can protect your tomato plants on nights when frost is expected, but that’s cumbersome and doesn’t work for all crops. Even without frost, nighttime temperatures in early fall are already too cold for cucumber plants, for example, which could turn bitter.
In cooler climates, the relatively short growing season, which is calculated as the number of days between the last spring frost and the first fall frost, makes it necessary to start warm season crops from seed in indoors, or buying young plants from a nursery that started them in a greenhouse. Watermelons, for example, take 90 days from seed to harvest, so you need to get a head start on the growing season to adapt them to the warm weather window.
Fresh season vegetables
At the other end of the spectrum are cool-season vegetables: asparagus, beets, broccoli, Brussels sprouts, all cabbage, carrots, cauliflower, Swiss chard, kale, leeks, lettuce, onions, parsnips, peas , radishes, spinach, rutabagas and turnips.
They can be planted in early spring or fall, unlike warm season crops they have two growing seasons.. But just like warm-season crops, they must fall within a specific time window. Warm season vegetables should be sown or planted early enough in the spring to reach harvest before temperatures get too hot. Hot weather doesn’t necessarily kill them, but they do become nasty. Take radishes, for example, which become fibrous and develop a super pungent, unpleasant taste. Leafy vegetables like salad greens grow in hot weather – they send up tall stalks of seeds, which is nature’s ingenious trick to ensure there’s a next generation before the summer heat kills them. plants.
Cool-season vegetables not only tolerate cold temperatures, but they need them to germinate, grow, fruit and ripen. Spinach needs a soil temperature between 45 and 68 degrees Fahrenheit (and 7 and 20 degrees Celsius) to germinate. If you live in USDA zones 9 through 11, you may be able to grow them in the winter. Any area above this is simply too hot for cool-season vegetables.
Some of the cold season vegetables are even winter hardy. They stop growing when temperatures stay consistently below zero, but they can still be harvested and root vegetables can be dug up until the ground freezes..
I’ve always escaped why kale is grown in the summer in the United States (in my native Germany it’s a winter-only vegetable) because, like other crucifers like rutabagas and Brussels sprouts taste even better after the first frost because the cold converts the starches to sugar. I harvested kale and collard greens when they were covered in half a foot of snow.
Some cool season crops are easier to grow than others. The leafy types are generally easy, those that form dense buds are trickier. Brussels sprouts have a reputation for being difficult to grow and I can attest to that; I tried Brussels sprouts for several years in a row and gave up growing them. Likewise, I gave up growing artichokes, a warm season crop, because the growing season here in Pennsylvania is too short.
Good reasons to grow cool-season vegetables
Growing cool season vegetables can be easier than growing warm season vegetables. They need less frequent watering because it usually rains more in the fall and the soil dries out less quickly because it’s cooler. Plus, weed growth slows in the fall, so it’s less of a challenge to keep your flower beds weed-free. There are also fewer insect pests, as many have already completed their annual life cycle. Fall is the only time I can plant arugula without it being devoured by flea beetles.
If you want to grow cool-season vegetables, planning is needed now. Make a map (to scale) of your garden plot and note what you plan to plant and where to ensure you have space for cool season vegetables when you need them. In late summer, when I usually plant kale, many of the warm season vegetables are still in full swing, but I have empty space because the peas I planted in the spring are long gone. Always keep in mind that crop rotation – not planting crops of the same family in the same location for at least two consecutive years – is essential for plant health.