Before I get into my thoughts on cool season crops, I wanted to mention a new book. It is the sixth edition of “Knott’s Handbook for Vegetable Growers,” updated and improved on by my friends and colleagues, Drs. George Hochmuth, University of Florida, and Rebecca Sideman, University of New Hampshire. I believe it is a must have for serious vegetable growers, Extension workers, researchers, teachers and other associated with the vegetable industry.
The first edition was written in 1956 by Dr. James Knott, who was then employed at UC-Davis. It was a compact compendium of factual data for commercial vegetable growers, with most of the data presented in tables and charts. It was filled with information on topics like transplant production, planting rates and spacing, methods for controlling diseases, insect pest identification and a multi-language vegetable dictionary. The sixth edition is available through a number of retail outlets.
Now, cool season crops: When I think of the wide variety of vegetables we can grow and market, my first thought is how we classify or sort vegetable crops. We classify them whether they are annual or perennial (asparagus vs. summer squash), warm season or cool season (tomatoes vs. kale) or fruit or vegetable (botanically, they are classified depending on which part of the plant they come from).
A fruit such as the tomato develops from the flower of a plant, while those developing from the other parts of the plant, such as roots, stems and leaves, are categorized as vegetables. Fruits also contain seeds, while vegetables are mostly direct seeded or transplanted crops.
I like to think that cool season crops are the first and last ones that a vegetable grower will plant and the first and last ones to supply some needed cash flow to a grower’s bank account, especially if you have a high tunnel to extend the growing season. Depending on one’s location, production of cool season crops in high tunnels can continue throughout winter.
It’s important for a grower to know the approximate last frost date in spring, and the first frost date in late summer/early autumn, where they are farming to determine planting and harvesting dates.
Cool season vegetables include artichoke, asparagus, beet, bok choi, broccoli, Brussels sprouts, cabbage, carrot, cauliflower, celeriac, celery, chard, cress, daikon, endive, escarole, fava bean, garlic, horseradish, kale, kohlrabi, leek, lettuce, mustard, onion, parsnips, pea (English, snow and snap), radicchio, radish, rhubarb, rutabaga, scallions, shallot, spinach, Swiss chard, turnip and watercress.
Many of these are what I like to term my “survival” vegetable crops – the ones that got the early settlers through the winter months until they could plant again in spring. In many cases they were root crops used in hearty stews. Today you could even market some of them as “survival” vegetables, such as turnips, parsnips, rutabaga, onions and potatoes. These are vegetables that can generally be stored in one’s root cellar for later use.
The neat thing about these early/cool season vegetables is that they cannot only withstand colder temperatures but, in many cases, they need these conditions to germinate, grow, set fruit and mature. Many growers have told me that their most winter-hardy vegetables, such as kale, collards or Brussels sprouts, even benefit from a light frost, as it converts the starches into sugars and improves the taste.
From a grower’s perspective I would recommend planting cool season crops early enough in spring so they can complete their growth cycle and be harvested before the temperatures get too warm. While it’s true that some cool season vegetables, especially some of the newer varieties, can withstand hot weather and will still grow, generally their quality becomes inferior. I always talk about is radishes that turn fibrous and unpleasantly sharp and pungent in hot weather and how broccoli can move to yellow flowers quickly and leave you with what I like to call “an organic bridal bouquet.” (If you can market that bridal bouquet, you deserve an award.)
The beauty is that many cool season crops can be sown in early spring and again in autumn, but it’s important to remember that they must be planted early enough to reach maturity before the onset of really cold weather that will kill many of them (except for your winter-hardy vegetables). Say you can grow a cool season crop of broccoli, then a quick warm season crop and then fall back to a cool season crop again. You have taken an acre of physical land and grown the equivalent of three acres of produce.
Many cool season vegetables are grown directly from seed, either as soon as the soil can be worked in spring or until the soil and air have reached certain minimum temperatures. To warm the soil faster in spring, you can cover it with black plastic, which may allow you to plant crops a bit earlier than what your calendar indicates, provided the air temperature is warm enough. There are other so-called season extenders like high tunnels and row covers that can advance your production schedule forward.
Some cool season crops such as leafy vegetables like salad greens and spinach can rapidly produce flowers and seeds is a process called bolting, which is a type of survival strategy to make sure the next generation of plants is present before the plant succumbs to temperatures that are too warm. Growers can choose bolt-resistant varieties, which are indicated in the commercial vegetable guides or from information gathered from vegetable trials or seed reps. I have also observed that cool season crops generally have shallower root systems than warm season crops, which means that these crops may need to be watered and fertilized more often. The plants have limited access to water because the root zone is small.
Throughout my career I liked to use plastic mulch, drip irrigation, fertigation, transplants, row covers and high tunnels to grow both warm season and cool season vegetables from asparagus to zucchini and to really increase the amount of production of a given parcel of land. Let’s use four-foot-wide black plastic mulch with the edges buried, resulting in a 30-inch-wide raised bed with a drip tape buried under the center of the bed. Start some broccoli transplants in the greenhouse and have them ready to plant as early as possible on your plastic bed in a double row about 18 inches apart and with 10 – 12 inches in the row. Grow that crop and harvest them, then mow down the broccoli, plant a crop of cucumbers in a single row, harvest them, and then come back with an autumn crop again, which could be broccoli or cauliflower. An excellent publication that explains all this can be found on this website.
Cool season crops can help you survive if times get tough, starting the cash flowing earlier in the season and running later in autumn – and even the winter months, depending on location and the technology deployed.
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