Springtime Broccoli is Made in Winter
In Richmond County, the farmers’ market starts up in late April or early May, but local growers typically have little to sell at that time. A market window is thus available for crops that are ready to harvest at that time. For example, at the Sandhills AGInnovation Center Demo Farm we will be testing an overwintering, sprouting broccoli that can be planted in late summer or early fall to provide a 3-week harvest in early spring. This new variety needs protection only if the temperature drops below 20 degrees F. We will also see if customers will buy it, since it differs from standard heading varieties.
Other crops that can overwinter for early spring harvest can be divided into three groups. The “hardiest” (most cold-tolerant) group includes leeks, parsnips, and spinach. Spinach, in particular, can survive even at 12°F. The “hardy” group includes brassicas such as cabbage, broccoli, kale, and mustard. For example, we currently have brassica salad greens still growing in January in an open-ended high tunnel on the Demo Farm. The “semi-hardy” group includes beets, chard, carrots, cauliflower, lettuce, and peas. Even these latter crops can survive at 25oF or colder. Even if the cold damages the plants, they can usually recover in the spring.
Not just crop but also cultivar selection can contribute to season extension. The first cultivars planted of a particular spring-planted crop should be ones that can germinate better in cool soil. Likewise, the first cultivars planted of a fall crop should be ones that can tolerate warmer temperatures. For example, Green Magic broccoli could be followed by Emerald Star and then Marathon. Planting different cultivars with a range of maturity times can likewise extend the harvest season. For instance, 50-day “Provider” bush beans (which also tolerate cool soil) can be followed by 56-day “Affirmed” bush beans. Furthermore, instead of direct seeding, using transplants can give a 3- to 4-week head start on a summer crop. Transplants started in late winter will need to be started in a greenhouse or under a clear plastic cover. If the soil is too cold, the seedlings are more susceptible to disease. Transplants started in summer would need shade.
In fall, also, few produce items are for sale at the farmers’ market apart from sweet potatoes and collard greens. Two types of crops could fill this autumn niche: quick fall crops and season-extended summer crops. The quick fall crops could include lettuce, mustard greens, peas, radishes, and/or spinach. The season-extended summer crops could include cucumbers, flowers, melons, okra, peppers, squash, and tomatoes, grown with protection in the form of a high tunnel, caterpillar tunnel, low tunnel, or floating row cover. Medium-weight, spun-bonded row covers provide 2-4°F protection in the spring, and more than that in the fall when more heat is stored in the soil. High tunnels allow planting summer crops 3 weeks earlier and extend the season about 4 weeks into the fall.
Windbreaks and growing crops on south-facing slopes can also enable season extension. Windbreaks protect young plants from wind and sand-blasting damage. By protecting young plants, a windbreak improves early growth and leads to earlier harvest, especially with
cucumbers, melons, eggplant, tomatoes, peppers, okra, and squash. A windbreak can be as simple as a strip of rye between rows, planted perpendicular to the usual wind direction. To obtain adequate growth before the spring vegetable planting, rye should be planted in the fall.
In summary, careful cultivar and crop selection and season extension techniques (covers, site selection, and wind protection) provide many advantages. The farmer receives income over a longer period of time, and sells at higher prices in the extended season, along with higher yields and quality. He or she also has more ability to gain and retain customers, and to offer more consistent employment to workers. These benefits can outweigh the disadvantages of less time off in winter, more intensive management, higher production costs, and plastic disposal issues.
Nancy Power is the Commercial Horticulture Agent for the N.C. Cooperative Extension of Richmond County.