Market Finds: Winter greens grown in ‘tunnels’

by Marlene Berlin

While shopping recently at the New Morning Farm market at Sheridan School, I overheard them describe growing greens in a “tunnel.” My vision of an underground bunker with lights was soon dispelled in my telephone conversation with Jim Crawford, who for more than 40 years has owned and operated this certified-organic farm in south-central Pennsylvania.

An older term for this method is “cold frame” farming, he explained. It acts like a greenhouse, but uses plastic sheeting instead of glass over a metal frame. During the day, the sun heats up the air and then the soil inside. The soil stays warm once the sun goes down. According to Jim, it can be 70 to 80 degrees Fahrenheit inside during the day while it is 20 to 30 degrees outside. And at night, the outdoor temps can fall to zero, but the soil temperature remains above freezing.

The tunnel method became popular about 30 years ago, when a do-it-yourself kit became available to farmers at a reasonable price. In 1991, Jim ordered two kits and constructed two 100 by 21 foot tunnels – large enough for a tractor to enter, plow furrows and spread fertilizer and composts. Four years later, a storm destroyed them. In 1997, he built two replacements in a more sheltered location. In 2012, he put up a third, larger tunnel – 180 by 30 feet – and in 2016 he built a fourth. The larger ones cost $26,000.

The tunnels provide an excellent environment for growing a variety of greens such as kale, collard greens, spinach, arugula and herbs. They even grow kohlrabi, which is in the broccoli family but does not require as much space. Space is at a premium, and greens and herbs like parsley, dill, cilantro and rosemary are compact growers. All are started in New Morning Farm’s 50 by 100 foot greenhouse, and they are transplanted into the tunnel in October.

Cabbage is hardy enough to stay in the fields through freezes. It is harvested in November and put into cold storage along with root vegetables such as potatoes, radishes, beets, and celeriac. New Morning Farm uses two stationary refrigerated truck trailers, 53 feet long and 8 feet wide, that maintain a temperature of between 33 and 36 degrees with high humidity. These root vegetables will supply the market through March.

From December through March, Jim and his helpers are at Sheridan School (36th and Alton Streets) on Saturday mornings during their winter hours: 9 a.m. to 1 p.m. They will continue to have eggs, bread, other baked goods, cheeses and delicious homemade applesauce. Many of these products and other canned goods come from neighboring farms and orchards. The organic citrus fruit they sell during the winter comes from Florida and is one of the few exceptions to New Morning Farm’s locally-grown rule.