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cold framed

April 19, 2011

there comes a time in a seedling’s life when it must leave the warm comfort of the greenhouse and venture out to the fields to take root, grow, and produce.

since the conditions outside can be so different from inside the greenhouse (temperature fluctuations! wind! rain!), plants tend to fare better when they have a chance to transition before enduring the abuses of the great outdoors full time. this transition is called “hardening off.” there are several ways to harden off plants — if you just have a few flats, simply bringing them outside for a few hours a day, several days before transplanting does the trick. with dozens of trays ready at once, that method isn’t practical for us, so we let the plants get accustomed to the elements in a small hoop house which, because of its function rather than its form, is referred to as a cold frame.

a cold frame is essentially a small enclosure that lets in light, traps in solar heat, protects from wind, rain and snow, and can be opened to moderate temperature and exposure to the elements. the most simple design is a box with a clear glass or plexi cover that sits directly on a garden bed. in chicago, i taught workshops on how to build these in community gardens, enabling gardeners to start plants earlier in the spring and keep them alive later in the fall (or in some cases, through the winter). we used a design from eliot coleman, the guru of winter harvest for small farmers and market gardeners. last month i visited the ruby garden in rogers park — a garden which i helped to plan and create in 2009 — and many of those cold frames we built were in use, like the one on the right.

back at the farm, our cold frame isn’t a box style — we decided to go with a tunnel made of pvc hoops covered with clear plastic. also, since our seedlings are already in containers, the cold frame has a floor of weed-cloth and the plants sit on pallets to ensure good drainage.

the construction is simple: pound lengths of rebar into the ground every few feet. slip one end of each 20′ pvc pipe over the rebar, then bend and slip the other end on. tie the hoops together to keep them upright and stake each end of the rope. cover with plastic, and anchor it with sandbags and bungee cords. voila!

we put the plastic on and the plants inside, keep it tightly covered at night to protect from freezing, and (unless it’s pouring rain) open it up to get the plants used to the cold and wind and sunshine during the day.

after a few days (or up to a couple weeks), the plants are ready to transplant out in the field. we did our first transplanting on wednesday and thursday — broccoli, cauliflower, kale, pac choi, chinese cabbage, kohlrabi, chard, lettuce and beets!

and then came a long series of storms, bringing 40 mph+ wind, rain, snow, sleet, hail, rain, snow, more rain, more wind…

our sandbags and bungee cords just weren’t a match for that:

we’ve now removed the plastic and got the hoops upright again, but we’re waiting for this series of storms to pass before reassembling. in the mean time, all the plants that aren’t already in the ground are back in the greenhouse, filling every available surface and waiting for us to create a new incarnation of their halfway house.

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