Cold Frames as Season Extenders
David Bearg, Sage Farm, Concord, MA
One aspect of growing more of your own food is by extending the growing season. One approach for extending the growing season is to utilize cold frame growing structures. These structures go very well on top of irrigated raised bed growing areas. Figure 1 illustrates such a growing chamber all closed up and using double wall polycarbonate glazing.
Figure 1: Closed up Cold Frame with Double-wall Polycarbonate
In the background of Figure 1 a second cold frame has its glazing elevated into the venting position. As shown in Figure 2, the glazing could also be greenhouse plastic secured over a wooden frame. The position of the glazing panel in the venting mode is designed to allow generous natural ventilation, as the warm air in the cold frame can easily escape at the upper end, while then creating the suction to draw cooler outdoor air in at the lower end, and then across the growing bed. To facilitate moving the glazing from the closed to the venting position and back again, a pivot arm, cylinder and hole mechanisms is used. A close-up of this detail is shown in Figure 3. Not only does this mechanism make it easy to go between the closed and venting configurations, it also allows the glazing to be completely removed.
Wooden frames also come in very handy as well to provide something to attach chicken wire to, as shown in Figure 4. This has been found to greatly reduce predation of the vegetables by the woodchucks, deer and chipmunks that would otherwise do a lot of damage during the warmer part of the growing season.
Figure 2: Greenhouse plastic on wooden frame, in venting mode.
Figure 3. Detail of cylinder and hole mechanism
Figure 4. Chicken wire and wooden frames
Being able to completely remove the glazing allows the growing area to be open to the rain. Access is also granted for transplanting, weeding and harvesting. Propping the glazing panel up at the north end of the cold frame can also reflect more sunlight to the growing area (see Figure 5).
Figure 5. Glazing Panels to reflect more sunlight
Aluminized Mylar (see Figure 6) can also be used for this purpose.
Figure 6. Aluminized Mylar along rear wall
The bottom line is that cold frame structures can be used to extend the growing season. All of these photos, including Figure 7 that demonstrates that lettuce can survive a killing frost, were taken on October 15, 2012.
Figure 7. Lettuce on October 15, 2012