What are cold frames?

How Cold Frames Work

The function of a cold frame is to utilize passive solar energy similarly to a greenhouse, trapping heat inside the space and allowing UV light to your plants. In a greenhouse it is beneficial to add materials such as gravel, bark, large rocks, jugs of water... to increase the thermal mass. Every evening the stored heat dissipates and rises to the top 2-3 feet of the structure. Because a greenhouse is a large space to heat, fans are sometimes used to circulate the warm air that rises to the top bringing it back down to where the plants are.

Cold Frame vs Greenhouse

   In a cold frame the thermal mass is the soil the plants are growing in. Building a frame lower to the ground holds the warm air down low next to the plants as it dissipates from the soil throughout the night. Because a cold frame is so efficient at trapping heat, it is important to know when to vent. For example, on a 45*F day, with good sun exposure, an unvented cold frame can reach temperatures as high as 90*-100*F effectively cooking your plants. A vented cold frame will allow the excess heat to escape and maintain a comfortable temperature throughout the day. Before the sun sets and the evening shadows cool the night, closing the lid will maintain a warmer ambient air temperature inside the cold frame. If temperatures are not getting above 40*F leave the cold frame closed. In our cold frame, we have monitored soil temperature up to 20*F warmer than outside soil temperatures. This makes a great place to start seeds in the spring or extend the growing season in the fall.

Automatic Venting Cold Frame

  If you have used a cold frame or a greenhouse, you have probably overheated a few plants from forgetting to vent. The automatic venting system we have added to our cold frames has practically eliminated the possibility of overheating the plants. The automatic vent system opens through the back panel, which is independent of the manual venting system through the lid, The lid has 6 locking vent adjustments. The cold frame can always be accessed through the lid for watering, harvesting, and tending. For those of us with busy lives that can’t check on our garden every day, this feature is a plant saver.

Cold Frame with Automatic Vent Opener

Materials Matter

  By combining the rot/pest resistant properties of western red cedar with the durability and transparency of the corrugated polycarbonate and using galvanized/stainless fasteners, these cold frames are built to withstand and last through the seasonal elements. Whether you are starting seeds, hardening off seedlings, growing a spring/fall/winter crop, wintering over perennials, or simply protecting your sensitive plants, our cold frame is "The Tool for Gardeners".