Cold Frames are great for stretching the garden’s growing season at both ends. In the spring cold frames provide a sheltered area for seed starting and to harden off transplants that were grown indoors.
During the fall, cold frames enable you to harvest fresh vegetables longer by protecting your plants from frost and cold temperatures.
Cold Frame Styles and Construction
Building a cold frame can be as simple as attaching a discarded window sash to a box shaped framework of wooden boards or by placing the window sash over a group of straw bales arranged to form a rectangular base.
Instead of constructing a homemade cold frame, you can purchase commercial units made out of high tech materials that are designed to retain warmth and transmit sunlight to the plants growing inside.
Inexpensive models are available that are constructed with a plastic or metal tube frame that’s covered by a transparent, woven plastic fabric. This style of cold frame is lightweight, portable, and an easily be moved from one section of the garden to another, making them ideal for use in raised bed gardens.
The more expensive types of cold frames use an aluminum framing that’s covered with twin walled poly-carbonate panels. These units are sturdier and provide better insulation, but are not as portable and usually remain in a permanent, fixed location outside of the garden.
Cold Frame Gardening During the Fall
For growing fall gardens, plants can be sown directly in the fixed location cold frame during late summer, or winter vegetables that were planted in the garden beds can be covered with one of the portable style cold frames.
In cold northern climates, even with the shelter of a cold frame, plant growth will slow or stop as temperatures drop below freezing. But the cold frame will enable you to continue growing and harvesting organic vegetables well beyond your normal growing season.
When spring returns, many of the vegetables that were planted in the cold frames the previous fall will resume growing to offer extra early fresh produce at a time that the garden’s beds are still frozen and inactive.
Using Cold Frames in the Spring
At the end of winter the cold frame can be used as a nursery bed for starting seedlings of lettuce, kale, spinach, and other leafy greens. Sow the seeds thickly and let them germinate and grow inside the cold frame until spring arrives. When outdoor conditions are suitable the seedlings can be thinned and transplanted from the cold frame into the garden’s raised beds.
Cold frames can also be used in the spring to harden off transplants which were started indoors and grown under lights. Placing the flats or containers of transplants inside the cold frame will allow them to gradually adjust to the harsher growing conditions encountered outdoors, without the need to bring the plants back inside during the night.
Crops growing inside cold frames can survive with little or no watering or other attention over the winter months. But you will need to keep a close eye on the plants growing in cold frames during the fall, and especially during the spring to ensure that they receive sufficient moisture and to vent the cold frame to prevent plants from overheating on warm days.
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