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Easy-Build Cold Frame
On this page find an easy building project for making a useful cold frame for growing vegetable starts and hardening them prior to transplanting, including:
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- The many beneficial uses of cold frames in home vegetable gardens.
- How cold frames gather and retain heat to help plants survive cold weather and temperatures.
- Extending garden seasons with a cold frame.
- A step-by-step demonstration of how to build a simple cold frame and install it in your garden.
Those living in cold climates give warmth-loving vegetables an early head start: Plant them in a simple cold frame you can build, heated by the sun and insulated by being buried deeply into the soil.
Use decomposition heat to help protect vegetables and produce growing inside the cold frame. Bury green manure deep below and around the sides of the box. This manure radiates heat for months as it decays, raising the temperature within the cold frame to 78°F (26°C) even when it’s well below freezing outdoors.
With the use of a cold frame, you’ll plant seed 6–8 weeks earlier in the season than would be possible for in-soil plantings.
Step-By-Step Instructions
Make your cold frame of waterproof ACX plywood and a corrugated fiberglass panel, fastening it with galvanized hinges, screws, and washers.
Gather the materials listed, and follow these steps:
Materials, Fasteners, and Hardware
Raw Materials:
1 – 4 x 8-ft. (1.2 x 2.4-m) 3/4-in. (19-mm) ACX plywood panel
1 – 26 x 36-in. (66 x 90-cm) corrugated fiberglass panel
1 – 96 x 2 x 2-in. (244 x 3.8 x 3.8-cm) dimensioned lumber
Cut Components:
Careful cuts of a single sheet of ACX exterior plywood will provide all the dimensioned exterior wood components listed below that are needed to construct the cold frame.
1 – 26 x 36-in. (66 x 90-cm) back panel
1 – 22 x 36-in. (56 x 90-cm) front panel
2 – 22 x 26 x 28-1/2-in. (56 x 66 x 72.4-cm) side panels
2 – 5-1/2 x 30-in. (14 x 76-cm) vertical cover frames
2 – 4 x 36-in. (10 x 90-cm) horizontal cover frames
2 – 26 x 2 x 2-in. (66 x 3.8 x 3.8-cm) back corner braces
2 – 22 x 2 x 2-in. (56 x 3.8 x 3.8-cm) front corner braces
Hardware:
36 – 1/4 x 1-1/4-in. (6 x 32-mm) Phillips galvanized wood screws
24 – 1/8 x 5/8-in. (3 x 16-mm) Phillips galvanized wood screws
12 – 1/2 x 1/8-in. (12 x 3-mm) galvanized washers
2 – 2-in. (50-mm) galvanized butt hinges and mounting hardware
How to Build a Cold Frame
Cut component pieces from plywood, then assemble the box by fastening the side, front, and back panels to the front and back corner braces with wood screws.
Cut 3/4-in. (19-mm) kerfs into one side of each of the cover’s two horizontal frame members. Center and attach the fiberglass panel to the cover’s horizontal frame members with wood screws and washers.
Fit the fiberglass panel into the kerfs of the vertical frame members [See: Detail of assembly illustration and photograph, below).
After the fiberglass panel’s edges are in the kerfs of the cover’s vertical frame members, complete assembly of the cold frame’s cover by joining and fastening the cover’s four frame members.
Overlap the horizontal and vertical cover frame pieces at their corners, and fasten them together at each corner with 3 wood screws.
Last, secure the fiberglass panel in the kerfs of the cover’s two vertical frame members with wood screws and washers. [See: Detail of assembly illustration below].
Fit the 2 butt hinges 1 ft. (30 cm) from each corner of the back panel, fastening them with supplied hardware. Fasten them to the underside of the cold frame cover.
In a sunny, protected spot, dig a rectangular hole 36 x 42 x 24 in. (90 x107 x 60 cm) deep. Line it with plastic, fitting the cold frame into the hole. Backfill around the cold frame with soil.