Let There Be Light: How To Build A Gardening Cold Frame

gardening coldframe

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Fall is approaching, but that doesn’t have to mean an all-out-stop to your gardening. Building a cold frame for your garden allows you to grow seasonal plants and produce in inclement weather. Sunlight in, cold air out.  A cold frame consists of a bottomless box frame with a top made of glass and clear plastic that allows the sunlight in but protects plants within from cold air. With these easy instructions and tips, you can create your own cold frame to extend the life of your garden.

According to Bronx Green-Up, a cold frame can be built to any dimensions you desire. However, their guide recommends a wooden cold frame that is three feet wide and four feet deep — using untreated lumber if you’re planning to grow food. It also suggests reusing an old window for the top.

The Bronx Green-Up guide lists the following needed materials for building your own cold frame:

  • 1 2×8 board, 3 feet long
  • 1 2×12 board, 12 feet long
  • Saw
  • Drill and Drill bit
  • Box of 3½-inch outdoor screws
  • Plastic or glass or old window to be used for the top of the frame
  • 1 or 2 small door hinges (to join the top to the frame)
Working in the Cold Frame

‘Working in the Cold Frame’. Image courtesy of Susy Morris.

The first board on the list of materials will serve as the front wall. The 2×12 board will need to be cut to create three segments — a three-foot length for the back wall, and two four-foot sections to serve as the sides of the frame. Next cut the two side pieces so that the height measures eight inches on the front end and 12 inches on the back side.

Pre-drill holes in the corners, then join one corner at a time on a flat surface to ensure accuracy. Once the frame has been assembled, attached the top using the hinges to secure the window, glass or plastic top.

Bronx Green-Up’s guide suggests setting up your cold frame in an area that receives southern exposure, ensuring it will get the most sunlight. Depending on what you’re growing, the cold frame can be used to plant seeds earlier in the spring or later in the fall, then transport the seedlings into your garden in ideal weather. The plants become adapted to their environment better in a cold frame than if the seeds are started in an indoor garden.

When you’re planting in your cold frame is equally as important as what you’re planting.

  • Greens such as lettuce, arugula, parsley, radish, scallion, spinach and swiss chard, which will need to be harvested as baby greens.
  • Ensure that tender plants are packed kept in pots or pack it with soil, mulch and leaves to insulate it. Keep the soil moist, but do not overwater your plants in the cold frame or they could rot.
  • On warmer days, the cold frame should be ventilated.

Keeping a thermometer on the surface of the soil can help you determine when it’s time to vent your cold frame. Ideally, in the spring, the temperature inside the frame should be about 70 degrees F, while 65 degrees F is recommended for the fall months. If you’re unsure how much to vent, the Bronx Green-Up suggests erring on the side of venting too much, as it could allow the plants to build up a tolerance to the colder weather and grow hardier.

A cold frame can satisfy your green thumb’s desire to garden all year round. And with little use of materials as well as some reuse, building a cold frame is a green project, too!

Feature image courtesy of Ofer El-Hashahar

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Molly Smith

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