These directions summarize some supplies and steps we have found helpful when working with cold frames. This information is offered for use at your own discretion, and it may or may not be applicable to your specific project. Please consult a professional for more detailed advice regarding your project.

A cold frame is a raised flower bed with a clear covering on top, at an angle, to maximize sunlight. It’s designed to start seeds, even if the weather is cool; keep wind and cold out; and keep the soil warm before the warm season kicks in.


-20’ of 2x6s (or 2x4s, 2x8s, 2x10s or 2x12s)
-window sash
-two hinges
-two handles
-wood screws
-drill driver
-two pieces of any-sized, sturdy wood to prop open the cold frame
-safety glasses
-tape measure
-carpenter’s square



  1. Find a salvaged window sash for your cold frame
  • You can use vinyl windows
  • Wood windows are a good option because it’s easy to screw into them
  • You can also cover your cold frame with a plastic piece, so long as it’s thick enough that adverse weather won’t puncture it
  • Avoid windows that have UV protection
  • Approximately 3′ wide is a good size for the window and cold frame, as it allows you to easily reach inside it and move around it
  • If you decide you want a large cold frame, put pavers down inside it, so you can move around in it without crushing your plants or packing your soil down unnecessarily


  1. Prepare the window sash
  • Clean off any dust that might block sunlight
  • Test the window for lead-based paint. Second Use highly recommends avoiding lead-based paint, especially when close to foods. If you choose to use a window with the lead-based paint, cover it with a safe paint to encapsulate the toxins
  1. Acquire approximately 20’ of 2×6 salvaged lumber
  • Cedar or redwood are more rot-resistant than other kinds of lumber
  • Regular salvaged lumber used in a cold frame should last about five years
  • Other good sizes for lumber include 2x4s, 2x8s, 2x10s or 2x12s, with the higher numbers being a little better. Avoid 4x4s
  • The lumber should be untreated
  1. After measuring the window sash, cut the lumber into side and end pieces that together will create a frame of the same size as the window
  1. Screw the pieces together to create a box with no bottom
  • If the wood cracks, predrill the holes
  • Staggering the pieces of wood will create the strongest box
  • If you’re working with shorter screws, you can drill them in at an angle, to secure one piece to another (With long screws, you can drill them straight down)
  1. Cut two pieces of your lumber at an identical angle, to create the sloping effect of the cold frame
  • Some sources say the lowest part of the angle should be 4” lower than the highest part, in order to maximize sunlight
  • Exact measurements can vary, but the slant should be deep enough that rain water will run off of it
  1. Stack the angled pieces of wood on top of the base layer of the cold frame and secure them with wood screws
  1. Measure the remaining ends of the cold frame and cut the lumber to fill in the gaps
  • You may choose to put small pieces of wood in the corners to support the structure and give you something to drill into
  1. Screw the two hinges onto the tallest end of the cold frame and the window sash
  • The window sash should open toward the tallest end of the cold frame
  • The window sash should fit snugly against the frame
  • Door hinges work well because you can pull out the pin and remove the whole window, if you’d like, rather than having to unscrew the hinges
  • If possible, get galvanized hinges to prevent rusting
  1. Drill the two handles into the sides of the cold frame
  • This will allow you to more easily move the frame into storage during the warmer months
  • Choose handles that are sturdy enough to carry the heavy lumber
  • You may also consider adding a casement window arm to the side of the cold frame, which will allow you to lock up the cold frame, if you have a problem with raccoons


Cold frames allow a person to have a controlled growing environment, but one must carefullymonitor them, to ensure the environment is correct for the plant

  • Buy a normal or soil thermometer (a little more expensive) to monitor the temperature
  • Check the temperature daily at first and continue to check it every few days as the season goes on
  • Temperatures too hot can burn the plants, and too much wetness can cause rotting
    • If the cold frame is not draining well, especially if it’s the rainy season, mix in sand or gravel
    • If the cold frame is getting too much light and/or heat, mix white paint and water together and lightly paint the glass in the window sash
  • Use strong sticks or scrap wood to prop open the window sash, allowing for cooler temperatures in the cold frame
  • Temperatures can vary even within a person’s yard, so it’s wise to keep a garden journal
  • The plants will create transpiration inside the cold frame. In addition to monitoring the temperature, keep an eye on the wetness of the cold frame

To increase warmth around the cold frame, there are a number of options

  • Put woodchips around it
  • Place it up against a house or fence to block the wind
    • If against a cool surface area, like brick, keep the cold frame a couple inches away and put woodchips in between the cold frame and the wall)
  • Put a bamboo mat over the whole cold frame, especially when anticipating a hard freeze
  • Line the cold frame and fill in any gaps with roofing felt or wool
    • Do your best to create a strong seal during the building process. This will lock in heat and also help to keep bugs out
  • An old-fashioned method to increase warmth in the cold frame is to use manure.
    • Horse or cow manure is the best option; chicken manure gets too warm
    • Let the manure sit for two weeks, mix it with soil, and water it well before being put it into the cold frame
    • When putting it in the cold frame, pack it down well with a shovel

All plants are different, but some need a longer growing season and work especially well in cold frames

  • Peppers and basil are good examples
  • Some examples of crops that can grow in cool weather, for instance in the fall, are lettuce, collared greens, broccoli and brussel sprouts
  • Hardwoods or softwood cuttings can also get started in a cold frame
  • If a plant typically grows well on its own don’t put it in a cold frame. Some examples are peas, onions and cilantro
  • You can even grow tropical plants in Washington, so long as you monitor the temperature carefully

There are a number of factors to consider in the placement of your cold frame.

  • The cold frame should go in the south part of your garden to maximize sunlight
  • If there isn’t a good spot in the south part of your yard, just choose the next sunniest place
  • Leaving the cold frame bottomless allows you to put it over a tilled plot in your garden. With handles, you can easily remove the cold frame if/when the plants can stand on their own
  • If you’d like to place it on grass, put a couple layers of cardboard, newspaper or burlap to serve as a weed barrier. Avoid glossy finishes