Make a cold frame to extend growing season

Brad and Scott from Buffalo ReUse with cold frameby Connie Oswald Stofko

A cold frame is a terrific way to extend the gardening season. These can be used like  mini-greenhouses during the autumn in raised beds to keep lettuce or spinach growing, and in the  spring to keep tender tomato seedlings warm.

Buffalo ReUse recently held a free workshop on how to build a cold frame.

The workshop was led by Brad Kujawski, left, green space coordinator for ReUse, and Scott Kozak, resource educator for ReUse, right.

If you buy the materials from Buffalo ReUse, it would cost about $20 to build this cold frame, and it would cost more if you buy the materials new.

Here are directions for building your own cold frame.

making the bottom of cold frame in BuffaloFind a window

Find a window sash that is the size you want. The one used by Kujawski and Kozak measured about 26 inches by 32 inches. This window will be the roof of your mini-greenhouse.

You definitely want to recycle a used window for this project, but watch out for a couple of things. Windows with poor glazing may allow the glass to fall out and crush your plants, Kujawski said.

Also, avoid painted windows. The paint may contain lead, which you may not want in your vegetable garden, Kozak said.

Build the bottom of the box

The rest of the cold frame is essentially a box. Start by building a box that is the same size as your window. You should use non-decomposing wood such as cypress or cedar. Buffalo ReUse gets a lot of hemlock wood from old houses, which also works well, Kozak noted. If you’re not sure what to choose, the staff at ReUse can direct you.

You need to cut four pieces of wood to the diagram for building cold frame for garden in Western New York proper length.

What is the proper length? The pieces will be the length and width of your window sash, after taking into account the thickness of the wood. You’ll be butting the pieces together, so some of the pieces will need to be shorter so that they will fit together. (See diagram at right.)

Measure your wood and cut it.

Attach the pieces together using nails or screws. At the Buffalo ReUse workshop, participants had the opportunity to actually work on the project. Above right, Patrick Gooch of Hamburg uses a power screw driver.sawing to make cold frame for garden in WNY

Build the sloped part of the box

You want the roof of your box to be sloped about 15 degrees to let in more  rays of the sun. In this step, you’ll create two triangular sides for the box.

Measure a piece of wood the same length as the sides of your box.

Draw a diagonal from one corner to another. (See photo at left.)

Clamp the piece of wood to a sawhorse. Using a circular saw, saw along the line halfway (stop before you get to the sawhorse.) Flip the wood and saw from the other side to complete the cut.

slanted pieces for cold frame for garden in WNYThe pieces will fit as shown in the photo at right.

You also need to cut a straight piece of wood to fit between the slanted pieces at the back of the box (where you’ll attach the hinges).

Attach the pieces using nails or screws.

adding hinges to cold frame for garden in WNYAttach the window sash

Using a door hinge and screws, attach the window sash to the top of the box. Heather White, visiting from Chicago, takes a turn in the photo at left.

Other tips

  • To make it easier to drive screws into hard wood, use a drill or a  hammer and nail to start the hole.
  • If you paint the inside of the box a light color, it will reflect light and keep the inside warmer.
  • The temperature inside the cold frame shouldn’t exceed 8o degrees Fahrenheit. To vent your cold frame, prop the top open with a stick.
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