I built this cold frame in January with a lot of help from my friend David Peterson who built a duplicate model for himself at the same time.  David is retired, lucky guy, and he has put together a really well equipped workshop with lots of woodworking equipment to keep occupied.

We were discussing cold frames over dinner quite a while back and I let David know that I had a whole lot of 1/4″ clear glass sheets about 2 feet by 6 feet that I thought might be good for making a cold frame.  David let me know he was interested and kind of pushed me along until we got the project done.

We essentially built the frame to accommodate the glass.  The wood frame for the glass is simple 2 x 2 framing lumber that has been routed along the center to receive the glass. It is held together with simple screw straps at the four corners.  We put narrow slits at the lower front edge of the frame to allow water to weep so it would not collect on the glass when it rains.   The glass frame is secured to the base with three 2 1/2″ wide hinges.

The base is 1/2″ plywood with 1″ insulating foam glued to the inside.  The frame slopes from 14″ in the back to 8″ in the front.  Its all held together with wood screws and L-brackets.  I put a coat of paint on it, but I’m not entirely sure that was a good idea.  (Leaching?). David has rigged up a venting device that uses dowels to hold the glass open at various positions, but I haven’t finished my venting prop, yet.  In the short run, I’ll just use different height pieces of wood.

Right off the bat I can say the 1/4″ glass is way too heavy.  The price was right (free), but the 24″ width of the frame is too narrow and the glass, at three pounds per square foot, makes moving the frame and opening it up a bit of a chore.  If I work with glass again, it will be 1/8″ or thinner, but I’ll probably look at using polycarbonate sheet that will be lots lighter and have better insulating capabilities.  The lighter plastic will possibly allow me to consider using a thermostatically controlled venting device.  I’d need a huge electric motor to lift up the glass on this model.

Nevertheless, I have a cold frame to play with and I’ll be putting it to work next week.  I plan to direct seed salad greens, and maybe use it to start some veggies for transplanting.  I’ve been monitoring the temperature. It got up to over 120 degrees F with the lid closed so that means I have to be checking it frequently, or I’ll either cook or freeze my plants.

I should have put together some cold frames, years ago, but I expect to knock out several more of these this spring so I can extend my growing season in spring and fall.  I’m hoping to get about two weeks to a month more outdoor production of salad greens on either side of the normal unassisted growing season.