DIY Cold frame / DIY mini-greenhouse

Repurpose old windows or shower doors to extentend your growing season with this simple DIY cold frame.

When I told people I was going to build a cold frame, most of them asked “A what?”

A cold frame is exactly what it sounds like: a transparent outdoor frame that protects plants from cold weather while still letting sunlight in. The top is usually made of some transparent substance (glass, plexiglass, plastic, etc) that allows sunlight in and traps the condensation inside the frame to help feed the plants.

What is the difference between a cold frame and a greenhouse?

Greenhouses are generally much larger and have a ventilation system to heat and cool the building for year-round growing. Cold frames are smaller and rely on the sun to heat the interior and the earth to hold the warmth.

A cold frame is a simple structure that utilizes solar energy and insulation to create a microclimate within your garden. For those of you who have harvested and eaten a salad of fresh greens in February or have flowers blooming well past frost, you know the attraction of using cold frames. ~FineGardening.com

You can use a cold frame to start seedlings earlier in the Spring, to house dormant plants through the winter, and to extend your growing season by keep frost off of late blooming veg.

The reason I wanted a cold frame?

I had a shower door. 😂

If you follow me, you know I love a good repurpose – I get such a kick out of turning something that would otherwise be landfill into something new and usable. My parents are renovating their bathroom at the moment and had 4 sliding shower doors that were headed to the dump. I jumped all over the opportunity and asked them if I could have them to see if I could repurpose them into something new.

Enter my DIY cold frame / mini-greenhouse.

The shower door I used was 54″ long by 18″ wide. You’ll want to have a slight overhang on all the sides so that rain and moisture doesn’t accumulate on the wood frame, so I build my DIY cold frame to 53″ long by 17″ deep.

To make a DIY mini greenhouse this size, you will need:

(5) pieces “‘x6″ cut to 53” long
(5) pieces 2″ x 6″ cut to 14″ long – one of these boards you will cut in half diagonally
(2) pieces 2″ x 2″ cut to 18″
(2) pieces 2″ x 2″ cut to 12″
3″ deck screws
2 ½” deck screws
(2) hinges

Once you have your 2″ x 6″ boards cut to length, create a frame with two 53″ boards and two 14″ boards sandwiched between them. Build two of these frames using 3″ deck screws.

The last frame will be just three sides – one 53″ board and the two half boards that you cut on a diagonal.

Now you’ll want to place your 2″ x 2″ boards in each corner and draw a cut line for the angle. It should be around 32º, but better to draw it for accuracy.

Insert the four corner pieces inside the frame and attach using 2 ½” deckscrews. These four corner posts will hold all three of your frames together so you can carry and move it.

Pre-drill a hold on the lower side of your diagonal pieces and attach them to the board below with 2 ½” deck screws.

Your DIY cold frame is built – well, the frame anyways.

From here – since I was using shower doors already in a frame – all I had to do was pre-drill small holes in the aluminum frame and attach the door to the mini greenhouse with the screws provided with the hinges.

These shower doors are so perfect for mini greenhouses – they are water-proof so no snow will get in and rot the wood and any condensation that develops as a result of the sun heating the DIY cold frame will drip down into the plants below.

You can see where I kept about a 1″ overhang on three sides:

Oh! I should tell you! I used regular framing lumber to build my cold frame – which is not at all ideal – but I did use an outdoor stain to help prolong the life of the wood. You DON’T want to use chemically treated wood if you are filling this with soil (and not just dropping in pots) as the chemicals will leach into the soil and make you grow a third nipple (or testicle).

Cedar would be the best option, but it’s incredibly pricey at the moment – so I went with the crappiest framing lumber I could find and then asked my home improvement store for a discount. It ended up I got the 2×6 boards for half price, and you can’t tell how shitty they were after a bit of planing and a stain.