Build a Small Cold Frame

The plant holding area in my nursery is terraced into two section with a two foot retaining wall between them.  The wall makes a right angle on one side as the lower terrace is sort of cut into a sloped area but only two feet.  This northwest corner was where I built a small greenhouse in 2010 and used last winter for many of our tropical plants and to store freshly dug bamboo plants in the winter.  I like digging in the winter and with a greenhouse the plants really handle the shock well.  The greenhouse was well insulated and cost very little to keep heated to above freezing,  but Mickey and I decided it just didn’t look good, especially in the winter with no leaves to help hide it.  So when summer came, we disassembled it and saved most of the material (steel hoops, insulation, plywood, and framing lumber.)
This year I decided to build a small cold frame to store our tropical plants.  We grow and collect elephant ears, banana trees, gingers, and we mulch most of them in the winter.  When spring comes, we are anxious to get our gardens growing so I really like having a number of plants ready to grow as soon as all danger of frost is past.  I counted about 40 to 50 large plants I’d like to dig. We will cut off the foliage right before the first frost, pot the rhizome or tuber or whatever and this year place them in a well insulated cold frame.

Completed Cold Frame

Materials Needed
2 x 4 lumber – decay resistant
Rigid foam insulation, foil on at least one side
Deck screws
Roofing nails
Polyethylene sheeting
Stapling tape or thin wood strips
to hold plastic sheeting
Landscape fabric if needed

The lengths of lumber, size of poly sheeting, and number of sheets of insulation depend on the size of your coldframe.
Having a retaining wall with a corner that  I could use as two sides of the cold frame gave me a very stable and strong place to attach the other two side.  I used the 2 x 4′s turned on their sides as framing for the base.  My retaing walls are 24″ so I used the same height for the south and east walls.  After building the long wall, using decking screws instead of nails, I stood it up and used a piece of scrap 4 x 4 for the corner.  The long wall is on the south side.