Cold Frame for March Days

The month of March brings the promise of spring and warmer days. Early bulbs and perennials peek through the ground. Leaf buds form on trees. Birds' activities heighten as they position themselves for their favorite nesting sites. It is clear that the promise of spring will be fulfilled for the new year. But March days can also turn dark and cold, bringing killing frosts again.

A well-planned gardening calendar is very helpful, but can only be used as a rough guide. Last frost dates must be kept in mind and restraint used. A big mistake new gardeners make is to remove protective mulch or set out plants too soon.

One accessory for the garden which can be invaluable is the cold frame. Herb seeds can be sprouted indoors and then taken out into the cold frame where they will get enough light. Plants can be kept in the cold frame until after the last frost date. A simple cold frame is easy and inexpensive to make, and can give a gardener years of use if dismantled and stored when not in use.

A cold frame is basically a box with a lid, and with this particular example, the box is made of one piece of 3/4" 4x4 plywood, the lid with 1x2 pine.

Materials Needed:

(1) 3/4" exterior grade plywood, 4'x4' (for box)
(2) 2'x4' pieces of plexiglass (for lid)
1x2 pine: (2) 48" pieces (2 sides); (3) 44" pieces (2 sides, one middle brace)
(12) 2" corner brackets (4 to attach lid pieces, 8 for box sides- 2 on ea. corner)
(2) 4" strap hinges (to attach lid to box- bend top over to fit to lid)
3/4" round head brass wood screws (to attach plexiglass) 3/4" flat head wood screws (galvanized)
(2) 2 1/2" screws (to attach middle 1x2 piece to center of lid frame)

Directions:

Cut plywood as shown. Put together box with 8 corner brackets, two on each corner, with the 9x48" piece as the front, the 15" high piece as the back, and the two angled pieces as the sides. (See picture)

Put the lid together using the two 48" and two 44" 1x2 pine and corner brackets. Attach center piece with long screws. Pre-drill plexiglass and attach to lid with brass screws. Screw 12" 1x2's to opposite sides of inside of box to hold lid open for ventilation purposes.

A word of caution: the sun can be VERY hot, especially shining through the plexiglass. If the forecast predicts a warm sunny day, the cold frame lid will need to be opened all the way. Check seedlings constantly for moisture content, as potted plants will dry out rapidly.

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