Garden Cold Frames to Extend Your Gardening Season

By J. Ruppel

We all are looking for ways to get garden crops sooner, or get more of them. One way to get an early jump is to use a cold frame to start your seedlings.

The gardening season can’t start early enough for most of us. For those in the northern states the gardening season seems like it may never start, and it’s just too short for some long season warm weather vegetables like okra or some melons. For those in the south, it would seem that the growing season is long enough, but with the very hot summer months some crops just either won’t survive the heat and dry weather, or even if they do survive they won’t produce much when temperatures get above 80 or 85 degrees. This includes some of the old standby favorites like tomatoes or even bell peppers.

While many vegetables can be started indoors, one problem with doing that is that they get acclimated to either greenhouse or indoor conditions, and can be ill suited to set out early in the season when the night time temperature swings can be at their most extreme, and these tender seedlings can be easily damaged by temperatures close to freezing. One way to help them acclimate is to “harden them off” which is basically a methodology of slowly introducing them to the harsh outdoor environment.

The old standby tool for doing this is s cold frame. A cold frame is similar to a raised bed garden, as it can sit above the main garden, but it is covered with either a poly window or even a glass window.

A cold frame differs from a hot bed in that a hot bed usually incorporates an additional heating source, and doesn’t depend only on the solar heating of the sun shining through the window like a greenhouse. These additional heat sources can be as varied as a simple resistance wire electric heater to situating the bed over a manure pile.

A cold frame can be made from a wide range of construction materials. Probably the simplest might be to stack bales of hay around the bed, and to place a discarded window over the bales of hay. Or instead of bales of hay a wooden box can be constructed to fit the window, and form a tighter seal from outside air. You can improve the performance of the cold frame by adding weather sealing to reduce the air infiltration.

If you are going to be using the frame in some warmer temperatures, it may be best to have the window on hinges so that it can be propped up to allow some air circulation and regulate the temperatures so that the plants inside don’t over heat.

There are many commercial cold frames as well. Some are simple polyurethane tents that fit over just a few plants. Others are large raised beds that actually are designed to stay in place the whole gardening season, with a removable cover that is only there during the colder days of the growing season.

Cold frames can also be used to help perennials over winter in colder temperatures. Cold frames are a great addition to any gardeners set of tools, and can either be made or purchased in a size to fit your specific gardening needs.