How to choose a cold frame

There are so many different designs of cold frame available; using different materials it can be a little overwhelming.

Construction

The initial choice is really between wood and aluminium (or other metal) construction. Wooden cold frames are more suited to a permanent site due to their heavier weight; they are also more attractive in my opinion. Aluminium cold frames are great if you want to be able to move them: to take advantage of the seasonal changes in the suns position for instance. Wood has the added advantage that it retains heat better and will therefore keep your precious seedlings warm well into the night.

Glazing

Traditionally cold frames used horticultural glass however it is pretty rare to find a new one using glass. Modern cold frames tend to use polycarbonate that is considered to transmit light just as well as glass. Glass has the advantage that it is a better insulator. However double-glazed cold frames using polycarbonate are available that mitigate this. The big advantage of polycarbonate over glass is that it doesn’t shatter which is vitally important if you have children or pets. Polycarbonate is also cheaper and lighter than glass.

Design / Style

There are two main designs, those with the traditional sloped roof light and those with sliding roof lights. I prefer the traditional style of cold frame with the sloped roof light as this helps to keep the weather out even when left partially open. Of course the sloped roof is more susceptible to wind than the sliding variety when open. Generally aluminium cold frames are fully glazed (i.e. the sidewalls are glazed) whereas some wooden cold frames have solid wooden walls, giving better night-time heat retention.