A COLD frame is an extremely useful tool, writes TOM ATTWOOD. Not only for the spring but at this time of year when colder nights and persistent rain can test the hardiest of plants, especially when they are immature and growing in plastic pots. Cold frames provide a protected environment, not a heated space, but a dry one and that can make the most enormous difference. On the nursery we use a giant version of a cold frame which traditionally are termed Dutch lights. These are large wooden window frames that are approximately 1.8 metres by 1.3 metres. We lay them on concrete blocks (or stacks of bricks) raised off the ground. Although close to the ground it is enough to get them clear of the plants beneath. The plants (on the whole) overwinter beautifully under these ‘lights’ and once more, it is all about that dry cover they get for the best part of six months.

A basic cold frame has its limitations in what you can physically get inside them due to their size but in principle are just as effective as a small unheated greenhouse only they take up a fraction of the space and can be constructed for very little. The simplest method is to arm yourself with an old wooden window that is being removed from a property. The traditional sash window is ideal and very often you can find these carefully stacked up where they are being replaced or placed in skips; but please check they are indeed up for grabs before walking off with one.

The alternative is to construct a basic wood frame and fix to it a sheet of clear Perspex or acrylic that can be screwed onto the timer. The size of frame you make is your choice, but to an extent the space available will dictate this and what you feel comfortable handling, and not creating something too cumbersome.

You then need something to sit your frame or upcycled window onto. A base made from scaffold boards is ideal, but you could buy treated wood of a similar size. Whatever you use you need a base to match the size of the lid. It is preferable to angle the base so that the lid (window) is also angled slightly so that water can run off. Finally, find some robust hinges to fix the window to the base and that essentially is it. I like to have gravel on the floor within the frame to improve drainage. Site your cold frame in a well lit location (west facing is ideal) but not in full sun as it will get too steamy on the sunniest of days and cook the contents.

Next week: planting a new hedge