Gardening: Coldframes are the way to grow in small gardens

Coldframes owrk like mini greenhouses.

Coldframes owrk like mini greenhouses.

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At this time of year gardeners will enjoy being indoors when the weather is bad, ordering seeds and plants, planning what to grow, and maybe redesigning a new area.

If you grow your own veg and don’t have a greenhouse, consider a coldframe instead – much cheaper and easier to fit into a small garden, even a patio, it can do many of the things a greenhouse can, especially if heated. Visitors to the kitchen garden always admire the span of coldframes attached to our lovely cedar greenhouse.

As with greenhouses the choice is wide and it largely depends on how much you can spend. Basically coldframes are boxes with lids, often higher at the back with sloping sides. Polycarbonate metal framed versions are cheapest; they are light so can be moved around easily, but will need to be securely anchored in position and are the least durable.

Cedarwood frames with horticultural or toughened glass can cost a great deal, but will last longer. The wood turns a lovely silvery colour with age – you often see old frames in Victorian kitchen gardens, still going strong if they have been maintained with a treatment of linseed oil every so often. These heavier frames need to be permanently sited on bases of brick or wood. They can be raised as high as desired provided the base is stable and can take the weight, bearing in mind you’ll need gravel for drainage, plus the weight of pots and trays, as well as compost!

There are many sizes and combinations to be had, choice depends on space available and planned use! Check that lids, or ‘lights’ as they are called, can be adjusted from a slight opening to fully open or removed completely, to allow access and vary openings to suit temperature and weather conditions, and ensure good ventilation. It’s nearly impossible to hold a frame lid open yourself while trying to put trays of seedlings inside!

Siting is important and is usually against the greenhouse sides or a house wall, to insulate one side of the frame and provide shelter from wind, and make it easier to get water or power to them if required. To get maximum light in, a sunny position is best and frost pockets should be avoided. If they are not convenient you won’t use them – so next to the greenhouse if they are planned as hardening-off spaces, or near the house for harvesting if it’s the main growing space.

The bottom of the frame can be open to the garden soil topped up with compost to provide a sort of covered raised bed. Another option is to use soil warming cables as in the greenhouse – heating will extend the range and growing season. At its simplest, a layer of gravel (2-3 inches) to place pots and trays on will give good drainage. My frame at home is raised on a single course of bricks, with ground cover fabric (to prevent weeds) and gravel in the bottom.

I mostly use my frame for growing salads to be harvested in situ, raising seedlings to be planted out, and for hardening off polytunnel-grown plants. A heated frame can especially extend the growing season with earlier sown and harvested veg, e.g. winter lettuce, early carrots, beetroots (bolt resistant varieties) and peas sown in February. Hardening off plants grown in the heated greenhouse is the main role of our kitchen garden coldframes – it’s really important to gradually accustom plants to go outside to the temperature and condition changes so that the shock doesn’t check growth (this can cause bolting/premature flowering).

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