A cold frame earns its keep in the smallest garden

A cold frame is little more than a bottomless box with a glazed lid, yet it will transform what you can eat between October and April. Sitting against a south-facing wall or fence, it lifts the temperature a few degrees above the surrounding garden and, more importantly, keeps the worst of the wind, rain and frost off tender leaves. That modest protection is the difference between a soggy, slug-ravaged row of lettuce and a steady supply of crisp cut-and-come-again salad.

You do not need much room. A frame a metre wide and half a metre deep will keep a household in leaves if you sow it in small patches and keep resowing. Even a couple of old double-glazed units hinged onto a timber frame will do the job, and it will pay for itself in avoided supermarket bags of wilted rocket.

Choose leaves that shrug off the cold

Forget the soft butterheads you grow in July. Winter salad is about hardy, fast-growing leaves that tolerate low light and repeated cutting. Sow a mixture rather than a single variety, so that if one sulks the rest carry on.

• Winter lettuces: 'Winter Density', 'Arctic King' and 'Val D'Orges' hold well and heart up in spring.
• Mustards and Asian greens: mizuna, mibuna, 'Red Giant' mustard and pak choi germinate quickly and add a peppery bite.
• Rocket: wild rocket is far hardier than the annual kind and keeps cropping for months.
• Corn salad and claytonia: unfussy, cold-proof and quietly delicious with a sharp dressing.
• Baby leaves: spinach 'Winter Giant', chard and kale 'Red Russian' cut small make a substantial base for winter plates.

Sow little and often for a continuous supply

The mistake most of us make is sowing a whole frame in one go in September, then facing a glut followed by a famine. Instead, treat the frame as a series of small beds. Divide it into three or four sections and sow one section every three to four weeks from late August through to early November. A further sowing in February, once the worst of the cold has passed, will give you baby leaves by early April.

Sow thinly — broadcast seed lightly over raked compost and cover with about 5mm of fine soil or sieved compost. Aim for plants roughly 5cm apart; crowding is the main cause of damping off and leggy, weak growth. If you oversow, thin the seedlings and eat the thinnings. Water gently with a fine rose and label the patch with the date, because in January you will not remember what is where.

Care through the colder months

The single most useful habit is to open the lid on mild days. Damp, still air inside a closed frame encourages botrytis and mildewed leaves, so prop the lid a few centimetres whenever the temperature rises above about 5°C, and close it again mid-afternoon to trap the day's warmth. On very cold nights, an old blanket or a sheet of bubble wrap over the glass adds another degree or two.

• Water sparingly and at midday. Winter compost should be barely moist, never sodden. Check under the surface before reaching for the can.
• Mulch with grit around seedlings to keep leaves off wet compost and deter slugs.
• Watch for slugs and snails with a torch after dark — a few evening patrols do more good than anything else.
• Remove yellowing leaves promptly and clear any debris that could harbour rot.

Cut it right and it keeps coming

Cut-and-come-again works because you harvest the outer leaves and leave the growing point intact. Take a sharp pair of scissors and snip leaves about 3cm above the compost, never right down to the base, and always leave the tight central bud untouched. A fortnight later you will have another cut from the same plants.

Harvest in the morning when leaves are turgid, and take only what you will eat that day. Wash and dry them gently, then store in a lidded box lined with a little kitchen paper. Plants that eventually bolt in spring should be pulled and the space resown — or left to flower, which brings us neatly to the wildlife side of things.

Growing salad alongside the wildlife

A frame does not have to be a sterile zone. Some of the best pest control you can get is free, provided you make room for it. Ground beetles, centipedes, frogs and hedgehogs all eat slugs, and all of them are discouraged by tidy, poisoned, pellet-strewn beds.

• Skip the slug pellets. They harm birds, hedgehogs and pets, and the slugs soon return.
• Leave a wild corner nearby — a log pile, a few stones, a patch of longer grass gives predators somewhere to shelter.
• Let a few plants flower in spring. Bolted mustard and rocket are a magnet for hoverflies and early bees.
• Keep a shallow dish of water at ground level, refreshed often, for birds and insects.
• Grow flowering herbs such as chives and marjoram close by to bring in pollinators and predatory insects.

Do that, and your cold frame becomes more than a salad factory. It becomes a small, busy, living patch that feeds you through the lean months and gives the garden's wildlife a place to overwinter — which is, in the end, exactly what good kitchen gardening looks like.