Cold frames & small greenhouses: how to extend your UK season

Our growing season is short and our springs are fickle. A cold frame or small greenhouse is the cheapest way to stretch it: a few degrees of warmth and shelter from wind and battering rain lets you sow earlier, harden seedlings off gently before they go out, and keep picking salad well into the cold. Autumn is the clever time to buy one — you'll want it ready for next spring, and it earns its keep overwintering hardy crops too.

Start with the smallest thing that solves your problem. If you just need somewhere to harden off and protect a tray or two, a cold frame or a little walk-in 'grow house' does the job for very little. If you want to grow tomatoes under cover and potter in the dry, that's when a proper greenhouse earns its space.

Glazing: toughened glass is clearest and lasts longest but costs more and can break; twin-wall polycarbonate is lighter, safer near children, insulates better and won't shatter — my pick for an allotment, where the wind likes to test things. Frame: aluminium is light and rust-free; treated timber is warmer to look at and easier to fix shelves to. Ventilation matters more than people think — look for an opening roof vent or louvre, because an unventilated greenhouse cooks in June. And whatever you buy, anchor it: an allotment greenhouse that isn't bolted or pegged down will eventually go for a walk in a gale.

Pair it with a heated propagator for the earliest sowings and you've got a proper little production line from January onwards — there's a guide to those below.