A garden without a greenhouse is like a kitchen without an oven: you can’t make the most of your raw materials. It’s so much more pleasant — and productive, too — pottering in a greenhouse than in a shed, which is probably why 50 per cent of readers of Gardeners’ World magazine have a greenhouse. They are such useful things, even unheated. It’s a quiet time in the garden now, just right for putting one up. It’s sale time, too.

I like a greenhouse to be a walk-in winter cold frame, somewhere to keep pots of succulents, tubs of agapanthus, eucomis and lilies, trays of cuttings to pot on in spring, somewhere they can be kept on the dry side and multiblanketed with bubble-wrap when the temperature drops below zero for a few days.

In summer a greenhouse is just the place to grow tomatoes; that extra warmth makes all the difference. Where better for children to see a plant grow from a seed to a juicy fruit in the hand? Early extra warmth lets you give a head start to plants that will spend the summer outdoors: hanging baskets, tubs of cannas, potted dahlia tubers there for a kick-start, seedling plants for the veg patch. In summer you can mollycoddle potted heat-seeking treasures such as Pelargonium ardens and in early spring it’s just the place to rear pots of hyacinths and Iris reticulata, safe from birds and rain.

Construction You can do wonders in a 6ftx8ft greenhouse, but if you want it as a winter storehouse and cosy potting shed then 8ftx10ft is better. A metal frame lasts longer than wood but always looks more alien in a garden, even when the shine has faded. Polycarbonate is cheaper and lighter than glass, but eventually it discolours. A greenhouse with curved shoulders (where wall meets roof) will direct all the rain to the ground. If you want gutters and a water butt you need a roof with an overhang.

Don’t skimp on roof vents and to avoid high temperatures on hot days make sure that some are automatic. Have plenty of vents low in the walls to create a good through draught. Check that the door is high and wide enough for you. Some models have a 5in threshold, others almost none, so think about wheelbarrow access.

Where to put it Good light is essential; if it gets too hot you can put up shading, but you can never replace lost light. Shade often means trees, and trees mean insects and dirty glass and less light. A position tight to a fence means that you can’t clean or repair the back.

A lean-to greenhouse built against a garage wall will be warmest in winter. Also consider whether it is near enough to the house to lay on water and power for an electric propagator or occasional heating.

How to put it up If you are patient and good at DIY it’s easy enough to do by yourself, with occasional help. Take your time. Read and reread the instructions. A professional will do it with embarrassing ease and speed.

summergreenhouses.co.uk

greenhousesdirect.co.uk

Explore Gardens

• Hampton Court Palace Flower Show

• Chelsea Flower Show

Times recommends

• Second homes: credit crunch casualty or money-spinner?
• How I built my own sliding house
• Top 10 incentives for house buyers