Don’t leave your greenhouse standing empty over autumn and winter. The protection it provides will not only help you to keep tender plants frost-free – it will also let you grow hardy crops, such as salads and herbs, all winter.
An unheated greenhouse can keep overnight temperatures as much as 5°C warmer than outside, which will keep plants frost-free in all but the worst of winters. It will also ensure plants stay dry, which greatly aids survival. A dry plant is much less likely to freeze than a damp one. It is often the combination of cold and wet that kills borderline-tender plants outside over winter.
The main consideration is to make sure your plants get plenty of light, as natural light levels are low in winter. Remove any shading material and clean the glass to maximise available light.
The following plants are all ideal for growing in a cold greenhouse through autumn and winter.
Try hardy lettuces, such as ‘Salad Bowl’, as well as rocket, pak choi, mizuna, lamb’s lettuce and spinach. Sow in trays or pots of compost, then plant seedlings into large containers, border soil or this year’s old growing bags. Find out more about growing winter salad.
Pot up chives, parsley and mint in autumn and bring them into the greenhouse, where they’ll continue growing all winter. It’s worth planting up several pots of each, so you can harvest them in succession for a continuous supply. Watch our video guide to growing herbs in a greenhouse in winter.
Lift a rhubarb crown in autumn and leave it on the soil surface – it’s hardy enough to survive being frosted. Bring the crown into the greenhouse in late December and cover with a large tub to exclude light. Pick the stems when 30cm long.
Peaches and nectarines
Prone to peach leaf curl fungus, the foliage of both plants can be kept disease-free if planted in the border of a cold greenhouse in autumn, or grown in pots that are kept under cover between October and late March. Read our peaches and nectarines Grow Guide.
Although most are hardy, alpines benefit from protection during wet weather, as this spoils the flowers and encourages rotting. Bring plants indoors over winter, then move them outside again once the flowers fade. Discover 10 alpines to grow.
Pot up tulips, daffodils and hyacinths in autumn and stand them outside for six weeks. Then bring into the greenhouse to encourage early blooms. When buds appear, take the pots into the house and enjoy the display. Discover nine spring bulbs to force in autumn.