If we’re lucky September will treat us to an Indian summer, but even if there’s plenty of warm sunshine there’s no escaping the changing seasons; the autumnal chill on dewy, misty mornings and the shortening days. Gardeners know these are the signs to start planning for next year.
It’s easy to think greenhouses are for spring and summer growing only, but they’re invaluable at this time of year too. The shelter and warmth inside are ideal for sowing a batch of fast-growing crops for late autumn and winter harvests. Beds in a greenhouse which have been cleared of summer crops can be refreshed with the addition of some new compost and a sprinkle of seaweed feed or chicken manure pellets; large pots and deep wooden boxes are a good alternative if you don’t have these beds. Sow seed of winter hardy crops such as mizuna and mustards, which are great in stir fries, and winter salads such as rocket, lambs lettuce, green salad bowl and pea shoots.
If you haven’t done so already, there’s still time to take cuttings of borderline hardy perennials like penstemons and tender plants like pelargoniums; these can be used as extra plants next year and will also provide insurance against any losses of the parent plants over winter. Take plenty of cuttings as not all will produce roots and some may develop rot over the winter – you can easily fit four cuttings around the edge of a 9cm pot. Place the pots on a heated propagator base, if you can, to speed up root formation.
Sowing certain hardy annuals in early autumn is a good idea too. They can be sown direct into the ground, but I’ve found they struggle in wet winters, especially if it’s mild enough for slugs to still be active. Having a greenhouse though makes all the difference to successfully over-wintering these seedlings. Summer flowers like larkspur, wild carrot, cornflowers and scabious can be sown into module trays now and they’ll germinate, then grow slowly over the coming months. In spring they can be planted out into the ground where they’ll shoot away and produce an early display of flowers.
I live somewhere that gets a lot of rain over winter so I like to use an unheated greenhouse or cold frame as a place to shelter delicate spring bulbs which I’ll pop into pots in September and October - bulbs like fritillaries that don’t like to sit in soggy compost. And a cool greenhouse is the ideal winter home for pot-grown citrus trees.
Heating a greenhouse so that the temperature inside is kept above freezing makes it possible to overwinter tender succulents and exotics like bananas. If you have an electricity supply to the greenhouse a simple electric fan heater with a thermostat is the easiest form of providing some extra warmth. If you don’t have electricity then there are gas and paraffin heating options.
So make the most of your greenhouse this autumn and winter, filling it with tasty crops and nurturing plants for next year.
Words and images by Louise Curley