Start with a Clean Sweep

By late September, most balcony crops have done their thing. Tomatoes are down to their last few, courgettes have gone leathery, and the salad leaves you sowed in July are bolting. It is tempting to leave everything to collapse quietly over winter, but clearing spent plants now is the single best thing you can do for next year's growing space.

Empty compost from spent crops rather than leaving it in the pot. Old compost becomes compacted and depleted, and any pests or disease that built up over summer will simply sit there waiting. If the plants were healthy, you can refresh that compost with a handful of slow-release fertiliser and a scoop of homemade or shop-bought compost and reuse it for less demanding crops such as salad or herbs. If you had blight, mildew or vine weevil, bin it rather than composting it.

Give your pots a scrub with hot soapy water and a stiff brush, then rinse them well. Terracotta is porous and will hold onto salts and grime, and clean pots dry out better and look far nicer on a windowsill than a row of algae-streaked plastic.

Protect Your Pots Before the Frost Arrives

Container growing has one big drawback in winter: roots are far more exposed than they would be in open ground. A plant in a border has the whole soil mass around it as insulation. A plant in a 10-litre pot on a windy third-floor balcony has almost nothing.

• Raise pots off the ground. Use pot feet, bricks or timber offcuts. This keeps drainage holes clear and stops water pooling underneath, which is the main cause of winter waterlogging.
• Wrap vulnerable pots. Bubble wrap, hessian or old blankets around the outside of terracotta and thin plastic pots will stop the root ball freezing solid. Leave the top and the drainage holes open.
• Group pots together. Clustering containers against a wall or in a corner shelters them from wind and creates a small microclimate. Push the hardiest to the outside edge and the tenderest into the middle.
• Move what you can. Bay, rosemary, olives and other borderline shrubs will fare much better against a sheltered south-facing wall than out in the open. If you have space indoors by a bright window, bring in anything genuinely tender.

Cut back watering dramatically but do not stop altogether. Evergreen herbs and shrubs still lose moisture through their leaves, and a cold, dry compost is more damaging than a cold, damp one. Water sparingly on mild mornings rather than in the evening.

Plant Spring Bulbs Now for a Lift in March

This is the part of autumn container growing that gives the biggest reward for the least effort. Bulbs planted in October and November will spend the winter building roots and then push up flowers just when you most need them.

Use fresh, peat-free compost and plant in layers so a single pot works harder. Start with the biggest bulbs at the bottom: narcissi and tulips need around 15cm of depth, so choose pots at least 25cm deep. Cover with a couple of centimetres of compost, then add a layer of smaller bulbs such as crocus, muscari or iris reticulata at around 8cm deep. Top up and water well.

Cram them in — bulbs look far better planted densely in containers than spaced out politely. A 30cm pot will comfortably hold a dozen narcissi with room for a few dozen small bulbs above them. Add a thin layer of horticultural grit on the surface to deter squirrels and keep the compost from splashing.

Leave the pots outside in a sheltered spot. If you want flowers a few weeks early, bring one pot into a cool, bright room in late January and let it come on gradually.

Keep Something Growing Through Winter

An empty balcony all winter is a wasted opportunity. There is a respectable list of crops that will tick over happily in containers through the colder months, especially in milder parts of the UK.

• Winter salad. Land cress, winter purslane, mizuna and hardy lettuce varieties will keep cropping with a little protection.
• Oriental greens. Pak choi, komatsuna and mustard greens grow fast in autumn and tolerate light frost.
• Herbs. Parsley, thyme, sage and winter savoury all stand up well to cold and wet.
• Broad beans. Sow a hardy variety in a deep pot now for an early crop next summer.

If you have a cloche, a cold frame or even a clear plastic storage box with the lid propped open for ventilation, use it. Just remember to open it on mild days so the plants do not cook or rot.

Feed the Soil, Not Just the Plants

Before you close the door on the season, put something back. Spread a couple of centimetres of well-rotted compost or worm castings over the surface of any pots holding perennials or overwintering crops. It will slowly work its way down and feed the soil life that does the real work.

Consider sowing a green manure in larger containers that would otherwise sit bare. Field beans or grazing rye sown in autumn can be cut down in spring and mixed into the compost, adding organic matter that bagged compost sorely lacks.

Finally, take ten minutes to write down what worked. Which tomato variety actually ripened on your north-facing balcony? Which pot was too small by August? A few notes now will save you a lot of guesswork next spring, and that quiet bit of planning is really what autumn is for.