Plant overwintering onion sets in late September.

Spring cabbages that were sown last month are probably ready for planting out. Cover them with horticultural fleece or netting to stop the pigeons shredding them.

Dig up potatoes before slug damage becomes a problem. Leave them out to dry for two to three hours before storing. Only store sound tubers in paper sacks or boxes.

Regularly pick fast maturing vegetables, such as French beans, runner beans, courgettes, cucumbers, peppers and tomatoes, to prevent them becoming stringy, tough or bitter and to encourage further crops.

Remaining outdoor tomatoes should be picked by the end of the month and ripened indoors. The whole truss can be cut off to allow the fruits to ripen ‘on the vine’, perhaps under a cloche or on a windowsill. Any green fruits can be used in chutneys.

Aubergines may still be cropping in the greenhouse. Pick them once the fruits have coloured, but before the skins start to wrinkle.

Lift onions and shallots once the foliage has started to die back. Do not be tempted to bend over the tops by hand as this can reduce their effective storage time. Allow them to dry on the soil surface if weather permits, otherwise dry in a well-ventilated shed and store in a moisture-free place. Thick-necked onions should be used rather than stored, as they may be prone to rots.

In cold districts, carrots, beetroot and turnip are best lifted and stored for use over the winter. Only store intact roots. Parsnips should be left in, as they taste better once frosted.

Harvest sweetcorn as it becomes ripe. Push a fingernail into the kernel when the tassels at the end of the cob start to shrivel and brown. If the liquid looks milky, they are ready.

Any remaining globe artichokes should be harvested now, before the buds start to open.

Marrows, pumpkins and squashes may be ready for harvesting. Leave them in the sun, or in a greenhouse/garage, to let the skins harden and dry off, before storing them in a cool, dry, dark place.

When asparagus foliage turns brown, it is time to cut it down. Take care of the spines, and give the plants a good mulch afterwards. Any new asparagus beds can be prepared at the same time, adding grit if your soil is poorly drained (e.g. heavy clay).

Celery can be earthed-up for the final time this month, leaving just a tuft of foliage sticking out of the trench or collar in order to blanch the stems. Self-blanching types are less hardy, and should be harvested before the first frosts. Trench cultivars can be left in the ground, although do have some horticultural fleece or straw handy to throw over the tops if severe frosts are forecast in your area. Beware celery rash when handling the plants, especially in sunny weather - gloves and long sleeves are necessary.

Irregular watering can lead to problems with blossom end rot on tomatoes, splits in root vegetables and pea and bean flowers aborting. Help prevent this by watering during dry spells. Recycled grey water is not recommended for edible crops, but stored rainwater is ideal.

Keep up too with watering winter squash and pumpkins: this will prevent their growth from being checked. Use stored rainwater wherever possible.

Sow green manures, such as mustard and Italian ryegrass, to prevent autumn weeds establishing and to act as a soil improver once dug in during winter or spring. Alternatively, place black plastic over bare ground after clearing old crops to suppress weed growth.

Pest & disease watch

Keep up with potato blight and tomato blight control. Outdoor tomatoes are more vulnerable than greenhouse ones. Blighted potato haulms can be cut off and burnt, or placed in the rubbish. The tubers can still be harvested. Precautionary spraying may be beneficial, if the weather is conducive to fungal spread; suitable products are Bordeaux Mixture, Dithane 945 and Murphy Traditional Copper Fungicide.

Potato powdery scab is prevalent in wet weather at this time of year, especially on clay soils. Dispose of affected tubers and rotate crops to prevent the problem building up in the soil.

Common scab and other potato skin problems can be prevalent in dry Indian summer weather, particularly on well-drained sandy soils. Watering is key, and the use of acidic fertilisers may help if you have alkaline soil (which worsens the problem).

Be sure to clear debris created when lifting potatoes, and take care not to damage the haulms. Potato debris left out in wet weather could cause the development of fungal diseases such as black leg or fluffy grey mould.

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