Ben Vanheems shares some essential tasks to carry out in your garden and allotment for August.

SOW NOW

Cabbage (spring), carrots, chicory, endive, kohl rabi, lettuce, onion, oriental leaves, rocket, salad leaves, spinach, spring onion, Swiss chard, turnips, winter radish

PLANT NOW

Chicory, cauliflower, endive, kale, rocket, oriental leaves, sprouting broccoli, strawberries, Swiss chard

HARVEST

Aubergine, beetroot, beans (all types), broccoli, cabbage, carrots, cauliflower, celery, chicory, chillies and peppers, courgettes and summer squash, cucumber, Florence fennel, garlic, globe artichoke, kohl rabi, lettuce, onions, peas, potatoes, radish, salad leaves, shallots, spinach, spring onion, strawberries, sweetcorn, Swiss chard, tomatoes, turnips

Keep picking and lifting!

August is the most abundant month of the year, with delicious produce coming thick and fast from just about every corner of the plot! Enjoy this time of plenty, your reward for all that hard work earlier in the season.

Onions are ready once the foliage starts to turn yellow and flop over. Now is also the moment for second early potatoes, with varieties from floury baking potatoes to firm and waxy salad spuds such as ‘Nicola’ and ‘Charlotte’. Maincrop varieties follow next month, but if it is very wet and slugs are a problem start lifting them early to avoid too much damage.

Remember to keep picking those beans! Even if you have had enough of them, picking now will ensure they carry on producing well into autumn, when the pods will perhaps be more welcome.

Check sweetcorn

Check sweetcorn cobs for ripeness. The silks at the end of the cob should be brown. Peel back the husk and sink a fingernail into a kernel – if it exudes a milky liquid, it’s good to go.

Hunt for weeds

Check for weeds hiding among larger vegetables such as squash and pull out any you find. Never let weeds go to seed or you’ll be storing up trouble for future years.

Earth up celery

Gradually mound up soil around developing celery stems to blanch them. Start when they reach 30cm (12in) tall. Celery loves moist soil so water regularly.

Feed squashes

Looking for champion-sized squash or outsized pumpkins? Then feed plants weekly with a liquid tomato feed to help support fruit development.

How to harvest and store onions (step by step)

STEP 1: You can harvest onions once they reach a usable size but if you want to store them, wait till the leaves begin to flop over and turn yellow. Reduce watering in the run up to harvest, stopping entirely the week before. Carefully ease the onions up with a fork.

STEP 2: Leave the onions on the soil surface for a few days to begin drying, then move them under cover to continue. Spread them out on to racks or greenhouse staging to keep them well aired. The onions are ‘cured’ once the skins are papery and the leaves have completely shrivelled.

STEP 3: Store your onions out of direct sunlight in a cool but frost-free place such as a shed or garage. Raise them off the ground in breathable sacks, suspend them from the ceiling in clusters, or try stringing them. Bring them into the kitchen as they are needed.

Sow a green manure

Give recently vacated ground a boost by sowing a green manure. Green manures cover the soil, protecting it from the eroding effects of rain, then contribute welcome organic matter when dug back in. Use deep-rooted green manures like grazing rye to improve soil structure, while legumes such as winter field beans and clovers will fix nitrogen for future crops. Choose a quick grower like mustard to dig in later in the autumn or opt for something hardy like winter tares to turn in next spring. Cut the green manure down and allow the foliage to wilt before digging it in. Leave the soil for at least a fortnight before sowing.

Pests & Problems

■ VINE WEEVILS: Look out for holes notched into the leaves by the adult beetles. The C-shaped grubs feast on roots and are often seen on container plants where they can severely stunt growth. Water on parasitic nematodes from August to October.

■ TOMATO BLIGHT: Brought on by warm, wet weather, blight can decimate tomatoes within days. Pick off isolated infections to slow its progress then harvest any usable fruits should the disease spread. Always water at the base of plants to keep foliage dry.

■ GLASSHOUSE WHITEFLY: These sap suckers can weaken plants and secrete a sticky ‘honeydew’ that can lead to sooty moulds. Check regularly and treat early attacks with an organic spray. Or introduce parasitic wasps, available from online suppliers.

Under cover

Tend to tomatoes

Tomatoes are well and truly in their stride and a little TLC at this stage should see plants continue to thrive and the fruits successfully ripen.

Start by cutting off the lowest leaves. This helps improve airflow around the plants, leaving fewer opportunities for disease. Continue to pinch off the sideshoots from vining tomatoes and, once five trusses have formed, pinch out the very top of the plants. Limiting growth like this forces plants to concentrate all their energy on swelling and ripening the fruits that have already set. Allowing more trusses to form is a risk this late in the summer and will only slow things down.

Pay attention to watering. Don’t allow plants to completely dry out or the fruits may swell suddenly on watering, causing them to split. Irregular watering can also trigger blossom end rot, when the end of the fruit turns black then rots. Help tomatoes develop their fullest flavour by feeding plants when you water.

Grow a pot of carrots

Reuse old compost to grow a pot of carrots to enjoy this winter. Compost left from growing an earlier harvest of container spuds would be ideal. Pick out any remnants of the previous crop then fork over the compost to loosen it up. Fill a container with the compost then top up with a little fresh compost to sow into. Thinly scatter seeds of a cold-tolerant carrot such as ‘Eskimo’ over the surface then lightly cover with more compost before watering. Keep the compost moist and thin seedlings to 5cm (2in) apart. If space is tight, keep the carrots outside but move them under cover when it turns cooler.

How to sow winter salads (step by step)

STEP 1: Sow hardy winter salads and oriental leaves such as mizuna for cutting from autumn onwards. The easiest way to start them off is to sow into modules. Make shallow depressions in which to sow, drop a few seeds in, then cover with a scuff of extra compost.

STEP 2: Thin the seedlings to leave the strongest in each cell then grow on till the roots fill the cell. The young plants can then be planted outside to follow on from earlier crops, ideally under some sort of cloche protection once it turns cold. Or plant into containers to grow in the greenhouse.

STEP 3: Spring sowings of brassicas and some herbs often bolt, but sow leaves such as rocket, mustards and coriander now and you can expect a long harvest. Sow into modules, or direct sow into vacant ground, either outside or under cover. Remove yellowing leaves to avoid attracting slugs.

Start chard for winter

Chard growing in raised beds in the garden

Tuck into more freshly picked greens this winter by growing some Swiss chard under cover, in the relative warmth and away from the prying beaks of hungry pigeons. Sow towards the end of the month, either direct or into small pots or modules to plant into the final growing position within a few weeks. Plant as close as 10cm (4in) for smaller leaves and up to 30cm (12in) apart for bigger leaves. Harvest regularly, taking the outside leaves every time you cut. Growth will slow from early winter then pick up again from around late February as the days lengthen.

Key Jobs for August

■ DETER SPIDER MITES

Don’t let up on red spider mite precautions. The tiny mites struggle in humid conditions, so continue damping down if it’s hot. Remember to inspect yellow sticky traps from time to time to monitor for other pests such as whitefly. Hang them among your plants for best effect.

■ STOP AUBERGINES

Stop aubergines from producing more than six fruits by cutting off any additional flowers that develop. This will encourage all the remaining fruits to reach maturity. Harvest before the fruits begin to lose their shine, which is a sign that they have gone past their best.

■ PICK CUCUMBERS

Water cucumber vines whenever the soil becomes dry and feed regularly. This, along with regular picking, will help plants to continue cropping for longer. Enjoy before they grow too big and certainly before they start to turn yellow or go soft.

■ HELP PEPPERS RIPEN

Nourish sweet and chilli peppers with a weekly watering of liquid tomato feed. Larger plants may need tying to stakes – use enough canes to support each stem so they don’t snap off. For the best flavour, pick peppers once they have fully coloured up; but to extend your chilli harvest, pick them while they’re still green.