August polytunnel
August brings baskets of tomatoes, fresh-picked corn cobs, cucumbers, peppers, melons, aubergines and much more besides. Enjoy it all! This is a time to appreciate what a wonderful space the polytunnel is. Even if it’s hard to know what to do with all the produce, keep picking so that plants keep producing. Get out the preserving and freezing books or give the surplus away to friends. It shouldn’t be hard to find a stand-in gardener for August holidays – all those tasty pickings soon repay for a bit of watering.
Weather report
How we always long for a glorious August! Maybe, just maybe, an anticyclone will persist and keep temperatures high. But a wet July can lead to a wetter August. On top of that, the days are shortening and real sunshine can be in short supply. Have faith! This month often seems to turn itself round: a bad start to the month can improve to give bright sun and clear skies.
Some people consider August the first month of autumn. It can certainly feel that way for northern gardens. Night temperatures can start to dip and heavy dews in the morning might mimic a frost, even though the real thing shouldn’t happen for a while yet.
Pot on seedlings until ready to plant out
Keep sowing for winter crops
Feed ripening crops
Check for ripe sweetcorn cobs
Keep foliage away from the polythene
Damp down paths and spray overhead to bring temperatures down
Ventilate continuously
Harvest regularly
Use the glut
Watch out for pests and diseases
Enjoy what you have achieved!
Keep sowing salad leaves
Time to sow
French beans
Kohl rabi
Swiss chard
Winter lettuce
Spinach
Florence fennel
Rocket
Mizuna
Mibuna
Lamb’s lettuce (corn salad)
Land cress
Winter purslane
Texel greens
Spring cabbage
Pak choi
Turnip
Kale
Oriental salad leaves
Potatoes
Calabrese
Beetroot
Pak choi
August sowing
• If you made lots of winter sowings in July, there may be no need to make many more in August. On the other hand, a second sowing staggers crops so that they don’t all become ready at once and also provides some protection if the first sowing fails. It’s always worth sowing a few things this month to ensure there are plenty of crops to pick right through the winter and into spring. Start the process early in August if you didn’t make sowings last month.
• French beans sown early in August can sometimes produce a successful autumn crop, provided there aren’t any really low temperatures to contend with.
• Sow ‘Snowball’ turnips and a winter-hardy variety like ‘Noir d’Hiver’ this month. Sow seed in shallow drills 30cm/12in apart. These will give a good crop of creamy roots in the winter.
• Try sowing pak choi in a pot, to plant out and grow on in the polytunnel. This will suffer if there are really low temperatures, but it often provides good pickings up until Christmas.
• Sow perpetual spinach now, for a continuous supply through the winter.
• If greens are a favourite, now is the time to make a second sowing of spring cabbage. Sow seed in tubs and keep young plants in a holding bed or large container until space is freed up by clearing summer crops. Spring cabbage grown in a polytunnel is always sweeter and less tough than that grown outdoors.
• Winter varieties of lettuce do very well from a late August sowing, as do most salad leaves. For a few different lettuce varieties, try ‘Cassandra’, ‘Winter Crop’ or any hardy variety that catches the eye. Most seed catalogues offer a wide range of salad and oriental leaves. Any of these are worth trying and it can be a way to find a star performer. Maybe some will fail from a late sowing, but you will lose little by risking a small pinch of seed. Cut-and-come-again crops should be sown directly where they are to grow. These do really well in large pots as well as in the ground.
• Florence fennel is an excellent winter crop. Sow early in August and, in all except the hardest winter, it should keep growing through until the following spring. Start seeds in deep pots with a bit of warmth. Watch out for earwigs and slugs.
NOTE: A prolonged spell of temperatures below 0˚C/32˚F will cause fennel leaves to flop. If it is really cold for a long period, then you might lose the whole crop.
• For beetroot lovers, it’s worth making an early August sowing to grow on in the polytunnel. This will produce a crop of tasty small roots in the winter, or early spring if growth is slow. Either way it will be there when outdoor crops are gone. If space is limited, sow seed in cells and plant out, at 12cm/5in apart, as room clears.
Young plants
Some of last month’s sowings may be ready for planting out now. Alternatively, move them on into larger pots, while waiting for space to free up. Try not to disturb the roots too much. Use a kitchen fork to free up the root ball if seedlings are stuck in pots. Winter crops need to be got into the ground as soon as space clears, as they need to get plenty of growing done before colder weather rolls in.
Young kohl rabi plants
Food for growing plants
Apologies for repetition about liquid feeds, but applying them is an important summer task. Plants can crop over many months and they have to be fed well throughout that time. If one batch of feed is used up, make another – it will still be needed next month. There are many good feeds available commercially (preferably choose organic options, such as seaweed-based ones). For home-made brews, see Part 7.
• Tomatoes can be fed every seven days while fruit is swelling and ripening.
• Cucumbers, peppers, aubergines and melons appreciate a feed every ten days while bearing fruit. Any plant that has yellow-tinged leaves is probably short of nitrogen and a liquid feed might provide a quick fix.
• Remember that anything grown in containers or growbags will have a limited supply of nutrients. Most compost will provide enough for about two months’ growing (depending on the size of the plant and the container). If leaves start to discolour, apply a liquid feed and add a layer of compost around the plant.
Top Tip
Top dressing is a useful way of feeding large plants in pots. Scrape back and remove any loose compost before applying a new layer. Take care not to damage roots in the process.
Tomatoes
• Beefsteak, cherry and medium varieties should all be dripping with ripe fruit in August. Harvest regularly and always before fruit bursts or falls to the ground.
• Tomato varieties that have short trusses, of six or seven fruit, can be left to ripen so that the whole ripe truss can be picked as one. This looks decorative and can be an advantage if your aim is to sell surplus produce. Don’t try ripening the whole of a long truss: the top fruit will become overripe and fall before the lower fruit is red enough.
• Side shoots grow from every angle and it is easy to miss them among the foliage. Keep nipping them out and watch for the ones that grow from the base of the stem. Try to keep on top of things, but don’t panic if side shoots start to win the battle – tomato plants will do fine if left to grow at this point, and something can be said for letting fresh new leaves take over the job of old diseased ones. They may create a bit of a jungle, but they will still crop well into the autumn.
• Try to tie tomato stems away from the sides of the polytunnel, so that leaves, flowers and fruit don’t get squashed against the polythene.
• Check for caterpillar damage. If there are holes in fruit, look in and around the leaves near by to find the culprits. There probably won’t be more than one or two and these can be removed.
• Tie in the stem to provide support and feed every seven days.
• Always remove any diseased and discoloured foliage. Keep removing lower leaves to allow light through to ripening fruit.
• Keep the soil damp, to help your plants produce plenty of blemish-free fruits.
Top Tip
One option is to nip the growing point out after four or five trusses are set, to ensure that all fruit ripens well. I prefer to leave plants to grow on unrestricted. Often they set seven or even eight trusses on cherry varieties. If plants ramble, simply tie them on to the next cane along, or the one after that. It may look a little unruly, but you’ll get more fruit. Plants that are stopped finish cropping earlier. I love the possibility of picking the last ripe fruit up to Christmas if the year is kind.
Beefsteak tomatoes
What to do with surplus tomatoes?
Get out the recipe books and start cooking, because August can bring fruit by the basketful. Sauces, soups, etc. freeze well, and so do whole tomatoes if there isn’t time to do anything else. Tomatoes can be frozen whole on trays and ripe trusses of fruit can go into the freezer straight off the plant. Bag these up once they are frozen and use as needed. They will provide a fresh tomato taste, if used in cooked dishes, and you can make chutneys with frozen fruit when the timing suits.
NOTE: Frozen tomatoes soften when thawed and will not be the same as fresh fruit.
Tomatoes can be frozen whole
Cucumbers
Stems may well have grown to touch the top of the polytunnel this month. Some people like to cut the tops at this point, but it works well to simply turn them around so that they grow back down. Take care not to break the stem where it turns and the bumper crop of cucumbers should continue. Stems need plenty of support, so keep twirling them around strings or canes. Use string to tie stems in if they start to slide under the weight of the crop.
Cucumbers in growbags need regular feeding and plenty of water to keep these thirsty plants producing. If the growbag compost is depleted, simply punch a few holes through the base, so that the roots can feed off the soil below (lift the bag carefully, if necessary, and then lay it back down over a layer of compost or manure).
If fruit tastes bitter, check the seed packet, as the plant may be a variety that demands the removal of all-male flowers. It’s not too late to start doing this, but take care to remove every one, preferably before it opens, and preferably every day.
Watch out for signs of mineral deficiency and use a seaweed foliar spray, in the morning or evening, to give a quick feed. Liquid feeds can be watered round the roots every ten days.
Remember to keep harvesting cucumbers, no matter how many that may be. The plants may have pauses in productivity and they will eventually slow down altogether, but the aim is to keep them fruiting for as long as possible.
Melons
Keep twirling the stems around support strings and use nets to support swelling fruit. Check fruit for ripeness, but don’t bruise it by squeezing too hard. Try to get the right balance between watering enough to keep fruit swelling and maintaining a free-draining root run. Earth up around the base of the stem, with fresh compost, to help stimulate new root growth.
Melons will only give bumper crops in a hot summer. In a dull, cold year, plants struggle to put on adequate growth and the fruit that sets may never achieve a decent size. If no fruit has set by August, things might not look too promising. However, if plants are strong and growing well, keep pollinating the flowers, as an Indian summer might see some perfectly respectable fruit in a few weeks’ time.
Nets supporting melons
Sweetcorn
Plants sown in April should be tall and sturdy with swelling cobs in leaf joints. The number of cobs on each plant will vary. This can be due to factors within your control, such as the variety, how early seed was sown or feeding regimes, but it can also be a matter of luck and how much sunshine any summer brings. If a variety regularly gives two or more cobs, make a note and stick with it. Growing in a polytunnel is all about maximizing the crop that you can get from your own particular space.
Corn becomes ready in a glut. Eat it fresh every day for a couple of weeks, with no more than half an hour from garden to pan. Make sure you pick cobs at the right moment, when they are sweet and juicy. Strip away the husk and silks, evict any earwigs and cook the cobs in a pan of boiling water for four minutes – that’s all it takes to serve up delectable corn on the cob (of course a slather of butter and a sprinkling of pepper can enhance the taste too).
Leave ripe cobs unpicked and they will become starchy and far less sweet. Sweetcorn is a real taste of the summer, so binge and enjoy – don’t let any of those golden beauties go to waste.
Sweetcorn
How to check if a corn cob is ripe
• A ripe cob should be fat and firm.
• Check that the silks on the end of the cob have turned brown and started to shrivel.
• Peel back the end of the cob to expose a few kernels. Press with a thumbnail to burst a kernel. If the fluid is milky and thin, the cob is perfect to pick. If the fluid is clear, it’s still too early. If the kernel is dry, the cob is past its best.
• It’s better to err on the side of early picking than to leave the crop to turn to starch. If a cob looks OK, pick it, cook it and eat it. If it is slightly unripe it will still taste good, but leave other cobs to ripen for a few more days.
Top Tip
Some cobs will not have a full complement of kernels. This will have been determined weeks ago when pollination took place. Never leave cobs on the plant in the hope that they might grow more kernels. It just doesn’t work that way. A half-filled cob still tastes pretty good!
Winter potatoes
If you planted a few seed potatoes at the end of July, they should produce plenty of green leaf this month. There is still time to plant a few potatoes in containers in early August, but crops will be smaller.
Keep earthing up around the stem as plants grow; use compost to top up containers. The more stem that is buried, the less chance there is of potatoes turning green.
Watch out for blight, which can be a real problem with non-resistant varieties.
Pumpkins and squash
These plants ramble and the foliage may threaten to swamp other plants. Be ruthless: cut off a few leaves, once fruits are set, and train stems to run where they cause the least problems. Stems can loop around on themselves if necessary. Depending on the variety, there may be three or four pumpkins starting to swell on each plant. Lift fruit carefully and slip a board, tile or slate underneath. This prevents the flesh rotting where it touches against damp soil.
Pumpkins and squash under cover ripen much faster than ones grown outdoors, and they may be ready by the end of the month. Once the fruit has stopped swelling and has reached a good colour, and the skin is firm, harvest each one with an inch of stem attached. Remove the haulms to free up space for other crops. Pumpkins will keep for months in a cool, frost-free shed, but squash is best eaten within a few weeks.
Broccoli
Young plants will be large enough to put out in the border soil in August. Try interplanting with another crop, such as sweetcorn, if space is limited. The corn will provide some shade and you can still harvest cobs while the broccoli is growing. Just be careful not to break the brittle corn stems. Once the corn has finished producing, you can remove the stalks and leave the broccoli to grow on unrestricted.
Plant broccoli plants 45cm/18in apart with 60cm/24in between rows. Add a scattering of lime if the soil is acid, but plants will do well on the nutrients left by the previous crop.
Try sowing calabrese for a fast autumn crop.
Peppers
Sweet peppers should be covered in fruit at several stages. Large green peppers will ripen, to red or orange, if left on the plant. A few varieties ripen to more unusual colours, but it can be part of the fun to see what shades come out of a mixed pepper patch. Picking fruit at the green stage is supposed to allow more flowers to set fruit. However, it makes most sense to pick peppers when the person eating them thinks they taste best – some people hate them green and love them red, others love the green ones. Either way, there should be plenty of fruit for a few months yet. Use string or twigs to provide extra support if necessary. An unsupported limb laden with peppers can snap from the main stem, wasting most of the fruit.
Peppers need a lot of potash, so scatter wood ash, or apply a seaweed-based feed while fruit is swelling on the plants. They also like plenty of sunshine, so don’t grow plants in the shade of tall crops. If light is short, remember the aluminium foil trick mentioned in July. Poor air circulation, low temperatures and lack of sun are the main reasons for peppers failing on the plant.
Chilli peppers are slower to produce fruit than their sweeter relatives. They also need plenty of sun to build up a hot taste. In a sunny position they will produce fiery little monsters until hard frosts kick in. Remember that red chillies tend to be hotter than green ones and that the hotter the growing temperature the hotter the fruit. Always taste a tiny scrap first, to check if a variety is a real scorcher.
Ripening peppers ‘Gypsy’
These can also benefit from an aluminium foil mulch. Just make sure the ground doesn’t dry out too much underneath.
Fruit should be swelling nicely and the first aubergines might be ready for picking this month. Be sure to harvest while the skin is firm and shiny. You will need to watch out for sharp spines on the stem, as these can give a nasty prick. Cut through the stem with a knife or clippers. Don’t just tug on the plant, as roots may be damaged.
August is ‘make or break’ month for this temperamental vegetable. Some people grow aubergines without any problem; other people just can’t seem to get them to work. Poor fruit set can be due to low temperatures, poor feeding or poor pollination (or all three at once). If no fruit has set, dampen a paintbrush and transfer pollen as early in the month as possible.
If we get a hot, late summer, it’s still possible to get late fruit. Feed with a seaweed-based liquid feed and apply well-rotted horse manure as a mulch around the aubergine plants. Keep the soil moist but not soggy. There are no guarantees, but this treatment might do the trick.
Top Tip
Remember to spray water over the leaves every day in hot, dry conditions. This will reduce problems with red spider mite.
Aubergine fruit and flowers
Grape vines
A grape vine in late August is a wonderful sight. Dangling bunches of fruit stretch all along the vine. Black varieties start to darken in colour and all will sweeten up if they get maximum exposure to the sun.
Water around roots, trim any leaves that shade bunches, remove any mouldy grapes and by all means taste a few ripe-looking ones to see when the first bunches are ready to eat. Real sweetness may not kick in until September, but it’s always worth sampling at an early stage.
Grapes starting to ripen
French beans
Climbing French beans do particularly well under cover and can continue to crop for a few weeks yet, but if they are blocking too much light, the end of August might be time to remove them for the sake of other crops. It’s a question of judgement and balancing what is gained with what is lost.
Don’t forget the two rules of polytunnel growing in the summer months
• Water regularly and carefully according to the demands of each crop. Nothing grows well in dry soil. If the atmosphere is very dry, hose down paths and mist overhead for moisture-loving plants.
• Ventilate and allow air to circulate between plants. Doors may well be left open day and night, or at least they should be opened as soon as the sun shines. Overheating can kill plants! Cut back foliage to allow air to move freely. Damp, muggy, overheated conditions can lead to lots of problems with moulds and mildews.
Top Tip
If August is wet and there is nowhere to dry your onion crop, bring the bulbs into the polytunnel. Spread them around in any available space, or hang bunches from the framework. Don’t spray the bulbs with water and don’t leave them more than a couple of weeks. The environment is usually too moist for ongoing storage, but some useful drying can be done while the weather is wet outside.
Enjoy the August harvest
French beans
Grapes
Sweetcorn
Tomatoes
Aubergines
Peppers
Basil
Melons
Cucumbers
Salad leaves
Spinach
Courgettes
Pumpkin and squash
Some harvesting hints
• Regular harvesting is essential in order to keep plants cropping. During holidays ask a neighbour to do the job rather than leave things unpicked.
• Pick everything as it ripens. Look under leaves for lurking monsters and don’t let salad crops bolt.
• Remember to keep nipping the top leaves from basil plants, so that they don’t get a chance to flower.
• Eat sweetcorn over a short period before sugar turns to starch.