The July jungle
The polytunnel can feel a bit like a jungle in July. All those plants that seemed so widely spaced in May are jostling for room and the air can be hot and humid. It’s important to ensure that light and fresh air can reach where they are needed. Keep bulky foliage trimmed and leave doors open so that plants can avail themselves of any cooling breeze. If the weather is hot, try to work under cover in the mornings and evenings, and water at those times too. Spray overhead to cool down any plants that don’t like too much heat and damp down paths to keep air moist.
Weather report
It would be nice to say that July is a glorious month. Indeed it can be lovely, and it can produce beautiful sunny days that record some of the highest temperatures, but July can also live up to its reputation for being the wettest month of the summer. If a series of wet south-westerly depressions sets in, all except the most eastern counties will see a lot of rain. Weather patterns such as this tend to persist once they become established. But it’s not all doom and gloom! High pressure can persist too, so at least part of the month might bring a heat wave.
Patrol the polytunnel every day
Start sowing for autumn and winter crops
Leave doors open
Keep borders free of weeds
Water regularly, damp paths and mist overhead on hot days
Apply liquid feeds
Give a hand with pollination
Peg down strawberry runners
Keep harvesting
Control pests and diseases
Time to sow
Spring cabbage
Swiss chard
Spinach/spinach beet
Pak choi
Kale
Beetroot
Fennel
Kohl rabi
Winter lettuce
Oriental leaves
Parsley
Dwarf French beans
Broccoli
Rocket
Winter purslane
Mizuna
Mibuna
Lamb’s lettuce
Land cress
Turnip
Potatoes
Thoughts on July sowings
• The real test for a polytunnel gardener isn’t how many tomatoes can be grown in a good summer but how full the space is through the autumn, winter and early spring. An unheated polytunnel can be used to grow a wide variety of vegetables through the coldest months of the year, but only if you make sowings (or buy in plug plants) during the summer months.
If you intend to go on holiday in July, and don’t have an enthusiastic garden-minder near by, leave sowings until August. You might get slower autumn crops, but at least seedlings won’t die for want of water while you are away.
• The first sowing of spinach, spring cabbage and a wide range of winter salad leaves can be made in pots or in drills in July. Sow summer varieties of lettuce for autumn crops, but also make the first sowings of winter varieties. Some favourites are ‘Winter Density’, ‘Winter Gem’ and ‘Lattughino’. ‘Valdor’ and ‘All the Year Round’ give softer leaves, but both grow well in a winter polytunnel.
• Ignore the seed packets and try sowing Florence fennel, beetroot and even broccoli. All these give great winter and early spring harvests in a polytunnel.
• Swiss chard – ‘Bright Lights’ or ‘Ruby’ varieties – provides vibrant-coloured stems and tasty leaves. This crop comes into its own in the New Year, when it is good to have colour in a winter vegetable.
• Dwarf French beans sown now will crop through October, or even into November. Sow all these in deep pots and keep them on a bench, near an open door if it is hot.
• Sow parsley in a pot to prick out and transplant later. This sowing will provide pickings right through the winter.
• Try making a sowing of potatoes in containers. These can be started outdoors, but bring them into the polytunnel as soon as foliage pokes through. This reduces the likelihood of blight attack.
Try using sprouted potato tubers left over from a spring planting. These may look shrivelled, but if sprouts are healthy, they can still grow on with surprising vigour once they get their roots into some good compost. Always use a blight-resistant variety like ‘Sarpo Mira’ – this avoids problems with late blight.
The daily patrol
A lot of work in the July polytunnel is based on the philosophy of ‘Take a good look round and see what needs to be done.’ It’s all too easy to focus on one particular job, while not noticing that something else is crying out for attention. Watering can take up a lot of time, but it is possible to use this time to turn a leaf and look for pests, to see if a cucumber is ready for picking, to scatter pollen over sweetcorn or to check for unwanted shoots at the base of tomato plants. Work around the tunnel and take a quick look at each thing. Try to do this regularly: it shouldn’t take long and should be an enjoyable task. This way you can spot potential problems before they develop into serious ones.
Ventilation
You can avoid a lot of problems if you maintain good ventilation throughout the summer months. Moulds proliferate in a stuffy, hot, humid environment and once plants wilt, it is hard to get them back to their former glory. If the sun is up long before you are, it might be wise to leave doors open overnight. If necessary, hang fine-mesh netting across open doors: this will reduce wind chill but still allow some movement of air.
Ventilation is vital in the summer months
Weeding
Plants tend to be a bit overcrowded in a polytunnel and the last thing they need is competition from weeds. Take weeding seriously and it will become less of a chore. If you remove weeds when they are small, and before they seed or spread, numbers will gradually decrease. It’s easy to keep a polytunnel free of weeds. A hoe works fine among widely spaced plants, but do be careful not to damage shallow roots, or put holes in the polythene. Hand weeding isn’t a chore if done regularly. It takes only a short while to work systematically around the beds and pots.
NOTE: Some people swear that leaving the beds covered with weeds helps keep moisture in the soil. This may be true, and it might seem an easy way to operate for a start, but weed problems only get worse if they are left to grow out of control and there will be nothing easy about the resultant mess. Mulch will do a much better job of keeping moisture in the soil without competing for water and nutrients.
Watering technique
Careful watering is essential during the summer months. Plants kept on short water rations will never grow well and in order to survive they will attempt to set seed. It’s always best to water in the evening (or early morning) rather than during the heat of the day. This allows water to soak down into the soil and reduces the amount lost through evaporation. If water restrictions are in place, use water barrels to collect rainwater.
If water is in short supply, try to be economical in its use. Wet around the root area of plants and where nothing is planted leave dry soil. Never flood water on to the top of a mound of soil only to watch it roll away down the sides. Instead make a depression to retain water and pour slowly and steadily, allowing one lot to soak in before adding more. Mulch will always be of benefit, as it keeps moisture in the soil where it is needed.
Plants in pots and containers may need daily watering, although you can avoid having to do this if you stand pots in a tray of water. Plants such as cucumbers and melons should be lightly watered round the base of the stem on a daily basis and sprayed overhead at the same time. Repeat this action several times on hot days and damp down any paths as well. Try to get a balance between the humid conditions preferred by cucumbers and aubergines and the slightly drier air conditions preferred by tomatoes and peppers.
A water reservoir for a tomato plant
Cucumbers
Keep harvesting regularly. There should be bumper crops of cucumbers now. Remove any small, discoloured fruit that doesn’t look as if it will develop. This allows new fruit to set further up the stem. Always pick ripe cucumbers, even if there are too many to eat; if ripe fruits are left unpicked, the plant will stop producing. Give surplus cucumbers away, make pickles or at worst throw them on the compost heap.
Remember to keep adding an extra layer of compost around the base of the stem to maintain healthy root growth.
Cucumbers like a moist atmosphere and they will be more prone to disease, or attack by red spider mite, if grown in a dry environment. Watch out for powdery mildew, which appears as white dots on leaves. The dots can spread until a whole leaf is covered (see Part 5).
Sweetcorn
These really are thirsty plants, so don’t stint on water. Use a hosepipe, if possible, to deliver moisture right to the base of each plant.
Tall stems will grow to above head height and they may end up squashed against the polythene. As long as pollen can still fall freely, this isn’t a problem. Male tassels thrust up from the top of the stem. Pollen drops down from the tassels on to the silks that protrude from the female cobs, which grow in the joint between leaf and stem. Some plants will produce only one cob, others will form two and, in a good summer, a few plants might go as far as three. Good pollination is the key to large, full cobs. In outdoor conditions the wind helps spread pollen, but in the polytunnel it is best to give a helping hand. Shake a few stems in each block of plants to release a shower of pollen. Do this every day until all the cobs are swelling nicely. Incomplete pollination leads to poorly filled cobs. Be gentle: don’t shake too hard, as the stems might break.
If growing more than one variety, try to confine pollen spread to like with like. This can be difficult, but some varieties don’t fill cobs well if they cross-pollinate.
Top Tip
Take care when weeding between sweetcorn plants. The stems are brittle and will snap if bent.
Pumpkins and squash
These grow rapidly and there should be plenty of male and female flowers this month. Pollination of the first flowers can be slow if they are left to their own devices. The best solution is to pick a male flower and strip back the petals, leaving a pollen-laden spike. Pollen can then be introduced directly to female flowers (these have a small pumpkin shape behind them).
If pumpkin foliage is getting out of hand, trim off leaves, or train stems to creep out of an open door.
Top Tip
The beauty of growing pumpkins in a polytunnel is that pollen is early enough, and stays dry enough, to use to set the first fruit. If outdoor pumpkins aren’t pollinating well, simply take a male flower spike from a plant grown in the tunnel and use this to pollinate outdoor flowers.
Basil
Basil will be at its best through July and August. The leaves need to be picked regularly to ensure that more are produced. Nip out any flower spikes, as flowering can make the leaves taste bitter. Harvest carefully so that the plants continue to crop. Pick the whole top cluster of leaves from the end of a shoot; this allows the small shoots that are just appearing in lower joints to grow new clusters. Never strip a plant and don’t pick the lower, large leaves, as these will help to feed the plant for many weeks yet.
Tomatoes
Sun-ripened tomatoes come into their own in July. The earliest are the cherry varieties such as ‘Sungold’, which has orange fruit and must be the sweetest variety going. Fruit at the top of the truss will ripen first. This ripe fruit gives off a gas that speeds up the ripening of fruit lower down the truss. Wait until lower fruit starts to colour slightly, and then pick the ripe fruit from the top.
Low-hanging, long trusses may trail on the ground and fruit can be susceptible to slug damage. If this is a problem, raise them off the ground with twiggy sticks.
Beefsteak varieties are always slower to ripen than cherry ones. Don’t be impatient: these giants of the tomato world will colour up nicely next month. If tomatoes are slow to ripen in a dull year, place a banana or one or two red tomatoes among the green trusses. These will help kick-start the ripening process.
If border soil dries out rapidly, it is worth using a mulch. Using a mulch of comfrey is a great way to provide tomatoes with potash, but mix it with something like grass clippings to give better coverage over bare soil.
Remember to keep feeding with liquid feeds, such as seaweed, every seven to ten days. Once plants have set four trusses, give them a nitrogen-rich feed. This stops plants running thin at the top, helps sustain the growth of many more trusses and ensures that cropping will continue into the autumn.
Keep nipping out side shoots and start removing lower leaves if they are discoloured, badly curled or overshadowing ripening trusses. New shoots will still sprout from the base of the stem. Nip these out in the same way as side shoots, as they draw the energy of the plant away from fruit production.
Harvesting tomatoes
Tomatoes and blight
Keep an eye out for signs of disease (see Part 5). In a damp July, blight will rear its head and it can find its way under cover to blacken tomato leaves. The disease will spread to discolour fruit, but there are a few things that you can do to hold it at bay:
• Keep doors shut, if possible, on damp misty days that favour the spread of blight. Physically excluding spores from the polytunnel is obviously ideal, but don’t risk sweltering crops if temperatures rise too high.
• Remove any blackened or discoloured leaves. These may be a sign of blight or another disease, and it is best to get them out of the way before the problem spreads.
• If blight is a regular problem, grow a blight-resistant variety such as ‘Ferline’.
Climbing French beans
April sowings will start to crop in July. Harvest regularly while the beans are small. Plants need plenty of water to supply such rapid growth, so don’t let the soil dry out; if it does, plants will become more at risk from attack by red spider mite (see Part 5).
French bean flowers
Aubergines
Keep pollinating flowers with a soft paintbrush until four or five fruits are set per plant. Peel away any petals that stick to small fruit: these can be a starting point for grey mould to take hold. Early varieties might start cropping by the end of July.
If plants are in a growbag, remember to start using a liquid feed; the nutrients in the growbag will be exhausted after six to eight weeks of growth. Feed every ten days while fruit is swelling.
Slugs might nibble at growing fruit. This isn’t too much of a problem, since aubergines seem to heal small wounds as they grow; just stop the pests before they make large holes.
Small fruit and flowers on an aubergine plant
Peppers
Plants should be covered in small white flowers. The flowers are self-fertile, although, as mentioned last month, it is worth tapping branches and misting with water if the air is dry. Flowering continues even as fruit starts to swell. This can ensure a long cropping period, with fruit through to the winter.
Sturdy well-grown plants should carry a crop of small peppers by the end of the month. There is no need to limit the number of fruit per plant and some can comfortably produce twenty to thirty peppers over the next few months. Use a liquid feed every week while fruit is swelling. Peppers are part of the same family as tomatoes and they like the same type of feed: high potash but not excessive nitrogen (seaweed is ideal).
Watch out for slugs eating into the heart of developing fruit – peppers will rot if damaged in this way. A few ferric phosphate pellets will stop the problem in an organically approved way.
NOTE: Green peppers are unripe versions of red ones. Pick them green if that’s your preference, or leave them to ripen and change colour on the plant.
Top Tip
Peppers like hot sunny weather. If the month is dull, lay aluminium foil on the ground between plants. This reflects more sunlight on to the plants and helps fruit to ripen; it also keeps the roots warm. But you must remember to water underneath the foil. The same trick can be applied to aubergines.
Melons
Keep pollinating flowers if fruit hasn’t set and twine the stems up strings to keep fruit off the ground. ‘Sweetheart’ melons that set fruit early in June will be ready for eating in July. Fruit should be around 10cm/4in in diameter and should ‘give’ a little if pressed. Ripe melons can smell delectably sweet. If in doubt, leave fruit to ripen for a day or two longer, but never until it rots or falls from the vine.
Larger fruiting varieties will take a few weeks longer to reach maturity. Use nets (the ones from bags of oranges are ideal) to support individual melons, so that the weight doesn’t break stems. Tie the nets on to the framework of the polytunnel or support canes.
Immature fruit on a melon plant
Grapes
Vines are thirsty plants. They shouldn’t really be rooted inside the polytunnel, but if they are, water daily so to make sure that both the vine and nearby plants have enough moisture. If the vine is trained in from outside the tunnel, the roots will need watering in dry weather.
A grape vine can produce a huge number of bunches in a good year. Be brave and remove small and semi-formed bunches (up to half may have to go) so that the remaining ones grow well. Keep removing leaves and prune back side shoots to allow light and air through to the grapes.
Also, it is worth thinning out the smallest grapes from a bunch. Use a pair of small pointed scissors to reach into the bunch and nip out individual stems. This allows the larger grapes to grow well and form a decent bunch. If all the grapes are left to grow on, some will stay small and the bunch can become so tightly packed that few of the grapes will reach their full potential. Thinning is a time-consuming job. Look on it as a meditation: dwell on the fruit that is to come and it may not seem so bad!
NOTE: Thinning individual grapes is a fiddly process, so only bother to do this for dessert varieties. Grapes for wine making don’t need to be thinned in this way.
Swelling grapes
Strawberries
Plants in pots will finish cropping in June or early July. Move them out of the polytunnel, but keep them within the sphere of care. Strawberries produce runners when they finish fruiting and these should be pegged down into small pots. Take runners from the best plants rather than the worst producers, and all should bode well for the next year’s supply. Take only the first plant on each runner – although some will produce two or more, the later ones will be weaker. Once the runner has rooted into a pot of its own, it can be severed from the parent plant.
Top Tip
Although some people say you should discard the parent plant and grow on only the young ones, I always keep the good producers for another year (or even two). If you put sticks in to mark them while fruiting, they should be easy enough to identify. Give the plants a haircut, removing all discoloured leaves and debris from the pot and leaving only the smallest leaves untouched. Two- and three year-old plants in pots can go on to produce superb crops.
Keep picking courgettes for as long as you need them. If you have plenty of these cropping outdoors, it might be time to think about evicting the ones in the polytunnel. If space is in short supply, this might be an essential act. However, if you can spare the space, it’s worth leaving one or two courgette plants to grow on inside the polytunnel. In a bad summer outdoor crops might fail, but the covered ones will guarantee fruit all summer long. In a good summer, polytunnel courgettes might just add to the glut, but they will continue cropping into the autumn long after the outdoor ones are done.
Powdery mildew shows as a white dusting over leaves and is directly connected to overcrowding and dry soil.
Enjoy the July harvest
Tomatoes
Cucumbers
Courgettes
French beans
Salad a-plenty
Basil
Melons
Strawberries
Sweetcorn
Spinach
Some harvesting hints
• The kitchen should be full of produce from the polytunnel. Melons might grace the fruit bowl, along with last strawberries.
• Cucumbers, courgettes and salad can roll in with alarming regularity and it’s hard to keep up with the tomato supply. Don’t be a martyr to excessive production: evict a cucumber plant if there are six of the beasts looking really healthy and producing fresh fruit each day.
• Just a dozen March-sown French bean plants can be producing enough beans to feed a family. Look under the leaves for hidden beans.
• Sweetcorn cobs might start to mature at the end of July. Pick these while young and sweet for some of the tastiest treats.
• Always pick, pick, pick, as this keeps most plants producing. Non-productive plants have no place in this exceptional growing environment.