June polytunnel
Things can get very hot in the June polytunnel. The cold nights are gone (in all except an extraordinary year) and tender plants start growing with a vengeance. Plants need to make a heavy crop in the next few months and you need to do everything possible to encourage strong, steady growth. Young tomatoes, melons and cucumbers will flourish with the extra heat, provided they are supplied with water and given an occasional feed, and doors are opened to let a warm breeze drift through.
Weather report
June can be the hottest, sunniest month of the year. It can also be the driest. There is little chance of gales, and daylight hours are long. If high pressure sets in it can stay for weeks, but in some years the heat can be late to arrive and in others a cold wet airflow seems to persist. Whatever the weather throws at us, the polytunnel is a sheltered space. This might mean that it gets too hot on bright sunny days, so plan any work for mornings and evenings. On bad days, enjoy the shelter and work in the polytunnel at any time of the day.
June jobs in brief
Water carefully and ventilate to create a healthy growing environment
Mulch to keep moisture in the ground
Make a few sowings
Mist tomatoes and nip out side shoots
Plant out melons, peppers and aubergines
Thin grapes
Tie large plants into supports
Remove any diseased foliage
Feed growing plants, especially in pots and growbags
Pick lots of early summer crops
Watch out for pests and diseases
Time to sow
Lettuce
Salad leaves
Sweetcorn
Spinach
Florence fennel
Cucumber
Kohl rabi
Parsley
French beans
Broccoli
Kale
Beetroot
Grow summer lettuce in the shade of tall plants
Thoughts on June sowings
• Although the polytunnel should be bursting with lush summer growth, now is the time to start thinking about autumn and winter crops. Most sowings for these can be made in July and August and it isn’t essential to sow in June. However, it makes sense to locate seed of spring cabbage, Swiss chard, kohl rabi, winter lettuce, pak choi, Florence fennel, mizuna, mibuna, corn salad, oriental greens, etc., so that they are all ready to sow next month. And there are still some seeds you can start this month in order to keep one step ahead.
• Lettuce and salad leaves should be sown every four weeks throughout the summer to give a constant supply.
If you want to grow successful lettuces in a polytunnel through the summer months, grow them in the shade created by tall-growing plants.
• Try sowing sweetcorn in June rather than miss out on the crop. In a poor summer these plants may not reach best expectations, but in an Indian summer they can achieve a reasonable harvest of full cobs. Sow two seeds per station, directly into the border. Sow in blocks, allowing 30cm/12in between each sowing point. Remove the weakest seedling to allow the strongest one in each couple to grow on. This gives late sowings the best chance.
• Florence fennel, sown at the end of the month, will grow a healthy crop for late autumn and early winter. Sow seed thinly in deep pots or trays.
• Cucumbers can be sown in early June. These will grow fast to give a late crop. If this is the only option, it is worth a try.
• Many overwintered brassicas do really well under cover: they give earlier and cleaner crops than those grown outside. The problem is that the polytunnel is usually bursting at the seams with summer crops and no one is going to make space for slow-growing winter greens. These can be sown later than greens for outdoor crops (June sowings of sprouting broccoli and kale can be very successful), but an alternative is to buy in a few plants and keep these in large pots outside the tunnel door. These can go into the polytunnel when space clears. These plants may seem smaller than ones from the same sowing that are planted in an outdoor bed, but don’t worry. They will soon catch up and overtake outdoor plants, and will even crop a few weeks earlier.
• If there is space in the polytunnel, it is worth making a second sowing of dwarf French beans in June. These can be sown directly into the ground in a double row (rows 20cm/8in apart with 15cm/6in between plants), or in pots to be planted out in a few weeks’ time. June sowings can crop really well, even in a poor summer, and should give good pickings into the autumn.
• Climbing French beans can still be sown at the beginning of June. Sow in situ, 20cm/8in apart in a trench filled with moisture-retaining compost. Beans like plenty of water, so anything that will help keep moisture in the soil is a bonus.
• Basil can still be sown in early June, but it is much better to buy a pot of young plants from the supermarket (look in the fruit and veg section). Choose short, strong plants and split these into large pots in clumps of three or four. Soak the root ball before planting.
• Sow kohl rabi in late June for autumn crops. Sow thinly in pots and transplant out as space clears. This crop can even be dotted around among others if space is tight.
• Beetroot can be started in cells for a winter crop. Seedlings won’t take any harm from being transplanted in a few weeks’ time.
Dwarf French beans
Tomatoes: flowers, fruit and side shoots
Spray early tomato flowers with a mist of water to ensure the first fruit set. This isn’t necessary with later flowers, but those in early June will certainly benefit. Larger tomatoes will usually flower a few weeks behind the cherry ones and beefsteak varieties may only start flowering in June. The lower trusses of cherry varieties should be filling up with green fruit and there may even be some ripe tomatoes before the month is out.
Ripening at this point in the year depends on sunshine levels, but once some tomatoes ripen, they will give off a gas to stimulate other fruit close by to do the same. For this reason I never strip all red fruit off the first ripening truss.
If lower leaves overshadow trusses, remove a few to allow light in. There should be plenty of leaves growing further up the stem to feed the plant.
Keep nipping side shoots out of the joints between leaf and stem on all except bush tomatoes. If left to grow, the plant will put more energy into growing leaf and shoot than into fruit. Side shoots spring up from around the base of the plant as well as where the leaves meet the stem. Check, check and check again – it’s amazing how more always seem to appear.
If the main shoot is damaged or weakened in any way, you can grow a strong side shoot on as a replacement and nip the main shoot out.
Fruit starts to set from the top of a tomato truss
Keep removing side shoots
Tomatoes: support, water and feed
Tomato plants grow tall and need plenty of support, so remember to tie the main stem in to a pole, cane or string. Ties every 15–20cm/6–8in do a good job. If using thin string, wind it around a few times, so that it doesn’t cut or break the stem. Always allow enough slack for the stem to thicken as the plant grows.
Correct watering can be the key to productive plants. The aim is to encourage roots to go as deep as possible and hence plants will be more able to survive through the summer months. Water tomato plants really thoroughly every couple of days, soaking the soil well. Tomatoes need lots of water, but they hate sitting in soggy soil day after day. Wait until the soil’s surface has dried out before watering again. It is best to water in the evening or early morning, as this gives a chance for moisture to soak down into the soil and less is lost through evaporation. Tomatoes in pots and growbags will need a good soaking every day. This may even need to be done twice a day in really hot weather. Tap the side of a pot with a stick if unsure: pots sound hollow when the compost is dry.
Tomato plants always benefit from a potash-rich liquid feed. Many tomato feeds are based on seaweed. Either buy in a concentrated organic one or make a brew (see Part 7). Both should be diluted before use. For the non-squeamish, urine makes an excellent liquid feed for tomatoes. Dilute the contents of the chamber pot with twice the amount of water before pouring around plants. Apply a feed every seven to ten days while fruit is swelling. Feed plants in containers every seven days. Diluted liquid feeds can be poured into the bottle watering system (see Laying out the inside of the polytunnel), or over the surface of the soil.
For a ‘quick hit’ spray the leaves with a fine mist of seaweed feed. Take care: nozzles will block and sprayers won’t work if there are any lumps of organic material floating in the liquid feed. If necessary, flick the liquid over the leaves with a soft brush.
One red tomato helps others to ripen
Tomatoes: disease
Watch out for signs of disease (see Part 5) and remove any affected leaves, or squash pests before the problem spreads.
• Moulds, mineral shortage and virus disease can discolour leaves and stems.
• Whitefly might take up residence on the lower sides of tomato leaves.
• Blight can strike in June, although tomatoes grown under cover can be kept free from spores by keeping doors closed on the dull, humid days that favour the spread of this disease.
Cucumbers
Plants sown in early March should be cropping abundantly. A healthy cucumber plant can produce between twenty and fifty fruits in a season. Some fruits may be less than perfect in appearance, but they will taste just as good. Keep picking to ensure that more grow. Plants should have fruits at all stages of development at any one time. If large cucumbers are left to mature and ripen seed, the plant will think it has achieved its mission and will stop producing young fruit.
If the variety isn’t an all-female one, check to see if male flowers should be nipped out. This prevents pollination of female flowers and hence avoids the problem of bitter fruit. Recheck the seed packet: it will tell you if nipping is needed or not.
Keep twirling stems around strings, or tying them in to sticks, to provide support. Once the stem reaches the roof, let it trail back down again, but make sure that the stem doesn’t make too acute a turn, as otherwise it might snap at the highest point.
Cucumbers need careful watering. In fact, they do best with that peculiar mix of a free-draining yet damp root run. Make sure the compost is damp, but never too wet. This may mean watering twice a day to keep up with the demands of these thirsty plants. Give cucumbers a spray over the leaves – they enjoy a humid climate and may find the polytunnel too dry at times.
Cucumbers do well if fresh compost is piled up around the lower parts of the stem. Do this every couple of weeks. New roots will soon grow from the buried part of the stem. This helps overcome problems with root rot.
One cucumber plant can provide lots of fruit
Other cucumber problems
Add a teaspoonful of Epsom salts to the watering can if leaves show signs of magnesium deficiency – older leaves turning yellow between dark green veins.
If the soil is too dry, powdery mildew might show as white splashes of mould on the leaves. Alter the watering regime and use a milk spray to combat this disease. Red spider mite can be a problem in dry conditions; to avoid it, keep foliage damp.
For more on pests and diseases, see Part 5.
NOTE: Cucumbers are sensitive plants and you may do more harm than good by using a bug spray. Even ones based on derris or pyrethrum can do harm.
Peppers, aubergines and melons: planting out
These are some of the most tender crops and little is lost by waiting until early June to plant them out. In fact, all these will suffer if they are put out in an unheated structure where night-time temperatures drop below 12˚C/54˚F. Choose plants with strong stems and plenty of leaf. If leaves are curled they might have greenfly hiding in the folds.
Slow and steady growth is the aim (for soil and planting techniques, see May). Tall plants will need support, so provide stakes and tie in stems. This will help the plants support a heavy crop. First flowers should appear in June. These will be self-fertile and won’t need much help with pollination, but to ensure an early set, lightly mist with tepid water and tap the flowering stems gently. Peppers need plenty of water. The flowers tend to drop off if roots are dry, or if humidity is low.
Pepper flower
Aubergines
It may still be necessary to cover young aubergine plants with an extra covering. This can provide an essential bit of extra warmth. Ideally, aubergines should be kept away from draughts, so don’t plant them near the polytunnel door.
I use a propagator frame (once it has finished the job of raising small plants) as a large cloche to cover aubergine plants.
Aubergine plants will start to produce lovely purple flowers towards the middle of the month. These may need a hand with pollination. Transfer pollen with a soft paintbrush. Dampen the bristles by running the brush across your tongue – no more, as it will be too wet. Successfully pollinated flowers set marble-sized fruit behind the petals. If petals stick to this, peel them off. If flowers aren’t successfully pollinated they shrivel and drop off the plant. Don’t worry if this happens – more flowers will grow – but the best fruit is often grown from the earliest set.
Aubergines need careful watering. If the weather is dull and damp, don’t spray any water over the leaves. However, in a hot dry spell it is essential to spray the leaves in order to ensure fruit set. Spraying with water will also help to keep red spider mite under control. Aubergines are particularly susceptible to this pest.
Pollinating an aubergine flower
Debate on aubergines
Some people advocate nipping out the tops of aubergine plants when they reach 20cm/8in high. This forces them to produce a more bushy plant. I never do this and I’ll tell you why. It’s hard enough to get a good crop of aubergines in an average summer. In a bad summer it can be almost impossible. Anything that defers the crop (even though it might mean you get more fruit in a good, long, hot summer) can mean a delay to first fruits. Where I live, quite high above sea level, the first flowers are the ones most likely to make successful fruit. If I delay first flowers, I might get more of them, but too late to produce good aubergines. If you live in a warmer area, however, try nipping the top of one plant and see how it does. It may be that the technique suits you better than it suits me.
March-sown plants can open the first flowers by the end of May or early June. Female flowers have small melon-shaped swellings behind them, whereas males are borne on a thin straight stem. The female flowers won’t set fruit unless they are fertilized. Break off a male flower and introduce pollen manually to make sure this happens. The usual advice is to wait until there are four female flowers open on the same day, pulling off single flowers before that, to ensure that four melons grow on each plant rather than one singleton. This is all well and good, but don’t wait weeks for the hallowed day and leave the whole thing too late – two or three melons are better than none!
Melons can be left to ramble over the ground, but this is really a waste of space when they are growing in a small polytunnel. Use strings tied in to the framework to support growing plants. Simply twirl the growing stems around the string; tendrils will then twist around to provide a firmer grip. Growth can be very rapid at this time of year, so don’t leave lengths of unsupported stem to flop and break.
Melons do particularly well in growbags, but it is always worth making a few drainage holes in the bottom and sitting the bag on a layer of compost to facilitate wandering roots.
Twist melon stems around support strings
Sweetcorn
If you put plants in the ground last month, stems can be 60cm/24in tall in June. Sweetcorn is a really greedy plant. If growth starts to slow, give it a liquid feed; otherwise let plants reach for the sky on the stock of nutrients dug in at planting time. Water regularly to optimize the number of cobs per stalk.
Sweetcorn should be planted 30cm/12in apart in blocks to aid pollination (for planting techniques, see May).
Some sweetcorn varieties mustn’t be allowed to cross-pollinate with other varieties. This is especially true of the supersweet varieties, which will lose some of their sweetness. However, I have successfully grown two varieties at opposite ends of a 10m/33ft polytunnel without any obvious loss of taste. Without wind to carry the pollen, most of this will fall close to where it was produced.
French beans
If you sowed beans in pots last month, plant them out now (for planting technique, see April and May). Think about where to position climbing beans, as they can form an effective curtain that restricts sunlight to anything it overshadows. This can be a bonus for salad crops, which don’t fare so well in the full summer glare. Alternatively, grow climbing beans on a north wall, or in a north–south alignment so that all sides get some sun.
March- and April-sown dwarf beans should be cropping well in June. Pick the pods when small and the plants will continue to produce bountiful crops for several weeks. Remember that all legumes need plenty of water when they are in flower. Make sure water isn’t just shed by the leaves: get the hose underneath to make sure soil is wet around the roots.
Climbing French varieties grow rapidly and will twine around a support string once they have found it. Just give a nudge in the right direction when the young shoots first start to seek a support.
Red spider mite loves French beans and can get out of control in a dry environment (see Part 5). Leaves turn a reddish brown colour and small mites can often be seen on the underside. Spray water over and under leaves to reduce the severity of the attack.
Grape vines
Check over established grape vines. There should be small bunches of embryo fruit at the beginning of June. By the end of the month this will have started to swell. If you haven’t mulched the vine with manure, use a nitrogen-rich liquid feed around the roots – anything to get nutrients to the growing crop. Remember to water around the base of the vine. If this is planted outdoors and trained round to grow into the tunnel, it can be easy to forget to water in dry weather, but it is essential to do so if your aim is to grow a good crop of grapes.
Pruning a grape vine
Pruning grape vines
There is an art to producing an immaculate vine full of perfect fruit, but don’t get so intimidated about pruning that you avoid the task altogether. The vine may not look so amazing as one that is perfectly cropped and trained, but a basic pruning job will still lead to plenty of grapes.
1. Any lateral shoot that has formed two embryo bunches should be stopped by cutting out the growing point. Cut this after the first or second leaf beyond the fruit. Choose whether to cut after one or two leaves on the basis of how much shade the vine casts.
2. Stop non-fruiting lateral shoots after they have grown two or three leaves.
3. Don’t prune the main stem, but do tie it in and support any new growth, so that the vine doesn’t break under the weight of a heavy crop.
Pruning new vines
Leave two main shoots to grow on and cut side shoots after they have grown five leaves. Choose the strongest of the two as a leader next year. Pick off any bunches of embryo fruit that form in the first year.
Basil
This glorious herb will be ready for picking at just about the time tomatoes start to ripen – a perfect taste combination! Pinch out the top cluster of leaves on each shoot before a flower spike appears. New clusters will grow from the small leaves lower down the stem. Nip off any flower spikes that start to grow. Flowering affects the flavour of the leaves, so nip the tops regularly to keep basil at its best.
Picking basil
Plants will still be cropping well in their pots in the polytunnel. Keep them watered and fed while fruits are swelling. Harvest ripe fruits before slugs or birds eat them and remove any fruit that shows signs of grey mould (see Part 5). Move pots out of the tunnel as soon as they stop being productive, to make room for other plants.
Top Tip
Put a stick in the pots that have the most productive plants. These are the ones you will want to use to propagate new plants for next year. Once you have picked the berries it can be hard to remember which plants cropped best.
Plenty of strawberries
Holiday time?
June can be a relatively easy month in the polytunnel. Admittedly, there are growing plants that need ongoing care and attention, but most of these will be planted out and growing well. The autumn and winter sowings don’t need to be made for another few weeks. In fact, if you are planning a summer holiday, the end of June is about as good as it gets in terms of not leaving too much responsibility for seedlings, or excessive harvesting duties, in other hands.
Top Tip
If you are going away, sink pots of seedlings into the border soil. You can lift these when you return, but in the meantime the roots will keep at a more even temperature.
Ventilation and watering
Fine-tune ventilation by opening one door or two, depending on the day. Remember that you can prop doors so that they stay just ajar, or fling them fully open to catch any puff of air. Of course, if it is cold and wet, doors should still be closed at night to keep in any warmth. Avoid hot and humid conditions, which favour the spread of disease.
Water regularly and don’t let anything dry out completely. Spray overhead to reduce problems with red spider mite and dampen paths to keep humidity up. Remember that cucumbers prefer a higher humidity and will always benefit from a spray of water over the leaves. Tomatoes and aubergines like their leaves to be a little drier, but try to wet the soil thoroughly around the roots every couple of days. Pay special attention to the needs of growbags and containers.
Mulch
Always wet the soil well before covering it with mulch. Lots of readily available materials can be used to cover the ground: black polythene, cardboard, grass clippings, cocoa shell, bark chips, mulch matting, cut comfrey leaves, etc. Admittedly, there are problems with some of these: polythene can make a good hiding place for slugs; comfrey rots down rapidly and so doesn’t cover the soil for long, although it does provide tomatoes with potash; and grass clippings must be free from seeds. However, if water is in short supply, it’s wise to look at mulch as a way of reducing evaporation.
Mulch is particularly useful if you are going away on holiday, as it can reduce the number of errors that an enthusiastic neighbour might bring to bear.
Courgettes
Cucumbers
Tomatoes
French beans
Salad leaves
Lettuce
Basil
Kohl rabi
Potatoes
Carrots
Mangetout peas
Broad beans
Some harvesting hints
• There should be plenty of tasty treats this month. As usual the key is to keep harvesting in order to keep plants producing. Eat things while they are small! That’s the joy of June. The freshest tastiest crops are pouring in. There will be plenty more to follow, so leave nothing to grow too large and tough.
• There should be lots of salad leaves. These can, of course, grow outdoors, but the polytunnel ones come faster and are more likely to be blemish free.
• Cucumbers, kohl rabi, fingerling carrots, tiny courgettes, slim French beans, strawberries and the first cherry tomatoes, basil for pesto . . . Summer has certainly arrived and the picking is easy as can be!