You can grow sweet corn outdoors in a good summer, but for a more reliable crop you need a greenhouse. April sowings are best done in pots but in May and June seed can be sown directly into its final position. Sow one fresh seed about 1cm deep per tall pot of free-draining compost: if using older seed sow multiple seeds per pot and single the seedlings later with a scissors. Keep the compost warm and not too wet. Sweet corn roots go very deep and do not tolerate confinement, so plant out your crop as soon as possible. Choose the tallest space available, although it won’t matter if the tops are bent over at the roof. Dig large planting holes 30cm apart in a square block to aid pollination. Fill them twice with water and add in some compost when planting; corn needs plenty of water and feeding.
If space is short, you can plant corn between rows of greens due for harvesting soon. Keep watering and feeding. When the sticky tassels appear on the lower female flowers, shake or tap the plants gently each day to shower pollen down from the male flowers above and ensure well-filled cobs. Cross-pollination gives poorly set and less tasty cobs, so if growing different varieties try to plant them as far apart as possible. The cobs mature close together, so sow later crops to extend the season. The cobs are ripe when the tassels darken and wither, and punctured kernels leak milky fluid. They dry up and get starchy very soon, so harvest them promptly, cook then immediately for four minutes in boiling water, and enjoy.
Pollination occurs naturally outdoors, where wind and insects carry pollen from one flower to another to fertilise them and set fruit. Tunnels and glasshouses shelter plants from wind, and fewer insects go inside so natural pollination is sometimes not enough to set a full crop of fruit. Incomplete pollination of a flower can produce a fruit that only develops and grows on one side while the other side remains hard and misshapen. This can be a problem with strawberries. Peaches, nectarines, grapes, melons and aubergines among others can yield better with help.
Hand-pollination is the answer. When the first flowers are just fully open and conditions are dry, brush over the flowers gently with a very soft brush or a little cotton wool. In the past gardeners used rabbits’ tails, but animal welfare was not a consideration then. Paintbrushes are a bit too stiff for pollination, but the likes of a camera lens brush is perfect. Never use one on a lens afterwards, because it picks up oils from pollen that would smear the lens. Pollen grains have spines for gripping onto hairs such as on bees’ bodies, and they brush off onto the sticky stigmata of other flowers – job done. It is best to repeat for a few days running to ensure good pollination and catch the later flowers. Tomatoes are easy to pollinate by vibration; tap on the flower trusses or the supporting canes or wires, or water them from above with a coarse spray of water.
Cold frames are four-sided boxes with transparent covers sloping towards the sun. You can buy readymade ones or easily make your own with new or recycled materials. They are out of fashion nowadays because more people have tunnels or glasshouses, but still very useful.
You can use cold frames to hold plants for which there is no room in your greenhouse just now. They are good for hardening off vegetable plants or half-hardy annuals raised in the greenhouse before planting them out in the garden. You can sow seeds earlier than possible outdoors if greenhouse space is not yet available, or quarantine new plants, or keep plants that need warmer or cooler conditions than you have in the greenhouse. Cold frames are good for rooting cuttings, or warming up water or potting compost before use. If you need an extra degree or two of frost protection for plants inside the greenhouse, you can put a lightweight cold frame over them for the night.
Cold frames are best placed near your greenhouse for convenience, and facing as near south as possible. Their south walls should be low enough to let in the sun. To ventilate, prop open the downwind side of the top cover. If you raise its upwind side, a gust could flip it off, and if you slide it the gap may be on the wrong side letting in chilling draughts. It is harder to control their temperature due to their small volume, so you must anticipate the day’s weather and ventilate accordingly, closing the cover at night. If you expect hard frost, lay a quilt of weighted bubble-wrap or sacks stuffed with leaves over the cover for extra insulation. Water plants in the mornings to let the leaves and soil surface dry off before night.
As the days get shorter and colder, you might think about bringing an electrical power supply to your tunnel or glasshouse. Electricity can power lights, heaters, soil warming cables, propagators and climate controllers, letting you grow a wider range of plants over a longer season. But it’s not just a matter of running an extension cable out from your house; domestic cables and fittings are neither shockproof nor waterproof enough for safety in greenhouses. Electricity and water are a lethal combination. If you only need working lights you could use wireless battery or solar-powered lights with high-efficiency LED bulbs. If you already have a low-voltage garden lighting circuit nearby you could take a short spur off it, provided it can handle the extra load.
If you need mains power, you must get a registered electrical contractor to do the specialised wiring work. At the least, the supply from the house should be through Steel Wire Armoured (SWA) cable buried at least 50-60 centimetres underground with warning tape above it. It should pass through a Residual Current Device (RCD), which monitors the flow of current out from the distribution board and back and trips instantly if they are not the same (i.e. current shorting elsewhere). All sockets, plugs and fittings should be of heavy-duty industrial type with a much higher Index of Protection (IP) rating than domestic ones. They are not cheap, but neither is human life!
We associate mangetout peas with early summer, but you can harvest them from April onwards if you sow them now. They are surprisingly hardy. Sow about four seeds of ‘Oregon Sugar Pod’ or any other variety in four-inch (10 cm) pots of good compost and place them in your tunnel or glasshouse. Protect them from mice until they germinate, and from slugs thereafter. Don’t water them too heavily, and keep them covered with bubble-wrap or fleece at nights to speed up germination. Plant them into a composted trench in the border soil when the plants are about 3” (8 cm) tall. Push in short pea-sticks on either side of the row to support the plants and keep their growing tips off the soil surface, where slugs would eat them. Ventilate well during the day to reduce mildew infections. Cover over the rows at night with fleece or bubble-wrap to protect them on very cold nights. Add in longer pea-sticks if the plants need them. The plants should be ready to flower by April, and generous watering and some feed will help boost yield. Harvest the pods often to keep the plants flowering. You can sow a second, later crop to extend cropping until the outdoor crop comes in. Enjoy!
Mibuna is a traditional Japanese green crop, ideal for greenhouses in winter. Like mizuna, it is a member of the cabbage family and produces green leaves for salads and cooking over a long period. It is grown in much the same way. It is less hardy and productive than mizuna, but its narrow strap-like leaves (often with a white midrib) have a more spicy flavour that gardeners enjoy and some slugs don’t (though some like it hot). It can be harvested as whole plants, but excels as a cut-and-come-again crop.
Seed sown now in containers or borders can produce leaves from October to April or May next. Add in plenty of compost, and sow seed thinly in drills 1cm deep. Border rows should be about 30cm apart. Keep the soil moist: dryness encourages bolting, especially in spring-sown crops. Watch out for flea beetles and slugs. Cut off and compost overgrown leaves and any flowering stems that appear; it diverts the plant’s energy into growing more fresh leaves. Use leaves while they are still young. Eat them raw in salads or lightly steamed or pickled.
Image courtesy of GIY
This summer’s drought may make vegetables scarce and expensive until next year. Plan now to maximise the cropping potential of your tunnel or glasshouse and to leave no square metre unproductive over the winter. It is too late to sow spring cabbage seed outdoors for planting out in the autumn, but raising plants in your greenhouse now may bring on seedlings faster and have them big enough to plant out on time. If you do, harden them off before planting out and protect them from hungry pigeons. Alternatively, plant them in the greenhouse for an earlier crop. Plant single seed potatoes in large pots now, and they should still have time to mature before midwinter. Beetroot, white turnips and kohl rabi will produce small but tasty roots, and you can eat their young leaves too. Rocket, oriental greens such as Pak Choi, kale, winter lettuce, corn salad, Texel greens and winter purslane can be sown in succession for salads. Calabrese, French beans and Florence fennel can all yield well in greenhouses from August sowings if the early winter is not too cold.
If your greenhouse is full already, bring on seedlings in cell-trays and then small pots until planting room becomes available. You can sow radishes, baby leaf greens and other short-term crops between rows of slower growing crops, as they will be harvested before the space is needed. You can still have your five a day!
At the recent Bloom Show we premiered our new roll up side ventilation system which can be fitted to our full range of Garden and Professional Polytunnels. This simple system provides an economical solution for roll up sides and can be fitted to one or both sides of the Polytunnel. A rainwater collection gutter is available as an optional extra feature. We will have this fitted to one of our Polytunnels in our display area this summer.
Side vent winder
New aluminium rainwater collection gutter
New Polydome Roll up side ventilation system
Sweet potatoes are related to morning glory and not ordinary potatoes. It’s possible and fun to grow your own. Plants are usually raised from ‘slips’ taken from sprouting tubers. You can sometimes buy them online or in a garden centre; ‘Beauregarde’ and ‘Georgia Jet’ (with orange flesh) and ‘T65’ (white flesh) are suitable varieties. ‘O’Henry’ produces tubers close to its base and is good for container growing.
Bought tubers can be from varieties less suitable for Irish conditions, but you can still get a small crop from their shoots. Organic tubers unsprayed with sprout inhibitor are best. Stand the tubers half-submerged in lukewarm water with their narrow ends down. Place them in a warm sunny spot to sprout, changing the water daily. Cut off the sprouts when they are about 15cm long. If still rootless, root them in warm water or cutting compost and plant when rooted. Soak bought-in slips overnight in lukewarm water before planting.
Plant them deeply (to encourage tubers to form at the nodes) in light, well-drained, fertile, neutral or acid soil in full sun. Always keep plants and tubers above 10°C/50°F. Give warmed water when needed, and feed weekly with tomato feed. Tie up the sprawling stems or they will root into the ground at the nodes. Green leaves can be eaten in salads or lightly cooked like spinach, but don’t take too many or you will reduce the tuber crop. Dig up the tubers after 3-4 months when the foliage turns yellow and dies back. Avoid damaging them as they bruise easily. Dry the roots in the sun for a few hours and then cure them for five days at 30-32°C / 85-90°F and 85-90% humidity. Store them above 10°C/50°F in good ventilation and either eat them soon or blanch and freeze them.
The Polydome Display Area with most snow removed from roofs in advance of the promised blizzard.
As the whole country is bracing itself for the ‘Beast from the East’ we would like to advise customers with Polytunnels and Glasshouses that once it is safe to venture outside you should remove snow as it is surprisingly heavy and can collapse structures if allowed to build up excessively.
If you have an electric heater for use in Greenhouses (specially sealed for a wet environment) you could leave it running as the warmth may help to melt snow before it has a chance to build up. If you have a direct fired heater – e.g. a gas heater that works like a gas hob inside a metal cover, only leave it running if you can be positive that there is a fresh air supply to it that will not get blocked (otherwise it will burn up all the oxygen and produce carbon monoxide with potential disastrous consequences).
Any number of ways (such as soft bristled brushes, sheets, mop handles etc.) can be used to dislodge snow but whatever you choose try not to damage your polythene or glass in the process, so use something soft so that it will not scratch (causing reduced light transmission) or tear the cover or break the glass.
It is also possible to prop the roof inside your Greenhouse or Polytunnel, but of course this should be done before snow builds on your structure in case it could collapse while you are in there.
We hope that everyone will be safe and well which is the most important thing, your Greenhouse or Polytunnel can always be replaced – and you may even have insurance to cover it, but of course it is not worth taking any risks to protect it.