Garlic has many health benefits, and growing our own is easy when you know how. Homegrown garlic has only the chemicals you apply, and you can eat the leaves and flower-stems when they are young. Planting garlic in a tunnel or glasshouse now can give you bigger and earlier bulbs than outdoor crops, but even starting a crop in modules or pots under cover and planting it out later gives some benefit. It stops the birds pulling them up too.
The ideal soil for garlic is light, well drained, moderately fertile and neutral or alkaline. Wet sticky clay can rot the bulbs and very rich soil encourages leafy growth at the expense of the bulbs. A good supply of potash helps, so dig in some wood ashes before planting. Garlic needs a long, cool growing season and a cold spell to stimulate maturity, so autumn planting is ideal. However, you need to choose your material carefully.
Do not plant shop-bought garlic and expect a decent crop; you may be lucky but it is sold for eating rather than planting and may be treated to inhibit growth, or carry plant diseases that will persist in your soil for many years. Get disease-free sets of varieties suitable for autumn planting from a garden shop or centre. Gently split them into cloves, and plant the bigger ones 2-5cm deep into the soil 15cm apart, in rows about 30cm apart, with the pointy end up and the flat base down. Plant the small cloves close together to produce leaves like chives. Water the crop lightly and let it dry out between waterings to prevent rotting. Dig up the bulbs gently when harvesting, and avoid pulling them. They bruise easily and then will not keep. Dry and store them in a cool, airy place.
Mizuna is one of the oriental greens that Europeans should grow and eat more. It’s best grown rather than bought because it needs to be eaten right after harvesting for maximum flavour and nutrient value, though it will keep for a couple of days in the fridge. Like lettuce, you can sow seed little and often all year round in a glasshouse or tunnel. September sowings will produce deeply cut leaves up to April or May: single leaves can be cut off after about three weeks and whole heads after six to eight weeks.
Mizuna likes moist rich soil, so dig in plenty of compost or other organic matter before sowing. Sow the seed about a centimetre (half an inch) deep in drills about 30cm (12 inches) apart. Protect the seedlings from slugs. Keep it well watered and ventilate on sunny days – it is prone to bolting in hot dry conditions. If it does bolt remove the flowering stems right away to keep it leafy and sow another batch to replace it. Don’t worry if it wilts after a frosty night: it is hardy and usually recovers. It is a member of the cabbage / brassica / crucifer family so don’t sow it in the same ground as any of its relatives for at least three years to prevent disease build-up
Mizuna has a milder flavour than either mibuna or rocket, and is good in mixed salads. Like spinach it can be steamed, boiled or stir-fried but it shrinks a lot, so harvest plenty. ‘Kyoto’ is a good variety to try.
Basil is easy to buy from the shops, but you can grow a wider range of types yourself at lower cost to you and the environment. The type sold in non-returnable pots is usually sweet basil suitable for salads and pesto, but there are also cinnamon and lemon basil, varieties with purple leaves that look great in green salads and spicy or liquorice-flavoured Thai varieties that combine well with Asian food.
Basil is a fast-growing, tender annual that needs lots of light, heat and water. Being very sensitive to cold, it is an ideal candidate for tunnels and glasshouses, especially in our unpredictable summers. It improves the flavour of tomatoes when served with them, and some say that it also does so when grown with them. It grows best in well-drained acid or neutral soil. Sow a succession of crops, but just a couple of plants each time is enough for regular use unless you want extra for pesto. Either sow them in cell-trays or in situ in the greenhouse soil, thinning them to single plants as soon as they are big enough to see. Use a scissors to avoid root disturbance. Thin or place the plants to about 30 centimetres apart. Harvest leaves as soon as the plants are about 20 cm tall, by cutting off shoot tips. Leave on the lower leaves until you discard the plant; they will produce the food to grow new shoots from the lower side-buds. Even if you need no basil, cut off the tips to prevent flowering (which makes the leaves bitter) and encourage fresh sprouts to grow. Surplus leaves can be either frozen for later use or composted, and the flower-buds are edible too.
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!