Undercover: February 2011
By: Web Editor
Growing in a polytunnel or greenhouse? Sue Stickland has all the information you need to help you get the best from your protected space.
February brings the tipping point between winter and early spring – when the days become long enough and the sun strong enough to see plants undercover start to grow. It means serious sowing and planting can begin.
Sow and plant
Sow in pots or modules for planting out undercover: Tomatoes*, peppers*, chillies*, aubergines*, spring onions*, lettuce, kohl rabi, calabrese, sugar peas, summer cabbage, spring onions*
Sow in pots or modules for planting on veg plot: Onions*, broad beans, early peas, celery*, celeriac*
Sow direct undercover: Radish, sugar peas, annual spinach, cutting salads (leaf lettuce, rocket, cress, oriental greens), carrots
Plant undercover: Early potatoes
(*seeds which need extra heat to germinate)
Winter salads (chicories, Oriental greens, lambs lettuce, claytonia, spring onions), spinach, chard, spring onions, parsley
A colourful harvest
The cold weather has one advantage at least – it deepens the red/purple colour in overwintered leafy crops, so homegrown salads can look stunning. As well as red chicories, there are purple mizunas, purple pak chois and both plain and feathery red mustards (‘Giant Red’ and ‘Red Frills’). If you haven’t grown any of these this year, add a few to your sowing list for the autumn.
Don’t be in a hurry to pull up any overwintering leafy crops, even if they look scrappy. Instead, remove diseased and yellowing leaves, and weed between plants while you have chance. They have had time to make strong root systems and should put on plenty of growth before bolting – much more than their spring sown counterparts – to give you several more weeks of harvesting.
Warmth makes all the difference to seed germination, so make the most of any heated space. The tender crops which benefit most from early sowing are the slow-growing ones such as peppers, chillies and aubergines. Tomatoes can wait until the beginning of next month if necessary.
Large seeds such as peas can be ‘pregerminated’ indoors. Spread them thinly on moist paper towels in a flat plastic container, and put them in a warm place (around 18-20C/65-68F) – an airing cupboard is ideal. Check daily to make sure they are still moist. Once the tiny white roots start to emerge, sow them carefully in pots or the polytunnel border.
Remember that if you sow tender crops now, the seedlings will continue to need extra heat and good light to grow on. If you have no heat in your greenhouse or tunnel, a warm windowsill can accommodate a few but lack of all round light gives straggly plants. One possible solution is to put a grow light (one that mimics natural sunlight) over plant trays in a warm room (suppliers such as Two Wests & Elliot www.twowests.co.uk or Harrod Horticultural www.harrodhorticultural.com have ones that are easy to set up).
Dig in green manures
Continue to prepare polytunnel and greenhouse beds, as the time for early summer planting is approaching fast. Green manures should be left to decompose for at least three weeks before any following crops are planted and longer if you are sowing direct. Undercover, this usually means digging them in during February or March. Cut off the foliage with shears first to make it easier. Water the prepared beds if they are dry, and cover them with polythene to keep in the moisture; clear polythene will also help to warm the soil.
Water and ventilation
Once growth starts, so will the need for regular watering. If in doubt, push your fingers into the soil to see how wet it is beneath surface. Temperatures can rocket in the stronger sunshine this month too, so open doors and vents fully on warm bright days. Good air circulation helps prevent fungal diseases.
Plant early potatoes, spacing them 30-40cm (12-15in) apart each way. I usually cover the bed with a plastic sheet after planting to give them extra warmth, and leave it on until the shoots emerge. Alternatively plant in large pots, allowing one seed tuber per 20 litre pot.
...and sweet potatoes
Tubers of homegrown sweet potatoes kept overwinter can be coaxed into growth at the end of the month to provide shoots or ‘slips’ for propagation. Plant them just below the surface in pots of moist well-drained gritty compost, and put them somewhere hot indoors (20-30C/68-86F) – near a boiler or radiator, for example. Otherwise you can order slips through the post (eg from Thompson & Morgan www.thompson-morgan.com) for April/May delivery. Shop-bought tubers will sometimes also sprout, but they may not be a type that grows well in the UK and could carry disease.
Moles and voles
The problem pests at this time of year are not usually the small insects but the large pests such as mice, voles and moles. Mice and voles are infamous for eating pea and bean seeds but they are also surprisingly fond of greens. They will cleanly nibble out the tender tasty hearts of spring cabbage or parsley, for example. Keep a close watch, because the damage isn’t always easy to spot at first. As an alternative to trapping, I find putting Environmesh over the plants and tucking it well into the soil at the edges will keep these small rodents out.
Moles appreciate the warmer soils and ready source of worms undercover in early spring, and their tunneling can raise and crack the soil – enough to either bury seedlings or leave their roots high and dry. Various devices are reputed to deter these pests, from traditional mothballs to ultrasonic buzzers, and might be worth a try in the confined area of tunnel or greenhouse. Instead I usually rely on vigilantly firming the soil and watering around disturbed plants.
Undercover fruit crops
Plant any fruit trees or vines undercover before the end of this month if possible. In a traditional vine house, the vines are planted outside and the main stem (or ‘rod’) led inside through a hole in the brick wall – the roots can then take advantage of natural rainfall. If you are mimicking this in a modern greenhouse or polytunnel, avoid waterlogging by making sure that rain running from the roof is channeled away. Otherwise plant directly inside, and mulch to conserve water.
Hand pollinate the flowers of peaches and nectarines that bloom this month, as few pollinating insects will be around. Transfer the pollen from flower to flower every couple of days using a soft paintbrush.
• Prepare beds with compost or well-rotted manure
• Dig in overwintering green manures
• Tidy, weed and water overwintering crops
• Open doors and vents whenever conditions allow
• Hand pollinate peach blossom
• Start sowing and planting
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