Greetings crop pickers, here's the run down of the current top 12 polytunnel crops. Each of our 'Top of the Crops' have detailed growing guides, working with author and long-time polytunnel gardener, Andy McKee, we have produced a series of guides complete with all the do's and don'ts of growing the most popular crops. Whether you are looking to try growing something new, or just want to improve your existing crops these guides will make sure your polytunnel gardening is a big hit with all the family...
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Onions have been an important part of our diet since the Bronze Age, and after ripening (also known as 'curing') are hung for storage through the cold winter months. However, by the end of the spring, onions in store have usually started to sprout or rot, leaving a gap of several months before the first of the new harvest are ready.
Early overwintering onions (sometimes called 'Japanese onions') were developed to shrink this gap, but they still don't ripen until July and winter losses can be high. In the polytunnel, however, overwintering onions really come into their own, giving bigger and better bulbs.
Varieties: 'Senshyu Yellow’, ‘Electric’ (Red)
Sowing: For the most reliable results, buy onion sets rather than seed. Prepare the ground in May by gently forking plenty of compost or manure into the top layer of the soil: it should have settled nicely by the time you come to plant the sets, in July or August. Plant them with the tops just showing, in rows 10cm apart for easy weeding. If you're planning on eating the bulbs early to fill the 'onion gap' set them at spacings of 5cm within the row, but if you're going to leave them a bit longer and want bigger bulbs, then increase that to 10cm.
Just keep the onion bed free from weeds and well watered. On lighter soils, mulching round the bulbs with compost can help the bed stay moist during hot weather.
Diseases and pests: Newly planted sets sometimes succumb to moulds and mildew, so remove any that seem to be struggling. The emerging leaves are often attacked by slugs. Once the plants are growing strongly this won’t bother them, but for the first few weeks you will need to check the onion bed with a torch, about an hour after dark, on any humid evenings. If you can see slugs and snails about outside, you can guarantee that the ones in the tunnel will be munching on your onions!
Onions need to ripen before use, otherwise the flavour can be quite harsh. You can tell when the bulbs are ripening because the leaves turn yellow and fall over, but if you need to harvest them earlier than this, you can cheat; fold the leaves over firmly at the neck, partly lift the bulbs out of the ground with a fork, and reduce the amount of water that you give. After a week or two like this they're ready to cook with, but if you plan on storing them for a while then move them to a sunny spot with good air circulation (I use a suspended shelf in my polytunnel) and leave them for a further two or three weeks, until the necks have dried out completely. Then you can braid them for storage if you like, or pop them into net bags for hanging up somewhere cool and dry.
Recipe: Where to start? Onions are an extremely flexible ingredient that have masses of uses. You’ll always find a way to use your onions.