We love onions at GIY because they are one of those vegetables that it’s possible to become self-sufficient in, even if you don’t have a huge amount of space. A decent sized raised bed for example could produce a couple of hundred onions which would be enough for most families for up to a year. They are relatively low maintenance, easy to grow and store relatively well (but finding a suitably dry place to store them can be a challenge is wet Irish winters). Above all, there’s nothing better than having onions hanging in your shed and knowing you don’t have to buy those dry, tasteless, imported supermarket onions this year!
Generally most GIYers grow from “sets” (basically baby onions) but you can also grow from seed. Sets will mature quickly and are pretty much fool-proof - they are however more expensive than seed. Order sets early – the best varieties sell out quickly. Dig in some well rotted manure or compost the previous winter and apply an organic fertiliser (like chicken manure pellets) before sowing. Don’t plant onions in the same place year after year. Include in crop rotation.
Sets: sow 4 inches apart in rows 8 inches apart in March/April. Hold off if the weather is very cold – onion sets won’t do well in cold, damp soil. Push the set in to the soil so that the tip is just about visible above the surface. Firm in well. Frost can “heave” the sets from the soil at night – if this happens push them back in the next day. Seed: Sow in module trays from February and transplant when seedlings are well established.
Onions hate weed competition so keep your onion bed weed free. Hoe carefully around the bulbs every week or so and hand weed if necessary. Water if weather is dry or mulch (but remove mulch when bulbs start to form) – but never overwater. An occasional liquid feed will help.
Onions are ready to harvest when foliage turns yellow and topples over (approx 20 weeks after sowing). Gently loosen the soil around the onions at this point (or turn the onion very carefully and very slightly in the soil) and leave for another two weeks. Loosening the soil like this allows the onion to expand in the soil. Then lift carefully. Onions can be eaten fresh from soil. For storage, leave to dry on rack in sun (or indoors in greenhouse/polytunnel if weather is wet) for about 10 days. Then plait them in ropes or hang in nets. If there is a more impressive sight than an onion rope, we’ve yet to see it. Make sure to store them somewhere very dry - if there is any moisture at all in the air, the onions may rot. Check the rope frequently and use/remove any onions that are showing any signs of softening.
Most serious disease is onion white rot which causes leaves to yellow and wilt and bulb gets white mould. No remedy but to remove and burn. You can not grow onions in that spot for up to 7 years.