There is a moment in late summer that every onion grower learns to watch for. One morning the fat, green tops that have been standing proud all season suddenly flop over at the neck, as if the whole row has had a long lunch. That collapse is your signal. The bulb has finished swelling and is beginning to ripen, drawing its last reserves down from the leaves into the base.
For maincrop onions sown or set in spring, this usually happens between late July and early September, depending on variety and where you garden. Japanese or overwintering types such as Senshyu Yellow and Radar tend to be ready a few weeks earlier, often from late June. Shallots and garlic follow a similar rhythm.
Resist the temptation to lift the moment the first top bends. Give the row another week or ten days, but only if the weather is dry. If heavy rain is forecast, get them up sooner rather than later, because ripe bulbs sitting in wet soil are an open invitation to neck rot.
You can tell a bulb is ripe by feel. Ease one from the ground and look at the neck, where the leaves meet the shoulder. On a ready onion it will feel soft and papery, almost hollow. If it is still thick, firm and juicy, the bulb is not finished and will not store well.
Never pull onions straight up by the stems. The neck is the weakest point on the whole plant, and a sharp tug can crush the tissue that keeps rot out of the bulb all winter.
Handle them as though they were eggs. Every bruise, every nick from a fork tine, is a small doorway for mould. Onions that are accidentally speared should be set aside and eaten within a week or two rather than stored.
If the weather turns wet just as you are lifting, spread the bulbs in a single layer somewhere under cover, such as a greenhouse bench or a shed floor, rather than leaving them in the mud.
Drying, or curing, is what turns a fresh onion into a keeper. The aim is to drive moisture out of the neck and the outer skins until they rustle. Skip this and even perfect bulbs will rot in the net.
In a decent summer, the traditional method works beautifully. Lay the onions in a single layer on a warm, sunny, well-ventilated surface, out of reach of pets and footballs. A patio, a gravel path or a rack of old pallets is ideal. Turn them every couple of days so both sides dry. Two to three weeks is usually enough, though a damp August can stretch it to four.
If rain is a regular visitor, dry them indoors instead: a greenhouse, polytunnel, garage or airy porch will do. Good airflow matters far more than heat. A gentle breeze through an open door beats a stuffy, warm room every time.
You will know they are ready when:
At this point, rub off the loose outer skin and trim the roots back to about 1cm. Some growers leave the tops on for tying or plaiting; others cut them to 5cm. Either works, provided the neck is properly dry.
Onions want three things from a store: cool, dark and dry, with air moving around them. A frost-free shed, garage, unheated spare room or brick outhouse is perfect. Aim for somewhere between 3°C and 10°C, though they will tolerate warmer conditions if the air is dry.
Net bags, old tights, string bags or slatted crates all work well. The important thing is ventilation, so never tip them into a sealed plastic box or a closed bucket. Hanging nets from a beam keeps them off cold floors and away from mice.
If you fancy the traditional look, plaiting is satisfying and practical. Leave the tops on after curing, then weave the dry leaves into a rope, adding bulbs as you go. Hang it in the shed and pull onions off as needed.
Check the store every few weeks. Remove any bulb that feels soft, shows grey fuzz or has a dark, sunken patch. One rotten onion can spread trouble to its neighbours surprisingly quickly.
Thick necks are the most common reason onions fail in store. They usually mean too much nitrogen during the growing season or lifting before the tops had properly collapsed. Eat these first.
Bolted bulbs, the ones that ran to flower in June, have a hard core and will not keep. Use them in the kitchen straight away.
White rot shows as a fluffy white fungal growth at the base with tiny black specks. Bin those bulbs, do not compost them, and avoid growing onions or leeks in that spot for several years.
Stored well, a decent crop of Sturon, Red Baron or Ailsa Craig will keep you in onions from September right through to March — a quietly satisfying thing to have hanging in the shed when the frost is on the ground.
Gate & Furrow shares practical, down-to-earth guidance on british kitchen gardening and allotment growing for readers across the UK.
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