How to store onions

Storage starts in the row

How well an onion keeps is partly settled months before you lift it. The RHS guides name four things in the growing season that matter.

Feeding. The RHS guide to onion neck rot, a disease that develops in store, says to avoid excess nitrogen and not to apply fertiliser late, which it defines as after July. The aim is hard, well-ripened bulbs.

Watering. Water in dry spells while the bulbs are growing, but stop once they have swollen in midsummer. The RHS says watering spring-planted crops after midsummer can mean they store less successfully.

Flower stems. Remove them as soon as they form. Bulbs that flower will not store well, the RHS says. Garden Organic breaks the stems off too.

Planting time. This decides how long the crop can last at all. The RHS says autumn-planted onions keep until early winter, while spring-planted or seed-raised onions keep well into the following spring. If you want onions for the whole winter, they need to be the spring-planted ones. See when to plant onions.

When to lift onions for storing

The months. The RHS says autumn-planted sets are ready in June and July, and spring-planted sets and seed-raised onions from July to October. Garden Organic gives mid-July to September, and an average time to harvest of 20 weeks.

The sign. Yellowing and toppling of the foliage shows that the crop is reaching maturity, the RHS says. Garden Organic describes the same thing: the leaves turn yellow and fall over.

Do not bend the tops over. It used to be common advice. The RHS now says it is no longer recommended.

How long to wait after the tops fall. The sources put it differently.

- The RHS says to harvest before the foliage dies down completely. - Garden Organic says to dig the bulbs up about two weeks after the leaves fall over. - Gardeners' World waits until the leaves have yellowed and stopped growing, and also lifts before the foliage has browned and died down completely.

These fit together well enough. Let the tops fall, give the bulbs a couple of weeks, and lift while there is still some life in the leaves.

Lifting without bruising

Choose a dry day. Garden Organic says so directly, and the RHS neck rot guide explains why: the bulbs should be kept dry at harvest, and the foliage and necks should dry quickly.

Loosen first. Garden Organic uses a hand fork to loosen the bulbs, which makes lifting easier. The RHS lifts carefully with a fork. Gardeners' World loosens the soil gently, then lifts the onions out.

Handle them gently. The RHS and Gardeners' World both warn about bruising. The RHS says bruised bulbs may rot in storage, and that any damaged onions should be used straight away. Gardeners' World says damaged onions do not store well, so use them first.

Sort as you go. The RHS neck rot guide adds a second group to keep out of the store: thick-necked bulbs. Use them immediately.

Drying: two weeks that decide the winter

How long. About two weeks, the RHS says.

Where. In full sun outdoors, on wire racks or something similar, so that air can move underneath the bulbs. The RHS neck rot guide lays ripe bulbs on their sides with the roots exposed to the sun. Gardeners' World spreads them on racks or on newspaper. Garden Organic simply says to leave the bulbs in the sun to dry before storing.

If it rains. A British August does not always oblige. The RHS says that in damp weather you should dry onions in a greenhouse or a well-ventilated shed. The neck rot guide says to cover the bulbs if rain threatens, or to dry them under cover.

When they are done. Store onions only once all the foliage is papery and dry, the RHS says. Gardeners' World listens for the skins to rustle.

Nets, trays and plaits

The RHS gives three ways to store dried onions.

1. Net bags. 2. Trays, in a single layer. 3. Plaits, tied and hung up.

The RHS neck rot guide lists the same kind of thing: wire netting, slatted shelves, or strings hung from the rafters. What they share is air on every side of the bulb. Garden Organic recommends plaiting as a way to save space.

Tops on or off? The RHS neck rot guide says to twist off the tops before storing. A plait needs the dry tops left on. Both appear in RHS advice, so choose by method: tops off for nets and trays, tops on for plaits.

Where to keep onions: light or dark?

On most points the sources agree. Onions want a place that is cool, dry and well ventilated. The RHS neck rot guide says warm, damp storage conditions favour the disease.

On light, they disagree.

- The RHS says to keep onions in a light place, and is explicit: do not store them in the dark, as this encourages sprouting. - Gardeners' World says to hang or string them in nets in a cool, dark, dry place.

We have not found a source that explains the difference. The RHS gives a reason for its advice and Gardeners' World does not, so we lean towards the RHS. What neither source disputes is that the store must be cool, dry and airy. A shed or garage with a window meets both the RHS conditions.

How long they last. Gardeners' World says they should last for months. The RHS is more exact: autumn-planted onions until early winter, spring-planted and seed-raised onions well into the following spring.

Neck rot, the disease of the onion store

The RHS describes onion neck rot as a fungal disease of onions and shallots, and occasionally garlic, caused by *Botrytis allii*. It can cause severe losses in store.

Why it catches people out. The plants usually look healthy while they are growing. Infection happens during growth and at harvest, but the symptoms usually do not show until the bulbs have been in store for several weeks.

What it looks like. The decay usually starts at the neck and can spread down the whole bulb. The scales turn soft and brown, as if cooked. A dense grey mould follows, and often hard, black, crust-like bodies. In the end the bulb dries out, sinks and mummifies. Gardeners' World describes brown marks and fluffy grey mould.

Where it comes from. The fungus can arrive on seed and sets, the RHS says, and it persists in the soil.

What you can do. There are no fungicides available to gardeners for it. The RHS list of defences is the method on this page:

- Buy seed or sets from a reputable company. - Do not grow onions for three years in soil where the disease has occurred. - No excess nitrogen, and no fertiliser after July. - Keep the bulbs dry at harvest and dry the necks quickly. - Use damaged or thick-necked bulbs straight away. - Store cool, dry and airy.

The RHS adds that white-bulbed cultivars are more likely to be attacked than red or yellow ones.

Checking through winter

Check stored onions regularly, the RHS says. Remove any that are decaying, and any that are sprouting early.

Rotting in store has more than one cause. The RHS growing guide says onions are prone to several fungal diseases, especially in damp conditions or if poorly stored. One soft bulb in a net is a reason to look at all of them.

Sprouting is the other way a store ends. The RHS links it to darkness.

Varieties that store well

If you are choosing sets for next year with the winter in mind, the RHS growing guide marks these as storing well.

- 'Sturon' - 'Centurion', which crops early - 'Red Baron', a red onion that crops in mid- to late summer - 'Marshalls Red Fen', also red - 'Rumba'

Remember the planting time as well. However good the variety, the RHS says autumn-planted onions keep only until early winter.

How much to expect. Gardeners' World gives an average yield of 30 large onions from a 3 m row. That is a useful figure when you plan how many nets or trays you will need.