How do I store a potato crop over winter?

The difference between potatoes that last until April and potatoes that go soft by Christmas is decided in the fortnight either side of lifting. Curing, sorting and darkness do almost all the work; the storage container is the easy part.

Step by step

1. Wait for the skins to set before lifting.Once the haulm has died back or been cut, leave the tubers in the ground for about two weeks. Rub a thumb across a skin — if it scuffs off, it is not ready. A set skin is what keeps rot out.
2. Lift on a dry day and handle them gently.Bruises and fork wounds are entry points for rot. Lift with a fork well away from the plant, work outwards, and drop tubers into a container rather than throwing them.
3. Dry them on the surface for a few hours.Spread them out somewhere airy and out of direct sun for two or three hours until the soil on them is dry and brushes off. Do not wash them — water on a stored potato is the beginning of rot.
4. Sort ruthlessly.Anything cut, speared, slug-holed, greened, scabbed through into the flesh or showing brown staining goes into an 'eat now' box or the bin. Only clean, whole, firm tubers go into store.
5. Choose a breathable container.Paper potato sacks, hessian sacks or a wooden crate lined with newspaper. The requirement is darkness plus air movement. Never a plastic bag or a sealed box — condensation forms and the crop rots.
6. Find a dark, cool, frost-free place.Around 4–8°C is the target. A garage, an unheated utility room, a cool cupboard or an insulated shed all work. Below freezing ruins them; above about 10°C they sprout early.
7. Exclude light completely.Any light greens the tubers, and green means bitter and unsafe to eat. A double-thickness paper sack, a covered crate or a dark corner does the job.
8. Check the store every two or three weeks.Feel for softness and smell for sourness. One rotting tuber turns liquid and spoils everything touching it. Remove any that are going and rub off sprouts as they appear.
9. Keep them away from onions and from fruit.Onions and potatoes stored together shorten each other's life, and ripening fruit gives off ethylene which encourages sprouting.

Tips

• Only maincrop varieties store well. Earlies have unset skins and are meant to be eaten within days — do not try to keep them.
• Set aside the damaged and scabbed tubers as an 'eat first' box and work through them before touching the store.
• Storing in the dark also matters for taste: potatoes exposed to light develop bitterness long before they look green.
• A cardboard box inside a hessian sack inside a cold garage gives useful insulation against a hard frost.
• If a store starts sprouting in February despite being cool, it usually means the temperature is creeping up rather than that the potatoes have failed.

Common mistakes

• Washing the crop before storing — Water and damaged skin together are exactly what soft rot needs. Store them dirty and wash them as you use them.
• Storing in the fridge — Cold below about 4°C converts starch to sugar, which makes them sweet and causes them to darken badly when fried or roasted.
• Using plastic sacks or sealed tubs — Potatoes respire. Trapped moisture condenses inside plastic and the crop sweats and rots within weeks.
• Storing the damaged ones with the good ones — A single rotting tuber can spoil an entire sack, and the damaged ones are the ones that go first.

Keeping on top of it

• Check sacks for soft or smelly tubers (every 2–3 weeks)
• Rub off any sprouts that appear (monthly from midwinter)
• Check the store has not dropped near freezing in a cold snap (during any hard frost)

Questions people ask