Timing Your Maincrop Harvest

Maincrop potatoes are the backbone of the winter store. Unlike earlies, which are lifted and eaten fresh in summer, maincrops are left in the ground to bulk up and set their skins. In most UK gardens and smallholdings, that means lifting from late August through September, though it varies with variety and weather. The signal to start is when the foliage—the haulm—turns yellow and dies back. Once that happens, stop watering and wait a fortnight if you can. This lets the skins toughen, which is your first defence against storage rots.

If blight has been a problem, cut the haulm to ground level two to three weeks before you plan to lift. This prevents spores washing down to the tubers and gives the skins time to set. Choose a dry day with a light breeze. Wet soil clings to potatoes and encourages disease, so if the forecast is unsettled, wait. You want to lift before the first hard frost, as frozen tubers turn to mush.

Lifting Without Damage

There is a knack to lifting potatoes without spearing them. Use a garden fork rather than a spade, and push it into the soil a good 30 centimetres away from the stems. Lever gently upwards and back. You will feel the fork meet the nest of tubers. Lift the whole plant and shake off the worst of the soil. Leave the potatoes on the surface for a couple of hours to dry, but do not leave them in bright sunshine for long—light turns them green and makes them bitter.

As you gather them, sort into two piles. The first is for immediate use: any with cuts, bruises, slug holes, or patches of blight. The second is for storage: only firm, clean, undamaged tubers. Be ruthless. One rotten potato can spoil a whole sack. Handle them like eggs; every knock is a potential entry point for mould.

Curing for Longevity

Curing is the step most beginners skip, and it makes all the difference. It heals small grazes and thickens the skin, turning a fresh tuber into a keeping potato. After lifting, move your keepers to a dark, airy, cool but frost-free place. An ideal temperature is 10–15°C. Spread them in a single layer in trays or wooden boxes, or leave them loose in paper sacks with the tops folded open. Leave them for ten to fourteen days.

Once cured, brush off any remaining dry soil. Never wash potatoes before storage—moisture invites rot. A soft brush or your hands is all you need. The skins will feel dry and papery, and any small wounds will have healed over. Now they are ready for the long haul.

Choosing and Preparing Storage Containers

Paper sacks are the smallholder’s friend. They breathe, they block light, and they stack neatly. Plastic bags or sealed bins are a poor choice because they trap moisture and create the perfect conditions for rot. Fill paper sacks loosely—no more than two-thirds full—and fold the top over rather than sealing it. This allows air to circulate while keeping the darkness in.

• Use clean, dry paper sacks. Old paper feed sacks work well if they are free of holes and chemical residues.
• Label each sack with the variety and the date you stored them. You will thank yourself in February.
• If you prefer crates or boxes, line them with newspaper and leave gaps between them for airflow.
• Never store potatoes in the same sack as onions or apples. Those produce ethylene gas, which makes potatoes sprout.

The Ideal Storage Environment

Your potato store should be dark, cool, frost-free, and well ventilated. Aim for a steady 4–7°C. Warmer than that and they will sprout; colder and the starch turns to sugar, giving you sweet, discoloured tubers that blacken when fried. Light is the enemy of flavour—it triggers greening and the production of solanine, which is mildly toxic. A garage, an unheated shed, or a spare stable that stays frost-free can all work well.

Stack your sacks no more than three high, and keep them off cold concrete floors if you can. A wooden pallet or shelf provides a useful barrier against damp and frost. Check the space regularly for signs of damp or mice. Good air movement around the sacks is essential, so do not cram them into a corner.

Using and Monitoring Your Store

Once stored, check your potatoes every two to four weeks. Remove any that are rotting, sprouting, or shrivelling. One bad tuber can taint its neighbours, so act quickly. Use the damaged ones first—they will not keep as long. Smaller potatoes also tend to dry out faster, so enjoy those before they go wrinkly.

If sprouts appear, rub them off and use those potatoes soon. A little sprouting is not a disaster, but it signals that the store is too warm. With luck and a cool corner, your maincrop harvest will last until April or May. There is nothing quite like digging into your own store for a Sunday roast when the ground outside is frozen. Enjoy the fruits of your labour—mashed, roasted, or chipped—right through the winter.