Why Are My Stored Potatoes Going Soft and Sprouting?

A well-grown potato crop deserves to last through winter, but too often the store that looked fine in October is a mess of sprouting, rotting, or shrivelled tubers by December. The causes are almost always environmental — wrong temperature, wrong light, wrong humidity, or storing diseased tubers that then infect their neighbours. Getting storage right is straightforward once you understand what potatoes actually need, and the difference between a well-managed and a poorly managed store can be six months of eating versus six weeks.

Too warm — sprouting and shrivelling

Potatoes stored above 10°C will begin sprouting relatively quickly as the tuber's dormancy breaks. Above 15°C, sprouting is rapid and the flesh shrivels as moisture is directed into the growing sprouts. Kitchen potato racks, warm cupboards, or a shed that warms up significantly in autumn sunshine are all too warm for long-term storage. The ideal temperature range for maincrop storage is 4–7°C — cold enough to maintain dormancy but not so cold that starches convert to sugars. A cool cellar, an insulated garage that stays frost-free, or a dedicated cool shed achieves this reliably.

Any light causes greening

Even dim light reaching stored potatoes will cause greening — the production of solanine — over time. Storage must be in complete darkness. Paper sacks, hessian bags, or wooden crates lined with newspaper all work well. Never store in clear plastic bags or on open shelves with any ambient light. Check your store periodically with a torch rather than turning on the main light — it makes little practical difference in a quick check but habit matters over many months.

Too humid or poorly ventilated

High humidity without airflow encourages condensation and mould growth on the potato skin, leading to soft patches and rot. Store potatoes in containers that allow airflow — wooden slatted crates, paper or hessian sacks with the tops folded over loosely, or open-topped boxes in a cool space. Never seal potatoes in airtight plastic containers. Conversely, very dry conditions cause shrivelling. Moderate humidity with good airflow is the target — a traditional cool potato store achieves this naturally.

Diseased tubers rotting the whole store

A single tuber with soft rot, neck rot, or blight infection can spread to every potato around it within two to three weeks. Sort ruthlessly at harvest: feel every potato and discard any with soft spots, wounds, or off-smells. Re-sort the store every three to four weeks through winter, removing any that are beginning to soften before they infect neighbours. This regular sorting is the single most important ongoing maintenance task for a potato store.