When to Harvest Potatoes and How to Store Them: Clamps and Indoor Methods

Growing your own potatoes is one of the most rewarding parts of a vegetable garden, but knowing exactly when to lift them – and how best to store the crop – makes all the difference between firm, flavour‑packed spuds and a bag of wasted tubers.

Below you’ll find clear guidance on harvesting both early and maincrop potatoes, followed by practical tips for storing them either outdoors in a traditional clamp or indoors in crates and sacks.

Harvesting at the right moment ensures maximum flavour, prevents diseases such as late blight from spoiling tubers in the ground, and gives you potatoes that will store for months rather than weeks.

Why Timing Matters

Early Potatoes (First and Second Earlies)

First earlies are usually ready 10–12 weeks after planting (late June to early July in most of the UK), while second earlies follow about two weeks later. Dig up a test plant once the flowers open; tubers should be roughly the size of a hen’s egg. Because their skins are thin they don’t store for long, so lift what you need for the next fortnight and leave the rest in the ground for up to three weeks, protecting foliage from blight where possible.

Maincrop Potatoes

Maincrop varieties are ready 18–20 weeks after planting, usually from late August through September. Wait until the foliage has yellowed and died back, then cut the tops off and leave the tubers in the soil for 10–14 days to allow skins to harden. This ‘curing’ period improves their keeping quality.

General Signs of Readiness

Regardless of variety, potatoes are ready when: leaves have yellowed and are starting to collapse; the skins of a test tuber do not rub off easily with your thumb; and the weather is dry enough to lift without compacting the soil.

Lifting and Curing the Crop

Choose a dry day and use a fork, starting well outside the row to avoid spearing tubers. Lift the whole root, shake off loose soil and allow the potatoes to dry on the surface for a couple of hours. Brush off any remaining soil but do not wash.

Storing Potatoes Outdoors in a Clamp

A clamp is a simple, earth‑covered mound that keeps potatoes cool, dark and frost‑free without using electricity. Choose a well‑drained spot and lay a 15 cm (6 in) bed of straw or bracken on the ground. Pile the cured tubers into a pyramid no more than 1 m high, packing straw between layers to improve ventilation.

How to Build a Clamp – Step by Step

• Dig a shallow trench 30 cm (12 in) wider than the pile and line it with straw.
• Heap the potatoes, adding straw between each 30 cm (12 in) layer.
• Cover the pyramid with 15 cm (6 in) of straw followed by 15 cm of loose soil, shaping it into a smooth mound.
• Insert a small bundle of straw as a ventilation chimney at the apex and cap it with a tile or slate to shed rain.
• Mark the south‑facing side and always open the clamp here when removing tubers, resealing it firmly afterwards.

Storing Potatoes Indoors

For long‑term indoor storage choose only sound, blemish‑free tubers. Place them in breathable hessian or paper sacks, or stack them in shallow wooden crates, and keep them in a dark, frost‑free room at 4–8 °C with good air circulation. A garage, cellar or unheated spare room often works well.

Routine Checks

• Check sacks every fortnight and remove any tubers that show soft spots or sprouting.
• Keep the storage area dark; exposure to light turns potatoes green and bitter.
• Maintain airflow by leaving a small gap beneath crates and between sacks.

Key Takeaways

Harvest earlies as soon as the plants flower; lift maincrops after foliage dies back and cure them before storage. Use earth clamps for large outdoor crops or breathable sacks indoors at 4–8 °C. Check stored potatoes regularly and keep them dark, dry and well‑ventilated.