Washing and inspecting

Spread the lifted clump on newspaper or a tarpaulin. Use a hose or a bucket of water and a soft brush to wash off all the soil. This is not cosmetic — soil harbours slugs, disease spores and rot. You cannot inspect what you cannot see. Rinse until the tubers are clean enough that you could photograph them.

Now look closely. Healthy tubers are firm, plump, with taut skin and no soft spots. They feel like a raw potato, not a bruised peach. The neck where each tuber joins the central stem is the weak point. Inspect it carefully. A tuber with a rotten or shrivelled neck is worthless no matter how fat the tuber itself looks, because the neck is where new shoots emerge. Discard any tuber that feels spongy, smells sour, or has visible mould.

Check the crown — the woody hub where all the tubers radiate from. This is where the growth buds (eyes) sit, just above where each tuber neck joins the stem. You are looking for small raised bumps, sometimes pinkish, sometimes pale green. These are next year's shoots. A clump with a healthy crown and multiple visible eyes is ready to store or split.