When to harvest 'walla walla' onion

Lift a test plant once it looks close to size — appearance above ground tells you little. 'Walla Walla' Onion is harvested from below ground, so the timing cue is size rather than colour — and the only reliable way to check is to lift one. Ease a single plant up when you think it is close: if it is the size you want, harvest the rest over the following weeks. Roots left too long in the ground turn woody, split, or bolt, and the flavour coarsens.

Loosen the soil alongside the row with a fork before pulling, rather than yanking by the leaves. Pulling on the tops snaps them off and leaves the root behind, and bruised roots store badly.

Brush soil off rather than washing if you plan to store — a wet skin rots. Keep somewhere cool, dark and slightly humid; a box of barely-damp sand in a shed or garage is ideal.

Leaving 'walla walla' onion in the ground "to get bigger". Past its window it goes woody and splits — size is not the same as quality.