Onion Ailsa Craig

The Scottish exhibition onion, bred by David Murray at Culzean Castle in the 1880s and named for the granite island off the Ayrshire coast. Nearly 140 years on it is still the standard for large culinary onions — straw-yellow globes of 500 grams as a matter of course, and over a kilogram in expert hands.

For so large an onion the flavour is remarkably fine. Sweet, mild, never harsh, which makes it one of the few big onions genuinely worth eating raw — sliced onto a sandwich or over cheese rather than simply cooked down as a background note.

Size depends almost entirely on how early you start. A January sowing under cover gives the long season the big bulbs need; sow in March and you will still get excellent onions, just smaller ones. Give them room, since crowding costs you more size than anything else.