They average 1 to 2 pounds in weight (450 to 900g), and 6 to 8 inches across (15 to 20 cm.) They can grow as big as 4 pounds (1.8 kg.)
They have a sweet, mild taste, and being large and quite round, are a great size and shape for hamburgers.
These onions tolerate cool weather while growing, and grow well in short growing seasons. They take just 95 days from seed (depending on where you are and how you start them.)
Have a better storage life than other Spanish onions.
Developed in 1887 by a gardener for the Marquis of Ailsa at Culzean Castle in Maybole, South Ayrshire, Scotland. From Culzean Castle, as indeed from the Ayrshire coast, you can see the island of Ailsa Craig (from the Gaelic “ailsse creag”, which means “fairy rock”). Either the Marquis or his gardener named the onion after this island. Some sources say the name was chosen because the island looks like an onion (more like the bottom of an onion actually), but this is just conjecture with no solid backing for it. Besides, some people think the island looks more like a crusty roll.