Brought to the U.S. from the British Isles in 1887 by David Murray, gardener for the Marquis of Ailsa, Ailsa Craig heirloom onions are by far the largest onion you can grow in a short growing season. The key is to plant Ailsa Craig onion plants early and never let them slow down. If you are looking for show-size variety with which to win the county fair for largest onion, Ailsa Craig is it. Pump these onion plants up with lots of nitrogen to get them as big as basketballs. Ailsa Craig onions do not store well, so enjoy them soon after harvesting. Also known as the Kelsae Sweet Giant onions.