(USDA Organic) Onion ‘Walla Walla’ is a large, sweet Spanish onion with light-brown skin and mild white flesh. Famous for its sweet flavor in fresh eating, Walla Walla” is a medium to large mild onion with white flesh and light brown skin. Very cold hardy and can be directly sown in mid-spring. Spanish type (and American) onions require long days for bulb production.