OSC Walla Walla Onion Seeds (Super Sweet Type). Start seed indoors as early as you can as the bigger the transplant, the better the mature onion will  be. Walla Walla withstands considerable cold, so if possible, you can start seed in a cold-frame to get a jump on the season. Yellow fleshed super sweet onion. Size of harvested bulb is variable from 5-15 cm. This is not a long-term storage onion so enjoy them fresh. Long Day variety. Approximately 140 days to harvest.