By our calculations, you should look at sowing Purple Vienna about 35 days before your last frost date.
For best taste, harvest when the bulb is 2.5 inches (6 cm) in diameter. Larger bulbs get woody.
As Purple Vienna is very hardy, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.The name comes from the German Kohl (which means “cabbage”) plus Rübe / Rabi (which means “turnip”)