Early White Vienna
Kohlrabi in the US

Being a cool season crop, you'll want to get your kohlrabi seeds started in spring or fall, not when it's really hot. You can direct sow them or start them indoors for transplanting later. For spring, sow about 4-6 weeks before your last frost, and for fall, sow about 8-10 weeks before your first frost. Check your USDA zone for the best months – it's usually April to May and then July to August for zones 3 and 4, or March to April and August to September for zone 6. Sow seeds a half-inch deep, about 4 inches apart, then thin them to 6-8 inches if you're direct sowing. Keep the soil damp, and you can sow a small batch every couple of weeks for a continuous harvest.

If you started your seeds indoors, get them pricked out into individual pots once they have their first true leaves, like I do in my little greenhouse. Then, before planting them out, make sure you harden them off for a week or so, just to get them used to the outdoors. Plant them out in the garden about 6-8 inches apart in rows, giving each plant enough room for that bulb to swell. They don't need any special support, and you can even grow a few in decent-sized containers if your space is a bit tight.