Rover
Radish in the US

Radishes are cool-season crops, so you'll want to get them in the ground when it's not too hot. For folks in warmer spots, like zone 10, you can be sowing from January right through to May, then again from September to December. In cooler zones, say zone 3, April to August is your window. Sow the seeds directly into prepared soil, about half an inch deep and an inch apart. I like to do a small batch every couple of weeks, that way you get a steady supply rather than a big glut all at once. They don't really do well from plug plants, so direct sowing is the way to go.

Once your radish seedlings are up and growing, you'll need to thin them out. Give each plant about 2 to 3 inches of space, that'll let the roots swell up properly. If they're too close, you'll just end up with a lot of leafy tops and no radish. You can grow radishes in pots or containers too, as long as they're at least 6 inches deep and have good drainage. They're not fussy, but they do need that bit of room.