In "normal" conditions, you
In "normal" conditions, you need to check roots often for usable size (when roots are less than 1 inch in diameter) and young. Pick quickly as radishes will not remain edible for long and get spongy. If you have all tops and no bulb, the usual reasons are: 1. seeds are too crowded/lack of thinning, 2. weather too hot for spring-variety radishes.