I just made a post this morning about growing radishes in pots.
https://steemit.com/garden/@jordanmccraw/planting-radishes-in-containers

I think that the fertilizer pellets on the surface might be too much for them. Try putting rich compost into the dirt and mixing it around. The compost acts like a slow release fertilizer. Every 4 weeks water with a solution of 20-20-20 or 10-10-10 fertilizer to keep replenishing the nutrients.

Upvoting and following.