Late planting, not enough water, too much nitrogen, or planted too close together. Crowded radishes won't "bulb" properly and judging by the length of the stems and the skinny roots I'm 99.9% certain this was the cause.

From the soil mix I assume you are doing a square foot garden. How close did you plant them?

Rodney

Thanks!

You are probable right I tried square foot gardening, and used the "Zip-Zap" method to make 4 squares and planted 4 seeds per square. But I think a lot of room was wasted in between and they were indeed a little tight. I hope that is the problem.
Water should not have been a problem.

How much peat moss was in the mix relative to other components? One possibility is that the soil was too acidic. Radishes like a neutral soil.

it was about 1/4- 1/5 of the soil.

This post was edited by Kay17jan on Tue, Jun 24, 14 at 15:47