radish problem

Afternoon all,
Having problems with radish's, I'd sown some cherrybelle seed probably about end of march in an approx 10-12inch pot, the seeds germinated with no problems and seem to be developing very well. once the greenery had got to 6-7inch (last week) I thought I'd try and pull a few as most of the books said they should have been ready by now.
I pulled the first one up and there was nothing on the end! So I carried on pulling the rest of the plants and it was the same situation! All I got was a thin red stem about 1.5 inch and then very very small white roots underneath!
What have I done wrong? Have I not left them long enough or is it maybe dud seeds?Too many seeds in the pot (prob had about 10 plants in the pot).
Considering radish is supposed to be one of the easiest produce to grow I'm really at a loss on this one!

Any ideas or help would be very much appreciated.
Thanks

Probably lack of water, or lack of nutrients, or both.

May I ask where you grew them?

Radish don't like it too warm and if they were in a greenhouse or indoors, that may explain it.

Thanks for the replies everyone,
They were grown in multi purpose compost, sown straight into the pot which was placed just outside the backdoor and is in a fairly shaded/sheltered spot. I watered them once a day until the weather started to warm up and then watered twice a day.
I have another variety in another pot so I think I'll see how they get on but will probably try the ones you suggested Jay.
Thanks again everyone.