Yes! I also fail at radishes. Mostly they don't bulb up, but I am also acquainted with the "very small bitter rocks with worm holes in them" you describe. I have no idea what I'm doing wrong. But I've given up and now grow salad turnips (Hakurei is the variety I like), which do work reliably and taste nicer too. They do take about a week or two longer than radishes, however. 35 days.