My radishes did the oddest thing this year. I planted them April 26, and by May 10, they still hadn't come up. I'm 99.99% certain they were well watered; the soil felt good and moist.
I was just thinking about what I might put in there instead, and we got 6" of wet, heavy snow, probably on May 13. It melted in a couple of days, and within 48 hours, most of the radishes were up. They're all up now, but I still think that's about as weird as it gets. Were it not for the seeds' stubborn refusal to germinate, I'd have radishes right about now, too