Just to clarify, because several replies have mentioned the compost pile -- these weren't growing in my compost pile. Last winter, I buried my kitchen scraps in a newly created bed instead of composting them, anticipating they would feed the worms and other critters over the winter, and help the soil become better for when I planted shrubs in those new beds. I've actually never had anything grow in my compost pile.
That said, 12-18 months ago, I dumped out a bunch of old containers, so I could store the empty pots. This spring, I had a volunteer petunia, and a volunteer cherry tomato plant. It had been three years since I'd used that container for cherry tomatoes -- apparently the roots still had life in them even though the container itself looked totally empty other than dirt.
