I have always started my caladiums in the house and they move along fast. They are ready to plant out in late May or early June. See my photo top row, second from the left. Since my bathroom is the warmest room in the house they do well on the sill there. It is just too cold for too long here to plant them out directly. By cold, I mean less than 50 deg.
Caladiums (Caladium)
