I have three Giant Hardy Hibiscus. I kept them all together through the winter, they all went dormant. Only one broke dormancy and is now24" tall, one got some green buds and 1/2" of green stem, but I set it outside when the weather warmed up, but it never grew. The other one never got any green buds or green stem, but the roots are green. They sit on a patio table on the south side of the house, get a lot of sun. I watered them all the same. The two plants still haven't grown at all. Is there anything I can do to make them break dormancy?