Obedient Flowers (Physostegia virginiana) The lavender flower spikes accent the water garden nicely. It is a very vigorous grower and gets 2' to 3' high. Grows in sun to part shade and tolerates deep shade. Plant in moist soil or water to 1 inch ceep. Overwinters well in water below freeze line. Blooms May thru frost. Hardy Zones 5-11.