Starter plant in a 2.5 inch pot. Apclepias verticillata or Whorled Milkweed is another real butterfly magnet. Perennial 1-3 feet tall hardy in zones 4-11. Flowers: June – September. Found on dry, heavy soils of prairies, rocky hillsides, and sandy open woods. A delicate white clusters of blossoms and graceful plant that often forms colonies.