Asclepias syriaca. A once abundant native that has been pushed off of farms by more effective herbicides. Even small plantings of Asclepias can help the struggling Monarch butterflies. This genus is the only one that their larva feed upon. Best in its own area so it can spread by rhizomes. Grows 12-30" tall by 12-18" wide. Blooms all summer. Full sun. Plant in well-drained soil. Zones 3-9.