Asclepias verticillata - Horsetail Milkweed
This frosty green milkweed is native to the prairies of the eastern U. S. It grows 2' to 3' tall and blooms fragrant clusters of white flowers that open midsummer. Side branches continue blooming for weeks. A larval food for Monarch butterflies, this Asclepias blooms later than its cousins, giving butterflies one more food source in mid-summer.
In the wild, Whorled Milkweed is found in dry locations with sandy soil, but it will tolerate moist garden soil. It spreads gradually, forming a lovely sweep - enchanting when the drifts are in full bloom.
Asclepias verticillata is deer and rabbit-resistant, but is toxic to livestock and should not be allowed to spread to hayfields. It's perennial in all zones from 3-11. Sow seeds in fall or cold stratify at 40F for 2 to 3 months.