Culture
Easily grown in average, dry to moist, sandy or gravely, well-drained soils in full sun. Tolerates part shade. Best in sunny locations with sandy loams. Drought tolerant. Easily grown from seed, and will self-seed in the landscape if seed pods are not removed prior to splitting open. Likes hot dry soils, but tolerates moist garden soils. Plants will spread by rhizomes but are not considered invasive. Performs poorly in wet soils. Difficult to transplant because of deep roots.
Noteworthy Characteristics
Asclepias hirtella, commonly known as tall green milkweed or prairie milkweed, is an upright herbaceous perennial that typically grows to 3’ tall on one or more unbranched stems. This is an uncommon species that is native to upland prairies, rocky glades, sandy wetland margins, roadsides, pastures and abandoned fields from Ontario and Minnesota south to Kansas, Louisiana and Georgia.
Most milkweed plants (Asclepias genus) are noted for their unique and complicated flower structure, the thick milky juice which oozes from broken stems and leaves, their long pointed seedpods, and the almost magnetic attractiveness of their flowers to visiting butterflies and moths.
Alternate leaves (to 2-6” long) of tall green milkweed (most milkweed species have opposite leaves) have a very narrow-linear to linear-lanceolate shape.
Rounded, almost spherical, 2-inch diameter umbels, each containing 30-100 tiny, purple-tinged-greenish-white flowers (to 1/8” across), develop in the middle to upper leaf axils in late June-August. Each individual flower has 5 sepals (lobed calyx), 5 petals (lobed corolla), and 5 upright cup-like hoods (horns absent). The reflexed 5-lobed corolla curves backward and downward toward the center of the umbel, displaying the 5 hoods which are in general a key diagnostic feature of milkweed family plants. Flowers are followed by smooth narrow seedpods (4-5” long) which split open when ripe to release numerous silky-tailed seeds for dispersal by the wind.
Tall green milkweed is distinguished from many of the other species of milkweed by its narrow alternate leaves, greenish-white flower umbels, absence of horns in the flower hoods, and its very floriferous bloom.
Genus name honors the Greek god Asklepios the god of medicine.
Specific epithet means rather hairy.
Common names are in reference to plant size and typical habitat.
It should be noted that the monarch butterfly, possibly the best known butterfly in North America, needs milkweed plants in order to survive. Monarchs migrate into the U.S. from Mexico in spring to lay their eggs on milkweed species plants. Caterpillars hatch from the eggs and consume the milkweed plant foliage as food for growth and development. Mature caterpillars next spin a chrysalis which hangs on a milkweed stem until it later emerges, through the miracle of metamorphosis, as an adult butterfly. Flower nectar is consumed by adult butterflies as a valuable food source. The adult butterfly eventually migrates into Mexico for winter. Recent significant declines in monarch butterfly populations in North America are believed by many experts to be related to a corresponding significant decline in milkweed plants which in large part has been caused by an increased use of glyphosate herbicides around food crop areas where glyphosate-tolerant (Roundup Ready) crops are being grown.
Problems
No serious insect or disease problems. Watch for aphids.
Uses
Butterfly gardens, meadows, prairies, or naturalized/native plant areas. Borders. Cottage gardens. Rock gardens.
Seed pods are valued in dried flower arrangements.