Asclepias syriaca, better known as common milkweed or Silkweed, is a native North American wildflower found everywhere from the eastern United States through the eastern Prairie states to southern Canada.
These perennial beauties are often found growing in clumps along roadsides, fences, and in open meadows.
Plants perform well in USDA Zones 3 to 9; UK hardiness H4 (hardy to -10°C (14°F)).
Asclepias syriaca photograph by peganum.
Asclepias syriaca grows two to four feet (60 to 120 cm) tall with a straight stem topped by balls of fragrant purple ball-shaped blossoms.
The plant’s name comes from the milky sap that oozes when the stems and leaves are crushed or cut.
It’s a nutritional powerhouse for many insects, especially the monarch butterfly.
Silkweed flower with visiting Monarch Butterfly, photograph by Judy Gallagher; CC.
The common milkweed plant is easy to sow and quick to establish making it a popular addition to gardens.
This hardy plant blooms during the summer months and can handle a variety of humidity and temperatures.
It spreads both by tufted seeds and rhizomatous roots. The creeping subterranean roots take hold and spread quickly.
To propagate, cut root sections from already established plants and place them approximately 18 inches apart (45 cm), at a depth just deep enough to cover the roots.
Common milkweed plant, photograph by Nacho 13; CC.
If starting from seeds, place about 1 inch (2.5 cm) deep in the soil.
Stems will surface either alone or as part of a clump. Seedlings will flower by the second year.
Asclepias syriaca prefers full sunlight and well-drained soil, typically only needing watering in extremely dry conditions.
The small bit of maintenance required for Asclepias syriaca involves keeping it from spreading beyond the desired growing area.
The seeds will catch the wind and spread much like dandelions. Therefore, deadhead the flowers before seed set.
Ideally, establish a minimum of six plants if you wish to attract butterflies to your garden.
Cloese up of Asclepias syriaca flowers in bloom, photograph by Andreas Rockstein; CC.