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Common Milkweed (Asclepias Syriaca) Growing & Care Guide for Gardeners

Article by Dean Ravenscroft, Ph.D. - Updated 31st Jan 2024

At a Glance: Asclepias syriaca - (Common Milkweed)
  • Plant Characteristics: Features broad leaves and globular, fragrant pink to purple flower clusters. This plant is a crucial food source for Monarch butterfly caterpillars and attracts a variety of pollinators.
  • Growing & Care: Thrives in full sun and well-drained soil. It's drought-tolerant and adaptable to various conditions. Spreads through rhizomes and seeds, so it may require management in smaller gardens.
  • Tips for New Gardeners: A great plant for beginners, especially those interested in supporting butterfly populations. Be aware of its spreading nature and the potential for toxicity if ingested.

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, and are rated as UK hardiness H4 (hardy to -10°C (14°F)).

Common silkweed
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 and Monarch Butterfly
Silkweed flower with visiting Monarch Butterfly, photograph by Judy Gallagher; CC.

Gardener's HQ Guide to Growing Common Milkweed/ Silkweed

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
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.

Asclepias syriaca flowers
Cloese up of Asclepias syriaca flowers in bloom, photograph by Andreas Rockstein; CC.

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Asclepias syriaca Growing and Care Guide

  • Scientific Name: Asclepias syriaca.
  • Common Name: Common milkweed, Butterfly flower, Silkweed, Silky swallow-wort, Virginia silkweed, Common silkweed.
  • Growing Zone: USA: 3 to 8 / UK: H4.
  • Life Cycle / Plant Type: Perennial.

Plant Details

  • Plant Height (Inches): 36 to 60.
  • Plant Spread (Inches): 12 to 36.
  • Time of Bloom: Summer.
  • Flower Details: Pink.
  • Leaf Foliage: Green.
  • Growth Form: Upright / erect.

Ideal Growing Conditions

  • Best Light Conditions: Full sunlight.
  • Rate of Growth: Average pace.
  • Suitable Soil Types: Acidic, Clay, Loamy, Neutral, Sandy, Well drained.
  • Soil Moisture: Moist.

Caring Conditions

  • Level of Maintenance: Low.
  • Propagation: Seeds.
  • How to Prune: Not usually required.

Further Information

  • Can Attract: Butterflies.
  • Tolerant of: Deer, Drought, Erosion, Dry Soil, Shallow-Rocky Soil.
  • Family: Apocynaceae.
  • Closely Related Species: Adenium, Allamanda, Amsonia, Asclepias, Nerium, Pachypodium, Wrightia, Vinca.

I hope that you enjoyed this guide on how to grow Asclepias syriaca. You may also enjoy the following Gardener's HQ growing guides: How to grow Catharanthus and Oxypetalum plants.

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