Asclepias incarnata

Swamp Milkweed

 Swamp Milkweed, Photo © by Earl J.S. Rook
Swamp Milkweed
Photo © by Earl J.S. Rook

Flora, fauna, earth, and sky...
The natural history of the northwoods

Name:
  • Asclepias, a Greek name in honor of the god of medicine, 'asklepios (Asklepios).
  • incarnata, from the Latin, in, "in"; carn, "flesh"; -atus, "like, resembling"; hence, "flesh colored", a reference to the dusty rose color of the flower.
  • Common name from its preference for a wetland habitat. Strickly speaking, a misnomer, as swamps are by definition wooded wetlands and this plant thrives in the sun.
  • Other common names include Red Milkweed, Silkweed

Taxonomy:
  • Kingdom Plantae, the Plants
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Magnoliopsida, the Dicotyledons
      • Subclass Asteridae
        • Order Gentianales, the Gentians
          • Family Asclepiadaceae, the Milkweeds
            • Genus Asclepias, the Milkweeds
  • Taxonomic Serial Number: 35710

Description:
  • A tall, moisture loving, herbaceous perennial of wet places.
  • Leaves usually opposite and occasionally whorled; long and pointed, oblong, lanceolate, with tiny hairs along smoothly wavy edges, veins beneath, and short petiole (leaf stalk); 4"-7" long, 1"-2" wide. Leaves bend upward on either side of the prominent midvein, like a boat keel.
  • Stem brown or purplish, single or clustered; sturdy, erect, smooth, branched above; 36"-48" tall, with a loose, pithy central canal and milky juice. A velvety band of hairs extends downward from the junction of leaves on each side of stem.
  • Root system shallow, fibrous; rhizome oblong, 1" in diameter, knotty, surrounded with rootlets, 4"-6" long, yellow-brown externally, white internally
  • Flowers bright pink, rose-purple, or, rarely, white, fragrant, in large dense umbels to 3"-4" across at stem tips. Bloom July - September
  • Fruit an erect pod about 3" long, on short stem; smooth or slightly hairy
  • Seed oval or pear-shaped, somewhat flat, about 3/8" long, with tufted silky hairs; spread by wind.
  • All parts poisonous

Identification:
  • A waterside plant of sedge meadows
  • Distinguished from the similar Joe Pye Weed (Eupatorium maculatum) by its somewhat brighter flowers, its somewhat lighter green leaves, and its distinctive milkweed seed pod.
  • Field Marks
    • Narrow, upright form with opposite leaves
    • Flat-top cluster of rose pink blossoms

Distribution:
  • Southern Canada and Maine, west to North Dakota and south to Forida and New Mexico.
  • Near the northern edge of its range in the BWCA.

Habitat:
  • Edges of ponds and moist soils, wet meadows, shallow waters. Banks and flood plains of lakes, ponds, and marshes. Ditch edges, dikes, swamps, wet prairies, and poorly drained spots.
  • Soil neutral to slightly acid; will tolerate heavy clay

Associates:

History:

Uses:
  • Pods dry beautifully and are often used in arrangements.
  • Flowers used fresh in arrangements, but ends must be seared to prevent wilting.

Reproduction:
  • Reproduces by seed and vegetatively by underground rootstalk
  • Flowers June to August

Propagation:
  • Propagate by division, or by seed sown outdoors in fall.
  • Sow at 68ºF, germinates slowly
  • Produces a heavy crop of "volunteer" seedlings in many gardens.

Cultivation:
  • Herbaceous perennial forming stately clump of upright stems with long narrow leaves and heads of fragrant soft mauve pink flowers, composed of many small intricate flowers.
  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Cultural requirements
    • Soil rich, wet, very muddy to average garden moisture
    • Full sun
    • Spacing 2½'-3' apart
  • One of the few ornamentals that thrives in mucky clay soils.
  • Will thrive in average garden soil, so long as it doesn't dry out completely, especially in spring. Actually quite drought tolerant despite penchant for water.
  • Attracts a profusion of butterflies; an excellent addition to the butterfly garden; both a nectar source and host plant for the Monarch Butterfly.
  • Often attacked by aphids, both in the wild and in the garden (typically on the stem); generally not harmful to the plant. May be removed with a hard stream of water or sprayed with insecticidal soap, or simply left alone. Plant toward rear of garden if you prefer to view the flowers without seeing the aphids.

Links:

Comments:
  • A favorite plant for the butterfly garden or wild border. Easy to grow, long flowering, attractive seedheads, and a Monarch magnet.

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Last updated on 4 March, 2006