HCMGAHenderson County Master Gardener Association

Swamp Milkweed

Asclepias incarnata

Swamp Milkweed
Swamp Milkweed with monarch butterfly
Swamp Milkweed flowers

Characteristics

  • Type: Perennial
  • Zone: 3 – 6
  • Height: 4 – 5 Feet
  • Spread: 2 to 3 Feet
  • Bloom Time: July – August
  • Bloom Description: White, Pink, Mauve
  • Sun: Full Sun
  • Water: Medium – Wet
  • Maintenance: Low
  • Suggested Use: Naturalize, Rain Garden
  • Flower: Showy, Fragrant
  • Attracts: Butterflies, Hummingbirds
  • Tolerates: Deer, Clay Soil, Wet Soil

Culture

With its showy flower clusters that attract butterflies and hummingbirds, Swamp Milkweed is underutilized in gardens. In moist soils or in a pond, it will thrive. The large, bright, terminal blossoms are made up of small, rose-purple flowers. Deep pink flowers are clustered at the top of a tall, branching stem, bearing numerous narrow, lanceolate leaves. Opposite, narrow, lance-shaped leaves line the erect, open-branched stem. Elongated, tan-brown seed pods persist into winter. Rich, wet, very muddy to average garden moisture. One of the few ornamentals that thrives in mucky clay soils. Swamp Milkweed prefers neutral to slightly acidic soil but will tolerate heavy clay. Easily grown in medium to wet soils in full sun. Surprisingly tolerant of average well-drained soils in cultivation even though the species is native to swamps and wet meadows. Plants have deep taproots and are best left undisturbed once established. Foliage is slow to emerge in spring.

Noteworthy Characteristics

Asclepias incarnata, commonly called swamp milkweed, is an erect, clump-forming, plant which is commonly found in swamps, river bottomlands and wet meadows throughout the State. It typically grows 3-4′ tall (less frequently to 5′) on branching stems. Small, fragrant, pink to mauve flowers (1/4″ wide), each with five reflexed petals and an elevated central crown, appear in tight clusters (umbels) at the stem ends in summer. Flowers are uncommonly white. Narrow, lance-shaped, taper-pointed leaves are 3-6″ long. Stems exude a toxic milky sap when cut. Flowers are followed by attractive seed pods (to 4″ long) which split open when ripe releasing silky-haired seeds easily carried by the wind. Flowers are very attractive to butterflies as a nectar source. In addition, swamp milkweed is an important food source (albeit somewhat less important than upland species of Asclepias) for the larval stage of Monarch butterflies.

Problems

No serious insect or disease problems.

Garden Uses

Sunny borders, stream/pond banks, butterfly gardens. A good plant for low spots or other moist areas in the landscape.