What is Swamp Milkweed?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 16 October 2019
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Swamp milkweed is a perennial flowering plant found in wet and damp soils like those near rivers, streams, ditches, and swamps. This plant is native to North America and is found widely distributed across this continent in addition to being grown ornamentally in many regions of the world. A number of unique cultivars have been developed for ornamental use and are available through nurseries and garden suppliers, as well as gardening exchanges.

This plant is herbaceous and short, with long, narrow leaves. The flowers are produced in umbels and in nature vary in color from mauve to white. Cultivars developed for use in gardens come in shades like red, orange, and yellow. When the flowers fade, they are replaced by long seedpods that eventually crack open explosively to release the seeds. The seeds have feathery attachments to help them float in breezes, allowing the plant to distribute itself.

Swamp milkweed grows in United States Department of Agriculture (USDA) zones three through eight. It can tolerate damp, moist, and wet soils, and has root systems specifically adapted to soils with a low oxygen content, designed to allow the plant to thrive in wet conditions. Known formally as Asclepias incarnata, this plant is very attractive to butterflies and other pollinators, thanks to the rich nectar it produces. A toxic, bitter-tasting sap in the stems is designed to repel herbivores.


People interested in growing swamp milkweed in their gardens will need a space with heavy, wet soil. The plants can be grown as specimen or massed plantings and can do well in borders and edging, where the colorful flowers will be appreciated. To prevent swamp milkweed from reseeding itself too liberally, the seed pods can be cut away as they start to develop and before they crack open to release the seeds. Seeds do not always breed true and it is important to be aware of this when harvesting seeds to plant elsewhere.

Gardeners interested in attracting birds and butterflies can use this plant, and may want to consider establishing it near a pond or pool to meet the water needs. It can be grown in full sun to partial shade and tolerates soil with poor nutrients, although it prefers soil worked with some organic material to provide a source of food. Swamp milkweed is also suitable for container gardening, although the moisture levels in the soil will have to be carefully monitored to strike a balance between drying out and drowning the roots.


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