Know Your Blooms: Swamp Milkweed

Swamp Milkweed
Have you noticed the blooms of swamp milkweed? Starting in June, swamp milkweeds flowers start opening in sunny habitats in the County, such as wet meadows and swales. This includes roadside rain gardens and bioswales where the Department of Environmental Protection (DEP) have planted the species. Swamp milkweed’s flowering hits full force in July, and then peters out in August.  
Dennis Avenue Green Streets bioswale in July

Dennis Avenue Green Streets bioswale in July

 

About Swamp Milkweed

The pink flowers of Asclepias incarnata are known as an attractant for pollinators. In particular, the plant is a food source for the monarch butterfly, both as a nectar source for the adult butterflies and as forage for the larvae caterpillars. Adult monarchs can obtain nectar from a variety of plant species. However, the larvae are specialists, feeding on only milkweeds, including butterfly weed and common milkweed. Toxins in the milkweeds provide the monarchs with some protection against predators.  
Female monarch butterfly on swamp milkweed in a Forest Estates raingarden in July

Female monarch butterfly on swamp milkweed in a Forest Estates raingarden in July

  Swamp milkweed grows about 3 feet tall and prefers to grow in full sun and moist soil. It can tolerate some light shade and drought, but of all the milkweed species, it is the least tolerant of drought. Deer don’t seem to bother it much, possibly because of the toxins in its foliage. DEP plants swamp milkweed in rain gardens, other low-impact stormwater management practices, and along pond edges.  It is a preferred plant in stormwater management, because swamp milkweed tolerates more saturated soils, and provides beauty and pollinator habitat in the summer months.  
Swamp milkweed is very attractive to pollinators.

Swamp milkweed is very attractive to pollinators.

Planting Swamp Milkweed

There are some considerations that should be taken into account when using swamp milkweed. The plants tend to be fairly sparse when not in bloom and provide minimal interest or groundcover in the cold months. For this reason, they are best combined with under-plantings, such as golden groundsel (Packera aurea) or sedge species. Also, in many locations the species has not been very long-lived. The best use for the species may be in more naturalized settings where it can self-seed or where other species can spread to take its place as the plants die out.
Bare stemmed swamp milkweed in a Dennis  Avenue Green Streets bioswale in October

Bare stemmed swamp milkweed in a Dennis Avenue Green Streets bioswale in October

 
Swamp milkweed in June, underplanted with golden groundsel in a Franklin Knolls rain garden

Swamp milkweed in June, underplanted with golden groundsel in a Franklin Knolls rain garden

 
By Darian Copiz, Watershed Planner Have a question about a plant you found in a rain garden or other stormwater management practice? Email us at askdep@montgomerycountymd.gov