swamp milkweed

Plant Type

Herbaceous Wildflower

Life Cycle

Perennial

Typical Size

4-5 ft. tall
2-3 ft. wide

Tolerant of

Deer, Occasional Flooding

Inolerant of

Dry Soil

Propagation

By seed

Plant Propagation Notes

Seed propagation notes: Cover seed with a very thin layer of soil (needs light to germinate), keep soil moist, and maintain an ambient temperature of 65-75 degrees. If you collect your own seed, to break seed dormancy either winter sow or apply cold moist stratification for 30 days prior to sowing seed.

Plant Planting Notes

Spacing: 18-36 inches.

Plants/Diseases

Oleander aphids (Aphis nerii) are a common pest of swamp milkweed. Good news: Their presence is an indicator that the plant is free of systemic pesticides! Aphid infestations can be moderated by (1) running your thumb and forefinger along the stem to squish the aphids; (2) supporting the stem with your hand and squirting it with a stream of water, since aphids have soft bodies that are easily damaged; (3) providing habitat for beneficial predators such as lady beetles and hover flies.

Wildlife Benefits

Nectar/pollen source for pollinating insects, Host plant for butterfly larvae, Nectar source for hummingbirds

Leaves

Leaves are simple, opposite, lanceolate, 3-6 inches long, 1/2 inch to 1 inch wide, with entire leaf margins, and attached to a stem by a petiole.

Flowers

Pink umbels of showy small pink flowers, approximately 20 flowers per umbel, with umbels 2-3 inches wide. The bloom period lasts approximately 1 month.

Fruit

Follicle seed pods start green and mature to brown. The pods split to release small flat brown seeds, each attached to white, fluffy hairs that function as parachutes to carry seeds in the wind away from the parent plant.

Toxicity

All parts of swamp milkweed contain cardiac glycosides and/or resinoids, with a “Low” Poison Severity rating (source: NCSU). Does not cause contact dermatitis.

Ethnobotanical Use

Stem fibers can be used for cordage.

USDA Hardiness Zones

4, 5, 6, 7, 8, 9

Light Exposure

Full Sun, Part Sun/Shade

Soil Moisture

Medium, Moist

Soil Drainage

Well-drained, Poorly Drained

Soil pH

Acidic (less than 6.0), Neutral (6.0-8.0)

Native in South Carolina?

Yes

Plant Native Habitat

Wet meadows, marshes, swamps, and margins of lakes, ponds, rivers, and streams.

Global Conservation Status (NatureServe)

Secure (G5)

Federal Conservation Status (USFWS)

Threatened

Distribution Notes

Rare in the Coastal Plain, uncommon in the Piedmont, and uncommon in the Mountains

Subspecies

There are two recognized subspecies of swamp milkweed: Asclepias incarnata ssp. pulchra (native to a strip along the eastern U.S. including SC) and Asclepias incarnata ssp. incarnata (native to the central portion of the U.S.). Distribution map from Ivey et al. 1999.