Swamp Milkweed 101 – Guide to Asclepias Incarnata


One of the most underrated perennials you can grow in your garden is Swamp Milkweed. Not only is it one of the most beautiful of all the milkweeds, it draws in tons of pollinators. Of all the milkweeds that I’ve grown over the years, Swamp Milkweed has to be the most reliable for attracting a butterflies and bees. After growing dozens of Swamp Milkweed plants over the years, I can teach you all that I’ve learned.

In this article:

What is Swamp Milkweed

Swamp Milkweed is a herbaceous long-lived perennial wildflower native to North America. Scientifically known as Asclepias Incarnata, it is host to Monarch Butterflies. Growing 3-5 feet tall in full sun and moist-to-medium soil, the lush pink blooms last for about a month and attract numerous butterflies and bees.

I grow 5-10 plants in our backyard micro-prairie. It is one of the most reliable flowers for attracting wildlife. Bees can’t seem to resist the blooms, as well as numerous species of butterflies including Black Swallowtail, Tiger Swallowtail, numerous mid-size butterflies, and of course Monarchs [1].

Swamp Milkweed Reference Table

Scientific NameAsclepias Incarnata
Common Name(s)Swamp Milkweed, Rose Milkweed, Pink Milkweed, Red Milkweed, Marsh Milkweed
Native Range, USDA ZoneEastern United States, USDA Zone 4-9
Bloom TimeJuly-August
Bloom Duration, Colors4 weeks, Pink and White
Height3-5′ (0.9m-1.5m)
Spacing / Spread18″-36″ (45 cm- 100 cm)
Light RequirementsFull sun, Partial Sun
Soil TypesLoam, Clay, Silt
MoistureMedium moisture to wet
Fauna Associations / Larval HostsHost for Monarch Butterfly. Attracts many butterflies, bees, hummingbirds.

Benefits of growing Swamp Milkweed

Swamp Milkweed is a beautiful plant! It has elegant and lush foliage with it’s dark green leaves. The pink and white blooms are exquisite and attractive, and last for about a month.

The number pollinators that you will attract by planting Swamp Milkweed is immense. If you like to see butterflies and bees in your yard, then this plant is a must-have.

Another benefit is of Swamp Milkweed is that it really is deer resistant! The foliage tastes bitter and is toxic, which keeps deer at bay. So, you get all the pollinators and none of the herbivores!

And finally, Swamp Milkweed can grow and thrive in Clay Soil! Yes, the dreaded clay soil is actually great for Swamp Milkweed. Clay soil’s ability to hold water can help keep Swamp Milkweed from drying out.

Identification / Characteristics

Swamp Milkweed can grow from 2-5′ tall depending on available sunlight. It is naturally found in prairies, swamps [2], and open areas that are not prone to drought.

Swamp Milkweed vs Common Milkweed

There are more similarities than differences when we compare Swamp Milkweed versus Common Milkweed. But, I should tell you what are the differences between Swamp Milkweed and Common Milkweed. Significant differences include where they can grow as well as height, leaves, and root characteristics.

Swamp Milkweed (Asclepias Incarnata)Common Milkweed (Asclepias Syriaca)
FlowerPink/WhitePurple / White
Seed Pods4″ long by 1/2-3/4″ diameter4″ long by 1-2″ diameter (fat pods)
Height4′3′
Leaves1″-2″ wide3″-5″ wide
RootCrown, non-aggressive rhizomesAggressive Rhizome Root (Spreads)
EnvironmentWet to Medium MoistureMedium to Dry Moisture

Stalk

Stalks of Swamp Milkweed are erect, smooth, and light green in color. They may branch near the upper third.

Swamp Milkweed Leaves

Leaves of Swamp Milkweed are 3-6″ long by 1-2″ wide, opposite along the stem and oblong to lanceolate in shape. They will be hairless and have smooth margins.

Swamp Milkweed leaves are noticeably smaller than Common Milkweed Leaves, but significantly larger than Butterfly Weed leaves. In fact leaves are one of the easiest ways to identify Swamp Milkweed prior to blooming.

Swamp Milkweed Flower

The blooms of Swamp Milkweed consist of clusters (umbels) of 10-30 individual pink/white flowers that are 2-3″ diameter. Individual flowers are approximately 6 mm diameter. They are milkweed-style flowers, having 5 petals, sepals, and hoods w/ horns.

Swamp Milkweed Bloom

The blooming period of Swamp Milkweed lasts about 4 weeks, generally starting sometime in July and ending in August. Flowers of Swamp Milkweed are some of the best smelling you can find.

Swamp Milkweed Pods

Approximately 1-2 months after blooming pods will form. The pods will be about 3 inches long by 1/2″ wide, and will contain seeds. Swamp Milkweed As these pods dry, a slit will open along the length letting seed float away with the wind.

How to grow and care for Swamp Milkweed

Swamp Milkweed sunlight requirements

Swamp Milkweed prefers full sun (6+ hours per day) to partial shade (4-6 hrs per day). The more sun available the taller and more blooms will be produced.

Soil / Moisture conditions for Swamp Milkweed

Swamp Milkweed prefers moist to medium soil, and can tolerate occasional flooding. It grows well in clay, loam, or silt.

*Not sure what kind of soil you have? Try one our or DIY Soil tests to determine your type.

Swamp Milkweed should not be grown in excessively sandy soil, without significant organic matter, as it will be too prone to drought.

Have dry soil? Maybe try it’s cousin, Butterfly Weed, which is drought tolerant.

Swamp Milkweed Care

Caring for Swamp Milkweed is very easy if you place it in conditions that it likes to grow. So, full sun and moist to medium soil and it should thrive. That being said, there are a few things you can do to keep it healthy.

Swamp Milkweed falling over

When plants start tipping over, especially native plants there a few things to investigate as to the cause. Applying fertilizer can weaken stems, and not getting full or even sun, and not getting wind from all directions can cause plants to tip over.

If Swamp Milkweed only gets sun from one direction, the plant will likely angle itself towards the sun. So, the plant will induce it’s own ‘lean’ just trying to maximize available sunlight. Also, if it is protected from wind, the stalk will be weaker. Gaining exposure to wind from all sides keeps plants stronger.

Native plants don’t need fertilizer, and applying some sort of synthetic nitrogen fertilizer can often result in taller plants with weaker stalks. So, don’t fertilize your Swamp Milkweed! You can add a small amount of compost when first transplanting, but in general they don’t need anything extra.

Swamp Milkweed Leaves turning Yellow

If you notice the entire Swamp Milkweed plant turning yellow, it may be because of herbicide. But, if you notice that it is only the lower leaves turning yellow – that is normal. Many native plants shed lower leaves when they no longer receive sun due to local competition.

If you notice Swamp Milkweed leaves drooping or wilting, you may want to check if the plant is getting enough water. This can be a sign of drought.

Swamp Milkweed in Fall / Winter

As Autumn approaches Swamp Milkweed leaves will turn red and purple. This is completely normal. It is the plants own ‘Fall Colors’ and makes for a beautiful display late in the season.

After this, the leaves will turn brown and the seed pods will open up. At this point, Swamp Milkweed can be cut back to the ground. I personally leave mine standing until Spring, as sometimes insect larvae overwinters in the stalk.

How to grow Swamp Milkweed from seed

Swamp Milkweed is relatively easy to start from seed. The seeds need to be winter sown or experience a 30 day cold moist stratification period. Subjecting Swamp Milkweed seed to cold stratification has been shown to greatly increase the germination rate [3].

Process to Grow Swamp Milkweed from seed

  1. Fill a pot, or winter-sowing container with moist potting mix
  2. Plant 3-5 Swamp Milkweed Seeds
  3. Cover with a dusting of potting soil
  4. Place container in a location that will receive morning sun and afternoon shade
  5. Germination will occur once daytime temperatures get above 70F
asclepias incarnata seedling
Swamp Milkweed Seedlings

How long does it take to establish Swamp Milkweed from seed?

In general, Swamp Milkweed will bloom the second year. If one is particularly quick in transplanting, and has fertile soil you may get lucky and be treated to a few smaller blooms the first year.

But typically, you have to wait until the second year for blooms. Here is a video I made that covers grow and care of this plant in good detail:

How to save Swamp Milkweed seed

Since I’m talking about seed, I may as well cover how to save the seed cleanly! Did you know that Swamp Milkweed is the most efficient seed producer of all milkweeds? [2] I’ve written a detailed guide on saving all milkweed seed here, but the cliff notes version is as follows:

Once pods begin to open up, gather them. Hold a pod firmly, with the bottom between your thumb and index finger, just above the seeds. Then, peel the pod like a banana.

With your other hand, begin pulling the fluff/feathers out of the pod. Don’t loosen your grip above the seeds, as we want to keep those in the pod.

Milkweed Seed Pods, Asclepias Incarnata

After several attempts, you should be able to get the central core of the feathers. Now you can just open the pod, and all of the seed should fall right out. Once fully dry, the seed can be stored for a couple of years in a sealed plastic container or envelope in a cool dry place.

Below is a short video on how to save seed from Swamp Milkweed:

Wildlife, Pests and diseases

Pollinators that visit Swamp Milkweed

Swamp Milkweed will attract numerous species of bees and pollinators. The blooms produce large amounts of nectar that attract bees, butterflies, and occasional hummingbirds.

Two Monarchs, One Swamp Milkweed……next to a swamp. How fitting!

Bees

About a dozen species of bees, wasps, and pollinating flies have been documented to visit. [4]

Butterflies

Furthermore, if you have several specimens you will likely attract large Swallowtail butterflies, Monarch butterflies, Fritillarys, and small skippers.

Caterpillars of Monarch Butterflies and Fritillarys feed on foliage as Swamp Milkweed is a larval host for them.

Other Insects that feed on Swamp Milkweed

There are an additional 32 documented insects that will feed on the foliage [5]. Some of the more prominent feeders would be milkweed aphids, tussock moths, and milkweed beetles.

Some of these insects, such as Tussock Moths, aphids, and milkweed beetles can be considered pests to gardeners. However, they do serve as part of the food chain. Birds will come eat Tussock Moths, and other bugs will eat milkweed beetles. Finally, ladybugs will come eat the aphids – although they will never completely eliminate the aphid population.

Tussock Moths

An irregular visitor is Tussock Moths. Tussock Moths will defoliate milkweeds quickly. In my experience, the plant will come back the following year. Or, birds may eat all the Tussock Moths before they have completely defoliated them.

Tussock Moth

Milkweed Beetles

Milkweed Beetles will eat the seeds of Swamp Milkweed. If you want to save seed from your plants, then you should make sure you remove and discard pods that become infested with Milkweed Beetles.

A milkweed beetle feeding frenzy

Swamp Milkweed beetles will lay their eggs on the leaf, and look like small orange capsules.

Yellow aphids

Orange or yellow bugs (aphids, Aphis nerii) will frequently find their way to Swamp Milkweed plants. They are very tiny, perhaps 1/16″ (1.5 mm) diameter. They suck the sap from the stems.

Milkweed aphids
Yellow/Orange Milkweed Aphids

In my experience, they don’t harm the plant very much. I generally don’t even try to control them, as they don’t seem to effect the flowering. But if you wish to control aphids, you have three options:

  1. Spray them off with a hose
  2. Spray them with soapy water.
  3. Squish them with your fingers.

Deer and Rabbits and Swamp Milkweed

Swamp milkweed is deer and rabbit resistant. The leaves and stem are bitter, making them unpalatable. Although, as with most seedlings, I’ve found rabbits to eat young tender seedlings. But once a plant reaches 12″ or more, they are left alone in my experience.

Swamp Milkweed and Dogs

In regards to toxicity, Swamp Milkweed is toxic to all mammals in large quantities. And this includes dogs [8], as well as sheep, cattle, poultry, and horses. [7]

Swamp Milkweed Fungus

Like most plants, Swamp Milkweed can be victim of the occasional fungus attack. If you happen to observe leaves of Swamp Milkweed with brown or dark spots, it is likely some form of leaf-spot fungus.

I do not recommend you spray your plants if they are preparing to bloom, or anytime after. Just remove the affected leaves and try to promote more air flow through the plants.

Spraying fungicide could have negative or fatal effects on Monarch caterpillars. So, that is why you should avoid spraying the leaves. Removing the leaves with brown spots on Swamp Milkweed is the safest course of action. As the disease is primarily cosmetic.

Where to buy Swamp Milkweed

Swamp Milkweed is generally not found in stores. It is best to purchase seed, or gather seed from the wild. Then, just grow your own plants!

Purchase Seed

We have ordered a variety of native flower seeds from Everwilde Farms, which you can order right from Amazon through our link on our RECOMMENDED PRODUCTS PAGE. (We may earn a small commission when you purchase through our links, at no cost to you. This helps support our website.)

Swamp Milkweed Uses

Garden Uses of Swamp Milkweed

Being quite showy, Swamp Milkweed can do great in a formal flowerbed. It does not spread far and wide like its cousin, Common Milkweed. Although local self-seeding does occur. You will be treated to a clump of plants, and this is desirable.

Swamp Milkweed asclepias incarnata

The more plants you have packed closer together, the more likely you are to attract lots of butterflies and other pollinators. Furthermore, the closer the plants are together, the fewer weeds you will have growing as the plants will shade them out.

But Swamp Milkweed does great near water, ditches, ponds, or any rain garden. The key thing is having soil that is either moist, or can hold moisture well.

Swamp Milkweed Companion Plants

Swamp Milkweed pairs well with any moisture loving plant that thrives in full sun. Some great companion plants that have overlapping bloom times include the following:

In fact, Joe Pye Weed and Swamp Milkweed can often be confused! The primary difference between Joe Pye Weed and Swamp Milkweed is the bloom and leaves.

Native American Uses for Swamp Milkweed

*Note that Milkweed is toxic and should not be consumed.

There are over 20 uses of Swamp Milkweed documented by 4 different tribes. The Chippewa, Meskwaki, and Cherokee tribes primarily used Swamp Milkweed as a drug to treat various ailments. Some of the ways it was used was as a diuretic, emetic, cathartic and for pediatric or kidney issues, as well as man other uses. [6]

The Menominee would use the seed heads as food during winter. Also to make soups.

Fibers

The fibers of Swamp Milkweed stalks can be used to make rope/cordage and woven into cloth.  As with Common Milkweed, wait until the stalks are brown/dry and can be broken off at the base.  Once dry, remove the outer layer by hand, then weave the fibers into a cloth.  Or, you can twist the fibers opposite to make rope.

Feather/parachute Uses

A really interesting use for Swamp Milkweed was that it helped the Allies win World War II!  The parachutes that are attached to each seed in the seed pods were used in World War Two to fill life jackets for the Allies.  This is because the feathery parachutes are much more buoyant than cork and other materials.  Additionally, the feathers can be used to stuff pillows, as they are quite soft.

Click Here to read about other milkweeds

References:

[1] – Luna, T., & Dumroese, R. K. (2013). Monarchs (Danaus plexippus) and milkweeds (Asclepias species): The current situation and methods for propagating milkweeds. Native Plants Journal, 14(1), 5–15. http://doi.org/10.1353/npj.2013.0006

[2] – Wilbur, Henry M. “Life History Evolution in Seven Milkweeds of the Genus Asclepias.” Journal of Ecology, vol. 64, no. 1, 1976, pp. 223–240. JSTOR, www.jstor.org/stable/2258693. Accessed 11 Feb. 2021.

[3] – Population, Temperature, and Substrate Influences on Common Milkweed (Asclepias syriaca) Seed Germination. Farmer, Price, and Bell. Weed Science, Vol.34, No. 4.

[4] – Ivey, C.T., Martinez, P. and Wyatt, R. (2003), Variation in pollinator effectiveness in swamp milkweed, Asclepias incarnata (Apocynaceae). Am. J. Bot., 90: 214-225. https://doi.org/10.3732/ajb.90.2.214

[5] – Betz, Rommel, Dichtl. Insect Herbivores of 12 Milkweed (Asclepias) Species. Department of Biology, Northeastern Illinois University. 1997. www.plantconservation.us/BetzRommel.pdf Retrieved 11FEB2021.

[6] – Swamp Milkweed. Native American Ethnobotany Database. http://naeb.brit.org/uses/species/434/ Retrieved 11FEB2021.

[7] – Brotherson, Jack D., et al. “POISONOUS PLANTS OF UTAH.” The Great Basin Naturalist, vol. 40, no. 3, 1980, pp. 229–253. JSTOR, www.jstor.org/stable/41711890. Accessed 23 Feb. 2021.

[8] – Toxic and Non-Toxic plants to Dogs, ASPCA, https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/milkweed Retrieved 15FEB2021.

Joe Foster

Hi - I grew up outdoors in nature - hiking, fishing, hunting. In high school I got my first job at a garden center where I learned to garden and landscape. I've been growing plants from seed and designing native plant gardens for over six years. I hope to share some of my knowledge with you! Additionally I am a wood worker / DIY enthusiast. I enjoy designing/building projects (with hand tools when I can!). I hope to give you some tips and useful information!

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