How to grow swamp milkweed?

Contents

Plant of the Week

Range map of swamp milkweed. States are colored green where the species may be found.

Swamp milkweed with Monarch caterpillar. Photo courtesy of Jennifer Anderson, USDA-NRCS PLANTS Database.

Swamp milkweed (Asclepias incarnata) with paper wasp. Photo courtesy of Linda R. Parker, U.S. Forest Service.

Swamp Milkweed (Asclepias incarnata L.)

By Forest Russell Holmes

Swamp milkweed, Asclepias incarnata, is named for the Greek god of medicine, Asklepios. Incarnata, is from the Latin carn, meaning flesh and atus, like, because its hue is sometimes like flesh or dusty rose in color.

As a tall herbaceous moisture-loving perennial, Swamp milkweed seeks sunny openings of swamps, marshes, bogs, fens, and open areas along stream banks and ditches. This robust and erect stemmed plant grows three to five feet high, and like its common milkweed cousin, exudes a milky juice when broken.

Swamp milkweed’s smooth narrow leaves are lance-shaped with sharp tips and occur in pairs. Sometimes the leaf’s edges turn inward and upward suggesting the prow of a ship.

The fragrant umbelled clusters of flowers range in color from soft mauve to pink to reddish-violet. Five tiny delicate petals are crowned with five nectar cups that are crucial in its intricate pollination. Within each small cup is an upward curving horn. An insect landing on the blossom slips on the horn. Its leg goes into a slit between the cups and picks up pollen. The same process is repeated as it visits other blossoms. Carrying its pollinia like large saddlebags, it then deposits them to fertilize other plants (sometimes insects are not strong enough to pull their feet out of the slits and they are trapped there and die). The fruit/seeds of the milkweed are attached to silky down and are encased in long one-chambered follicles, pods really, quite elegant in appearance. When the follicles dry, they split open, releasing the seeds with their downy parachutes to the wind.

Swamp milkweed attracts a profusion of butterflies, especially the monarch butterfly. Besides nectaring the monarch butterfly only lays it eggs on milkweeds. It will thrive in average garden soil as long as it does not dry out completely, especially in the spring. Thus, it is an excellent addition to a native plant garden.

For More Information

  • PLANTS Profile – Asclepias incarnata, swamp milkweed
  • Gardening with Wildflowers
  • See other Plant of the Week Asclepias species…
  • Monarch Butterfly: Habitat Needs

Asclepias Species, Swamp Milkweed, Rose Milkweed, Swamp Silkweed

View this plant in a garden

Category:

Perennials

Water Requirements:

Requires consistently moist soil; do not let dry out between waterings

Sun Exposure:

Sun to Partial Shade

Foliage:

Herbaceous

Foliage Color:

Unknown – Tell us

Height:

24-36 in. (60-90 cm)

36-48 in. (90-120 cm)

4-6 ft. (1.2-1.8 m)

Spacing:

24-36 in. (60-90 cm)

Hardiness:

USDA Zone 3a: to -39.9 °C (-40 °F)

USDA Zone 3b: to -37.2 °C (-35 °F)

USDA Zone 4a: to -34.4 °C (-30 °F)

USDA Zone 4b: to -31.6 °C (-25 °F)

USDA Zone 5a: to -28.8 °C (-20 °F)

USDA Zone 5b: to -26.1 °C (-15 °F)

USDA Zone 6a: to -23.3 °C (-10 °F)

USDA Zone 6b: to -20.5 °C (-5 °F)

USDA Zone 7a: to -17.7 °C (0 °F)

USDA Zone 7b: to -14.9 °C (5 °F)

USDA Zone 8a: to -12.2 °C (10 °F)

USDA Zone 8b: to -9.4 °C (15 °F)

Where to Grow:

Grow outdoors year-round in hardiness zone

Danger:

All parts of plant are poisonous if ingested

Bloom Color:

Pink

Medium Purple

Bloom Characteristics:

This plant is attractive to bees, butterflies and/or birds

Bloom Size:

Unknown – Tell us

Bloom Time:

Mid Summer

Late Summer/Early Fall

Other details:

Unknown – Tell us

Soil pH requirements:

5.6 to 6.0 (acidic)

6.1 to 6.5 (mildly acidic)

6.6 to 7.5 (neutral)

Patent Information:

Non-patented

Propagation Methods:

By dividing rhizomes, tubers, corms or bulbs (including offsets)

From seed; direct sow outdoors in fall

From seed; winter sow in vented containers, coldframe or unheated greenhouse

From seed; stratify if sowing indoors

Seed Collecting:

Bag seedheads to capture ripening seed

Allow pods to dry on plant; break open to collect seeds

Properly cleaned, seed can be successfully stored

Regional

This plant has been said to grow in the following regions:

Elmore, Alabama

Mabelvale, Arkansas

North Little Rock, Arkansas

Sacramento, California

Kiowa, Colorado

Littleton, Colorado

Dover, Delaware

Fort Lauderdale, Florida

Gibsonton, Florida

Loxahatchee, Florida

Lutz, Florida

Saint Cloud, Florida

Sarasota, Florida

Bogart, Georgia

Demorest, Georgia

Marietta, Georgia

Anna, Illinois

Cherry Valley, Illinois

Crest Hill, Illinois

Crystal Lake, Illinois

Divernon, Illinois

Edwardsville, Illinois

Evanston, Illinois

Itasca, Illinois

La Grange Park, Illinois

Machesney Park, Illinois

Mount Prospect, Illinois

Springfield, Illinois

Thomasboro, Illinois

Greenville, Indiana

Indianapolis, Indiana

Washington, Indiana

Ames, Iowa

Iowa City, Iowa

Yale, Iowa

Brookville, Kansas

Derby, Kansas

Hiawatha, Kansas

Barbourville, Kentucky

Prospect, Kentucky

New Orleans, Louisiana

Slidell, Louisiana

Brookeville, Maryland

Dundalk, Maryland

Springfield, Massachusetts

Allen Park, Michigan

Barton City, Michigan

Dearborn Heights, Michigan

East Tawas, Michigan

Grand Rapids, Michigan

Kasota, Minnesota

Minneapolis, Minnesota(2 reports)

Onamia, Minnesota

Pequot Lakes, Minnesota

Saint Paul, Minnesota

Young America, Minnesota

Kansas City, Missouri

Saint Louis, Missouri

Helena, Montana

Beatrice, Nebraska

Lincoln, Nebraska

Frenchtown, New Jersey

Jersey City, New Jersey

Morristown, New Jersey

Mount Laurel, New Jersey

Westwood, New Jersey

Elephant Butte, New Mexico

Blossvale, New York

Brooklyn, New York

Ogdensburg, New York

Charlotte, North Carolina

Hays, North Carolina

Tobaccoville, North Carolina

Fargo, North Dakota

Bowling Green, Ohio

Columbus, Ohio

Dayton, Ohio(2 reports)

Fairborn, Ohio

Findlay, Ohio

Fort Jennings, Ohio

Glouster, Ohio

Napoleon, Ohio

Oak Harbor, Ohio

Saint Marys, Ohio

Springboro, Ohio

Portland, Oregon

Malvern, Pennsylvania

Milford, Pennsylvania

Norristown, Pennsylvania

Philadelphia, Pennsylvania

Waynesboro, Pennsylvania

West Chester, Pennsylvania

Wilkes Barre, Pennsylvania

Conway, South Carolina

Okatie, South Carolina

Rock Hill, South Carolina

Parker, South Dakota

Viola, Tennessee

Belton, Texas

Fort Worth, Texas

Los Fresnos, Texas

Salt Lake City, Utah

Arlington, Virginia

Leesburg, Virginia

Manassas, Virginia

Mc Lean, Virginia

Newport News, Virginia

Portsmouth, Virginia

Sterling, Virginia

Orchards, Washington

Spokane, Washington

Berkeley Springs, West Virginia

Cabin Creek, West Virginia

Liberty, West Virginia

De Pere, Wisconsin

Madison, Wisconsin

Milwaukee, Wisconsin

show all

Swamp milkweed

Size

2 to 5 feet high and 2 to 3 feet wide

Tree & Plant Care

Requires full sun in moist to wet soil, can tolerate well drained soils.
Foliage is slow to emerge in spring.
Plants have deep taproots and difficult to transplant.

Disease, pests and problems

Milkweed bugs and milkweed beetle are late season pests.

Disease, pest and problem resistance

Deer, rabbit

Native geographic location and habitat

C-Value: 4
Commonly found in swampy areas and wet meadows.

Attracts birds & butterflies

Small rosy-pink flowers is a great nectar source for many butterflies and leaves are the larval host for the monarch butterfly.

Leaf or needle arrangement, size, shape, and texture

Opposite, 3 to 6 inches long, lance shaped with pointed tips

Flower arrangement, shape, and size

Small, fragrant, pink to mauve flowers (1/4 inch wide), with five reflexed petals in a loose umbels at the stem ends in summer.
Said to smell like vanilla scent.

Fruit, cone, nut, and seed descriptions

Long, 4 to 5 inch green seed pods (follicles) split and release light to dark brown seeds attached to silver-white silky hairs.

Swamp Milkweed Info – Tips For Growing Swamp Milkweed Plants

A cousin of the better-known common milkweed, swamp milkweed is an attractive flowering perennial that is native to the swamps and other wet areas of North America. Keep reading to learn more swamp milkweed info, including swamp milkweed benefits and tips for growing swamp milkweed in your landscape.

Swamp Milkweed Info

What is swamp milkweed? Swamp milkweed (Asclepias incarnata) is a member of the milkweed family. It is thought to have earned its name from the pink flowers it produces (“Incarnata” means “flushed with pink.”) It produces these flowers in midsummer, followed by narrow seed pods that open to reveal flat brown seeds attached to the classic white tufts associated with milkweed plants.

The flowers are very showy and good for attracting butterflies. The plants tend to reach 2 to 4 feet (.60 to 1.2 m.) in height. Swamp milkweed plants can be distinguished from their other milkweed cousins both by these showy pink flowers and by their habitat, as they are the only species of milkweed that prefer to grow in wet conditions.

Growing Swamp Milkweed

Swamp milkweed, as the name suggests, grows best in moist, wetland areas. It likes wet, clay soil, but it also prefers full sun. The plant is hardy in USDA zones 3 through 6, where it grows as a perennial. The plants spread naturally by wind-borne seeds and by creeping roots that spread out slowly under the ground.

Should I Grow Swamp Milkweed?

The swamp milkweed plant is technically poisonous to humans and other mammals if enough of it is eaten, so it should be avoided in areas where children play or livestock forage. It is, however, a good attractor for pollinators and a North American native, so it is a good choice for gardeners with wet sites on their property who are looking to plant responsibly.

How We Collect and Process Milkweed Seeds for Monarchs

How does the U.S. Fish and Wildlife Service (Service) help monarchs on their epic journey? Enter, the National Wildlife Refuge System. The National Wildlife Refuge System is the largest and most diverse network of lands and waters. Think lots of wildlife, clean water, clear air, gorgeous landscapes, and world-class recreation.

Within the National Wildlife Refuge System are Wetland Management Districts, little known but very important components of the system.

Within the Districts, small parcels of land called Waterfowl Production Areas are purchased and managed by the Service to provide nesting habitat for waterfowl. But, that’s not all they do. The Waterfowl Production Areas provide vital habitat for monarch butterflies and other pollinators. Their diversity of native grasses and flowers, along with milkweed, provide the food and shelter migrating monarch butterflies need.

Milkweed is the host plant for monarch butterflies and the only source of food for monarch caterpillars. Unfortunately, monarch populations are in decline because milkweed is disappearing from the American landscape due to habitat loss, pesticide use, development, and shifts in climate patterns. The Districts are stepping up and doing their part to help this iconic insect.

Each fall, the Madison Wetland Management District and Lake Andes Wetland Management District in South Dakota collect and process milkweed seeds. There are more than 100 different milkweed species native to North America, but Madison and Lakes Andes collect common milkweed (Asclepias syriaca).

Asclepias

Meadows are one of my favorite places to be, largely because of the lovely milkweed that I often find there.

Tall and topped with sprays of flowers, an arrow-straight stem with funky looking oval leaves, and crawling with caterpillars, beetles, and butterflies? Yeah, that’s the plant for me.

You’re probably familiar with the common milkweed seen in meadows and roadsides across the country, but the milkweed family is actually huge. We’re going to take a look at some different cultivars used in gardens, and learn how to grow this plant.

Photo by Matt Suwak.

More important than that, though, we’re going to talk about the importance of milkweed in the environment. Here’s what’s ahead in this article

Buckle in, we’re going to get started.

Start with the Basics

Milkweed is botanically known as Asclepias spp. and has over one hundred known species. It was named by Carl Linnaeus after the Greek god of healing, Asclepius, and the species is native to the Americas.

This nod to a god of healing is because of the use of the sap as a medicinal aid, namely for dysentery and warts, by the native people in the Americas.

While the milky white latex inside the stems is often toxic, the rest of the fibers in the plant have earned Asclepias the nickname “Silk of America.” These fibers have been used for insulation and cleaning oil spills, and can be found in some hypoallergenic pillows.

But most of us know the value of milkweed because of its necessity in the life cycle of the monarch butterfly.

The Milkweed and the Butterfly

As a kid, I remember learning that milkweed sap is toxic. But monarch caterpillars can eat Asclepias safely and then become toxic to predators later on in their life cycle.

Our teacher went into the meadow outside of the school, found a monarch caterpillar on a piece of milkweed, and brought it in to show us.

Photo by Matt Suwak.

Hoards of children watched the chrysalis formation and waited impatiently for the butterfly to molt. It did, eventually… over the weekend, when nobody was around!

Our teacher said she released it into the wild to prevent it from being cooped up for too long.

Photo by Matt Suwak.

I don’t know if the thing simply died and she didn’t want to break our tiny 7-year-old hearts, but I do know that the lessons she taught about the natural dynamic of milkweed and butterfly stuck with me for the rest of my life.

How Integral Is this Relationship?

In a word: it’s absolutely integral!

Monarch caterpillars utterly depend on Asclepias for their diet, but so too do a number of insects all specialized in dining on the otherwise-toxic milky sap of the plant.

A monarch butterfly will lay its eggs on the underside of a leaf. In fact, this is the only place where a monarch will lay its eggs.

When the eggs hatch, the tiny caterpillars start going to town, and chomp down on the Asclepias.

Amazingly, the plants have built-in defenses like irritating hairs and their aforementioned natural toxins to slow the buffet line down, but they do not altogether prevent the insects from using the plant as a food source.

Most monarchs live for an average of 4 weeks, but every fourth generation lives for 6 to 8 months! This is the generation that will complete an incredible flight to the southern regions of North America, to roost and overwinter before continuing the journey northward to start the cycle anew.

This plant is also a primary food source and shelter for a variety of beetles, and has earned its place as a vital native plant species for healthy ecosystems nationwide.

The Butterfly Garden

The popularity of butterfly gardens was spurred in a big way because of the plight of the monarch, and this style of garden has attracted plenty of folks to the realm of gardening. That makes me love butterfly gardens!

Asclepias and other native flowers like black-eyed susans, echinacea, joe pye weed, sweet alyssum, and sunflowers are some of the easy-to-grow plants that may make up a successful butterfly garden.

All butterflies are pollinators and are attracted to this style of flower. Plant the right types, and you’ll have a never-ending summer show of cascading butterflies!

The biggest benefit of a healthy butterfly garden is that it strengthens the rest of your local ecosystem. When butterflies are present, that means birds, bats, and other critters that feed on butterflies are able to make a resurgence as well.

Photo by Matt Suwak.

Think of a butterfly garden, and milkweed’s place in it, as an essential strand in the food web!

Ideal Planting Conditions and Potential Problems

Despite sharing a name, many milkweed types require different growing conditions. Some prefer hot and dry areas while others thrive only in moist conditions, but they all need ample sunlight to do their best.

The common milkweed does well in what might be considered average conditions: moderately dry and well-draining soil, no special fertilizers or nutrition requirements, and about 8 hours of sun a day.

Most of the species I’ve worked with prefer that “average” blend of characteristics. These plants can be plopped into the garden and be given a springtime coating of compost, then be on their way to growing lovely and stunning flowers.

Most don’t require any extra watering except during the hottest dry spells.

Because of their toxicity, Asclepias also attracts few ailments or problems.

Besides typical fungal issues that can be found in many areas of the garden with an abundance of moisture, milkweed can suffer from general heat stress and damage. Remove yellowed leaves and those with lots of damage from insects.

Mites can become a problem, but any general insecticidal treatment works; just be careful not to poison those desirable insects, as well!

Milkweed yellows phytoplasma is a more serious issue identified by malformed, yellowish growth and branch dieback. The only solution here is to remove and destroy the infected plants before they spread the ailment to other plants.

To avoid these conditions, keep your plants thinned out and avoid standing pools of water and over-watering in general. Milkweed would rather be too dry than too wet!

How to Start Growing Your Own (and Where to Buy Them)

Many garden centers will sell a variety of milkweed species during the growing season, but finding live plants online can be difficult. That’s because, for all of their toughness to natural predators and tolerance of growing conditions, Asclepias can be very sensitive to transplanting and handling.

For that reason, I recommend starting yours from seed. Fortunately for those who really like to do it all yourself, milkweed plants produce extraordinarily generous bounties of seeds for you to harvest.

Each individual seed pod can contain a hundred or more seeds, and plants have multiple seed pods each!

I usually collect my seeds from the gardens of friends and clients, but I’ve snagged a single pod or two when out hiking as well.

Asclepias seeds need a period of cold to become viable, with some added moisture. This process is called “cold stratification,” and you’ve got two easy options for how to accomplish this task:

1. Chill Manually

Place your seeds on a damp paper towel and plop them into a ziplock bag.

Label the bag with the date, and keep it somewhere in your refrigerator where it won’t be bothered; you need to leave the seeds largely undisturbed for about thirty days before they become viable.

After stratifying, you can start your seeds in a growing medium about three to four weeks before the last freeze date.

2. Direct Sow in Cool Climates

Directly sow your seeds in the garden in the late fall, and let the winter weather take care of cold stratification for you!

If you’re cold stratifying the seeds yourself…

  • Start the seeds, preferably in peat pods.
  • After wetting and preparing the growing medium, add one to three seeds per pod. If you use more than one seed you’ll have better luck that at least one will grow, but you’ll need to thin out the weaker seedlings.
  • Layer about 1/4” of soil onto the seeds and keep them in a warm area with lots of light.
  • Be very careful when moving and planting your Asclepias seedlings; they are very fragile and need delicate care.
  • Plant the pods directly into the garden before the plants reach about 3” in height to avoid damaging the sensitive taproot, and wait until after the last freeze date before planting.
  • Ensure the top of the peat pods is covered in soil, or carefully cut any extra pieces away to prevent the peat from stealing moisture from the seedling.

All of these steps can be skipped if you’re sowing the seeds outdoors, but I would recommend planting lots of extra seeds if you take this route. You can thin them out later as the season goes on, and this helps to avoid the frustrating experience of having none of the seeds germinate because you sowed too sparsely.

100 A. Syriaca Open Pollinated Seeds, available via Amazon

If you want to plant the common milkweed (A. syriaca), this is a good bunch of seeds! Common milkweed grows in zones 4-9, and reaches a height of about three feet. It’s the plant we’re most familiar with seeing growing in the wild.

100 A. Incarnata Open Pollinated Seeds, available on Amazon

For the swamp milkweed (A. incarnata), these seeds receive consistently good reviews, and are sold via Seed Needs USA. The swamp variety of Asclepias will grow in zones 3-9 and can reach a height of five feet tall!

50 Whorled Milkweed Seeds from Zellajake Farm, available via Amazon

The whorled milkweed (A. verticillata) is a lovely plant for those who want something a bit more shy (reaching about two feet tall max) that grows in zones 4-9. These seeds are from a reliable grower and have good germination rates.

Heirloom Bloodflower Seeds, available from Eden Brothers

Want to add a splash of dazzling color to your flower beds? The bloodflower, or sunset flower (A. curassavica) is another stunning variety, with red and yellow flowers and a max height of about 36 inches. This variety is recommended for zones 3-9.

A. Tuberosa Seeds, available from Eden Brothers

The aptly named butterfly weed (A. tuberosa) is another colorful variety, with vibrant orange flowers. It will grow to a height of 24-36 inches in zones 3-9.

Most of these companies recommend cold stratifying the seeds before spring planting to further guarantee germination, so order early! Otherwise, they’re ready to go if you sow outdoor in the fall.

A. Incarnata Ice Ballet Plant in #2 Container, available from Nature Hills

If you REALLY want a live plant, I recommend ‘Ice Ballet.’ It grows to reach about two to three feet in height and has a lovely shade of white to its flowers. I’ve seen it in a few select gardens, and I wish I saw it in more because this plant is a real beauty.

Get Planting and Attract Those Butterflies!

While they are sensitive and require special handling when young, Asclepias become hardy and easy to care for within a few weeks. Better yet, they attract a veritable swarm of wildlife, and that’s always a good thing for the eco-conscious gardener!

Asclepias are at their best when they’re given room to grow and do what they want to do, but with the right attention, they can shine in even the most well-manicured garden. The beetles, the butterflies, and the pollinators will all thank you for giving this iconic American perennial a shot in your garden!

Do you have some extra tips on growing milkweed to share, or maybe a few questions? Please drop us a line in the comments below. Thanks for reading, and check back soon!

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Photos by Matt Suwak © Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product photos via Nature Hills, Zellajake Farm and Garden, Seed Needs, and Eden Brothers.

About Matt Suwak

Matt Suwak was reared by the bear and the bobcat and the coyote of rural Pennsylvania. This upbringing keeps him permanently affixed to the outdoors where most of his personal time is invested in gardening, bird watching, and hiking. He presently resides in Philadelphia and works under the sun as a landscaper and gardener, and by moonlight as a writer. An incessant questioning of “Why?” affords him countless opportunities to ponder the (in)significance of the great and the small. He considers folksy adages priceless treasures and is fueled almost entirely by beer and hot sauce.

CHECK AVAILABILITY

FIRST IMPRESSIONS: This elegant plant is upright with slender willow like leaves. In summer plants are topped by clear white flower clusters which attract flocks of butterflies. Plants thrive in sunny sites with moist or saturated soils. The ‘Ice Ballet’ cultivar differs from the species due to its white flowers, more compact habit and darker green foliage.

HABITAT & HARDINESS: ‘Asclepias incarnata ‘Ice Ballet’ is a nursery selection of the native Swamp Milkweed so it does not exist in the wild.

Plants are hardy from USDA Zones 3-9.

PLANT DESCRIPTION: This Swamp Milkweed cultivar is an erect clump forming perennial that grows from a taproot.

Plants have narrow lance shaped leaves with pointed tips and smooth margins. Stems and leaves contain a milky sap that exudes when plants are damaged. Desirable yellow and black Monarch caterpillars feed on the foliage.

Fragrant summer umbels are composed of many tiny star shaped florets. The intricate florets look like freshly extruded white cake decorations. Butterflies, bees and moths seek the floral nectar.

After flowering 4” seed pods split and release brown seed with silken parachutes that drift away on the wind.

Plants are more compact than the species growing about 3’ tall with 2-3’ spread.

CULTURAL & MAINTENANCE NEEDS: Asclepias incarnata ‘Ice Ballet’ is a sun loving plant for moist or saturated soils.

It is almost impossible to grow milkweed without a throng of oleander aphids in residence. These tiny orange plant lice suck the plant’s sugary sap and exude sticky honeydew that is the perfect cultural medium for black sooty mold. All phases and consequences of the oleander aphid life cycle are alarming to gardeners. The actual damage to the plant, however, is usually minimal and no treatment is needed.

Milkweeds are not palatable to deer, rabbits and other herbivores.

LANDSCAPE USES: Asclepias incarnata ‘Ice Ballet’ is a great choice for a well drained Perennial Border or a garden with a difficult sunny wet microclimate. Plants are also used as an Accent, Butterfly Nectar Plant, Butterfly Host Plant or as part of a Grouping or Mass Planting. It provides Fragrance and Showy Blooms and is useful in Cottage Gardens, Deer Resistant Plantings and Low Maintenance Plantings.

COMPANION & UNDERSTUDY PLANTS: Asclepias incarnata ‘Ice Ballet’ mingles well with other sun & moisture lovers like Eupatorium fistulosum, Lobelia cardinalis, Helianthus angustifolia, Eupatorium colestinum and Aster novae-angliae.

The Asclepias incarnata species can be substituted if needed.

TRIVIA: Milkweed sap contains bitter tasting and toxic cardiac glycosides. These chemicals accumulate in the bodies of Monarch caterpillars and function as a safeguard against predators. High toxin concentrations make the caterpillar more poisonous and impart more protection. Usually Monarch caterpillars and other milkweed foragers develop a bright warning color that may be interpreted as “If you eat me, you’ll die!”

All sorts of undesirable bugs (like the oleander aphid) love the milkweeds. If this is an issue, conventional pesticide treatments should be avoided because they will usually kill the highly desirable Monarch Butterfly caterpillar.

Swamp Milkweed Seeds

Plant Swamp Milkweed Seeds for Monarchs

Asclepias incarnata Native Plant Range
USDA, NRCS. 2016. The PLANTS Database (http://plants.usda.gov)

Asclepias incarnata is well know as Swamp milkweed and is one of the milkweeds that are usually highly preferred by the Monarch butterflies. Other common names include Rose Milkweed, Rose Milkflower, or Swamp Silkseed. Adult female Monarchs will readily lay their eggs on this plant. Queen butterflies may also use Swamp milkweed as a host plant.

As well as being a host plant, Asclepias incarnata is also a great nectar source and attracts many other kinds of butterflies.

Swamp Milkweed Overview

Asclepias incarnata is a native perennial milkweed to the most of the US and Eastern Canada and is hardy from USDA zones 3 to 8. Only the far western states of the US fall outside of the native region.

A Monarch butterfly is laying
an egg on swamp milkweed
Source: Paulinehorn24reproduced
under Creative Commons

This milkweed has fragrant clusters of small flowers that are loved by many butterfly species besides just the Monarchs. Swamp milkweed will flower the first summer from seed and like many milkweeds will flower all summer.

Unlike some other milkweeds (such as Common milkweed and Showy milkweed), Swamp milkweed is well behaved in the garden and will grow in clumps rather than invasively spreading around with far-reaching underground rhizomes. It is a common addition to butterfly gardens as it is useful and pretty at the same time.

Swamp milkweed can vary greatly in height anywhere from 2-6 ft but is probably most commonly seen around 3-4 ft tall. They will die back in the fall to return from the ground in the spring.

A Monarch caterpillar is munching
on Asclepias Incarnata
Source: Paulinehorn24 reproduced under Creative Commons

Another great thing about Swamp milkweed is that like many of the milkweeds it is very attractive to many species of butterflies as a nectar source. So not only will it draw the Monarchs for nectar and hosting, it is a general butterfly magnet.

How to Grow Asclepias Incarnata

As its name suggests, Swamp milkweed is most often found growing in rich moist areas like marshes or near streams in its native setting. It is tolerant of wet clay soils and areas without good drainage.

A Clump of Swamp Milkweed
Source: intheburg reproduced under
Creative Commons

However, once established it will do quite well in average gardens. Keep it well watered until it is established then water it as you would for any of your plants that require average-moist garden conditions. Some people actually report that it will tolerate dry conditions. However, for hot and dry conditions you may want to consider other Milkweeds such as Butterfly Weed.

Swamp milkweed will grow in full sun or part shade.

Germinating Swamp Milkweed Seeds

Like most milkweeds, Swamp milkweed is most commonly grown from seed rather than cuttings. Asclepias incarnata requires at least 30 days of cold stratification before it will germinate. Cold stratification is the process of exposing the seed to cold and moist conditions to break dormancy.

You can allow nature to cold stratify the seeds for you by planting them outdoors in the Fall or using winter-sowing techniques. Or you can cold-stratify indoors by placing the seeds in moist sand, moist vermiculite, moist coffee filter, etc, in a resealable plastic bag in the refrigerator. There is a lot of information online about cold-stratification if you would like to research it further.

When sowing Swamp Milkweed seeds, barely cover the seed with soil and keep the soil moist and in bright light because light can help with germination. The seeds should germinate within 1-3 weeks.

Swamp Milkweed Seed Pod
Source: Flatbush Gardener
reproduced under Creative Commons

Swamp milkweed produces plenty of seed for you to share or start new plants. Collect the seed in late summer/fall just as the elongated seed pod is starting to split open but before the white “fluff” starts to float out. At this stage it is pretty easy to strip the seeds off the white silky threads that will soon fluff up and allow the seed to float off in the wind.

Consider Buying Asclepias incarnata Seeds and Plants

Swamp milkweed is one of the Monarchs favorite milkweeds and is treasured by many butterfly gardeners as a Monarch butterfly host plant due to its beauty, fragrance, attractiveness to many butterflies and “good behavior” in the garden (not invasive). We have other Milkweeds you may want to consider as well. Also, we have an article about raising Monarchs if you would like more information about the Monarch butterfly.

Family:

Milkweed Family (Asclepiadaceae)

Other Names:

flesh-colored milkweed, rabbit milk, rose milkweed, rose silkweed, silkplant, swamp silkweed, water nerve root, white Indian hemp.

Origin and Distribution:

Swamp milkweed is a native of North America. It is currently distributed throughout Ohio in marshes, swamps, fens, ditches, open woods, wet prairies, fields, thickets, and shores. Swamp milkweed prefers moist sites.

Plant Description:

Swamp milkweed is a slender perennial. Its stems and leaves exude a white milky sap if cut or broken, which is a common characteristic of species in the Milkweed Family. It can be distinguished from other milkweeds by its habitat, as it is the only native milkweed species preferring wet ground. Reproduction is by way of seeds and weakly creeping roots.

  • Root System:

    Roots about 1 inch in diameter, knotty, and surrounded by rootlets and creeping roots.

  • Seedlings and Shoots:

    Stems of young plants are purple-tinged and their leaves have short hairs around the edges and on the prominent midveins located on the lower surface.

  • Stems:

    Stems emerge either alone or in clusters from a single root crown. Stems are generally upright, 1 to 4 feet tall, hairy, leafy, undivided at the base, and branched at the top.

  • Leaves:

    Leaves are opposite (2 leaves per node), 2 to 8 inches long, no more than 1 1/2 inches wide, numerous, and lance-shaped. Upper and lower leaf surfaces are usually hairless. Veins are clearly visible on the lower surface of the leaf.

  • Flowers:

    Flowers consist of 5, downward-pointing petals and a 5-part central crown that are dull pink to deep pinkish-purple. Flowers are 1/4 inch wide. They form small clusters of between 10 to 20 flowers.

  • Fruits and Seeds:

    Seed pods are 2 to 4 inches long, slim, rusty-green, and have elongated tips. Pods split lengthwise when mature releasing numerous flat, oval seeds. The brown seeds are 3/8 inch long and have winged margins and long, silky tufts of white hair at the tip.

Similar Species:

Swamp milkweed is similar in appearance to other milkweed species (Asclepias spp.) except its leaves, flowers, and seed pods are more slender. Also, the sap of this wetland milkweed is less milky than that of other species in the family.

Biology:

Swamp milkweed flowers from July through August. The plant is often found growing in several inches of water.

Toxicity:

This species is poisonous to livestock and small children if ingested in sufficient quantities.

Facts and Folklore:

  • ‘Incarnata’ was likely included in the name because it means flesh-colored or flushed with pink, which describes the color of swamp milkweed flowers.

  • Pueblo Indians harvested fibers from this plant that they used to make fishing line and sewing thread.

  • Roots of swamp milkweed were used in the treatment of various ailments.

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