By: Liz Baessler
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?
Note: 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.
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The Monarch butterfly (Danaus plexippus) is sometimes known as "the storm king" because it often most active during a storm. Its latin names means "sleepy transformation" in English, which symbolizes its ability to hibernate in Mexico, and metamorphose throughout North America. It is called the "Monarch" because of the golden ridge around its chrysalis. Below you'll find a page from the "Species at Risk in Nova Scotia: Identification and Information Guide", which describes the Monarch to a T. Click a page to see a high resolution version.
For full resolution pdf versions of these images, check out www.speciesatrisk.ca/SARGuide
Michigan Native Plants
The decline of the Monarch Butterfly (Danaus plexippus) was both boom and bane to the Native Plant industry. This iconic insect brought 'Monarch Watch ' to international prominence, fostered 'Save Our Monarchs ' and 'Project Milkweed ' campaigns. As Marlin Rice, Professor of Entomology at Iowa State University noted: "It's sort of the Bambi of the insect world."
Public awareness of Pollinators in Peril also propelled what before was a Green Industry niche into the mainstream. Native Plant Nurseries exclusively selling state or regional genotypes are seeing double-digit increases in sales. For the U.S. overall, native plants represented 17% of total Green Industry sales in 2013. Economic reality and public demand now dictate a Garden Center or Nursery offer native species with Milkweeds ( Asclepias spp. ) an obvious inclusion.
Common Milkweed ( Asclepias syriaca ) and Swamp Milkweed will certainly be included in this perfunctory 'Native Plant' order. Both are probably sold with little or no consumer interaction either could be the consumers first Native Plant purchase. The result in many cases is an overall negative view of Native Plants. Regrettable for a genus with wholesale environmental benefits and species able to thrive in adverse settings.
As every farmer knows, Common Milkweed is a colonizing species, perfect for naturalization — a native meadow or pollinator ditch planting. This is a robust species adaptable to a wide range of soil, light, and moisture conditions. But planted in the perfect soil of a formal garden, its 6" deep creeping rhizome becomes a yearly reminder of a purchase gone bad.
Sweet scented Swamp Milkweed ( Asclepias incarnata ) is a moisture-loving Milkweed native to a wide variety of moist and wet environs. It is also an excellent background plant in mesic to mesic-wet full-sun settings with height dependent on available moisture. But this species should come with a product warning: like the Cutleaf Coneflower ( Rudbeckia laciniata ) , new growth is an aphid magnet. Our customers have embraced this penchant as an alternative to pesticides. With pair of scissors, kleenex or garden hose and their bi-weekly visual inspection, aphid infestations are controlled at the onset, either discarded with the yard waste, wiped or sprayed away.
Make room in your garden for Butterflyweed's ( Asclepias tuberosa ) long-lasting striking red-orange to yellow-orange bloom and quality as a cut flower. Though adaptive to all soils including loam or clay if they are well-drained, the preference is full sun, mesic to dry conditions in an acidic soil that is sandy or rocky. Butterflyweed will bloom the first year if started early, may take 2-3 years to truly become established, and does NOT transplant well due to its deep taproot. This species performs markedly better in bare, uncovered ground so lightly mulch if you must. Since crown rot can be a problem, plant away from emitters if you have a drip system.
I have created a place for Whorled Milkweed's ( Asclepias verticillata ) delicately leaved stems and later white bloom in my clay-loam woods. Though tolerating moist garden soils and part-shade, the preference is full sun, mesic to dry conditions in coarse soils. Though the lower leaves may turn yellow and fall off or the foliage of the entire plant become yellowish in times of drought, Monarch caterpillars prefer this species in my garden. I consider Whorled Milkweed mildly colonizing though not invasive. And do not grow if you have grazing animals being one of the more toxic Milkweeds.
Like Whorled Milkweed, Clasping Milkweed ( Asclepias amplexicaulis ) and Green Comet Milkweed ( Asclepias viridiflora ) thrive in full sun, but even drier sites (mesic dry to dry) again preferring poorer soils. Clasping Milkweed is a beautiful alternative to Common Milkweed for sandy, dry gardens. With alternating pairs of purple highlighted clasping leaves and a more open and deeper pink bloom, it does not disappoint. A little tricky to establish but worth the effort. Green Comet Milkweed is not for everyone having an inconspicuous bloom and declining rapidly post-bloom. It is a 'Bragging Rights' species perfect for name-dropping when in bloom on those impromptu but planned garden tours!
The Milkweed star of my woodland garden is Poke Milkweed ( Asclepias exaltata ). This attractive tall-growing milkweed has dark green glabrous leaves and drooping clusters of bicolored flowers borne on individual stems. Native to woodland openings and edges, the preference is part, dappled or bright shade, mesic conditions, in a rich sandy loam liberally supplemented with organic matter. It will take two years to establish its deep taproot, becoming a multi-stem 3-5' tall plant with a 2' spread. I find this species the perfect overplanting to mark spring ephemerals since foliage is slow to emerge. Choose sites which offer protection from prevailing winds.
I also grow two non-native Milkweeds onsite: Purple Milkweed ( Asclepias purpurascens ) , a northern Indiana genus compliments of Chad Hughson at Kalamazoo's Hidden Savanna Nursery Tropical Milkweed ( Asclepias curassavica ) when I can find it offered locally.
Purple Milkweed is less aggressive than Common Milkweed with a desirable deeper color purple bloom. It is still a colonizing species and should be planted contained in formal gardens. Purple Milkweed will adapt to heavier clay loams and tolerate light / bright shade. Monitor during drought for wilting and do not hesitate to apply supplemental water.
You may know the problem with Tropical Milkweed — the presence of OE or Ophryocystis elektroscirrha , a parasite whose only hosts are the Monarch and Queen Butterfly. This is not a problem in northern climes where the plant is grown as an annual it is recommended that gardeners in Zones 7-11 cut plants back to the ground a couple times each season allowing new and OE free foliage to emerge. Being a succulent, Tropical Milkweed is an aphid magnet requiring weekly monitoring and the occasional hosing to dislodge an infestation. But this species is 'Chocolate Cake ' to Butterflies and blooms continuously to the frost. I religiously deadhead specimens to maximize the bloom since it will seed & flower simultaneously.
Milkweeds love sand. For all I have a supply of builders sand onsite for potting seedlings and created micro-climes — +50% sand with compost and fine / sifted wood chips, elevated for drainage in my improved clay-loam. Acidify Butterflyweed's mix using pine chips, sphagnum &/or an acidic compost from Pine / Oak / Beech rather than Maple.
In formal gardens or when planting a Milkweed Garden, consider digging-in and planting colonizing Milkweeds — Common Purple Sand — within a bottomless 2800cm / 5gal nursery container an inch or two below ground level. Even if frost-heaved to the surface, once mulched the edges disappear solving the problem of escape!
Milkweed is the sole food source of Monarch caterpillars and the Milkweed Tussock Moth (Euchaetes egle ) who are immune to and use the toxins ingested with the leaf material as a defense mechanism.
For the same reason, ALL MILKWEED SPECIES ARE DEER RESISTANT.
Persons with sensitive skin should always wear gloves when handling Milkweed spp. Wash your hands thoroughly when finished, normal precautions when handling any plant material.
If you suspect Milkweed sap in your eyes either directly or indirectly from sweat or hand to eye contact, seek medical attention immediately ! Do not ATTEMPT to drive yourself!
Asclepias spp. produce some of the most complex flowers in the plant kingdom, comparable to orchids in complexity
Confirmation arrived Mid-July, 2017 that this property is an 'Urban Oasis' — residential pollinator-friendly habitats with the goal of creating Native Bee habitats and corridors for migrating butterflies. Our first Monarchs in two seasons have taken up residence, returning hourly to the Milkweeds and blooms and bog. Evidently they have nowhere else to go . . . . . a leaf cutter bee is nesting in a wallstone crack, visiting the cats water dish a couple times each hour and refusing to use the nesting box . . . . . 'Mr. BeeBalm' (Snowberry Clearwing Moth - Hemaris diffinis ) returned with the Monarda spp. and Coneflower bloom . . . . . except to this City yard.
If you're planning a Pollinator Garden, my most-shared hyperlinks:
From the Michigan State University Extension:
Attracting Beneficial Insects with Native Flowering Plants Extension Bulletin E-297 - Excellent introduction to Natural Enemies, both Predators and Parisitoids, and 'Bloom Progression', planning so that something is in bloom throughout the growing season. I DO NOT RECCOMEND planting listed species Wild Strawberry - Fragaria virginiana and Canadian Anemone - Anemone canadensis , being perhaps too aggressive for a residential planting.
Butterfly Plants by Wildtype's Bill Schneider, reviewed and revised by Brenda Dziedzic, author of Learn about Butterflies in the Garden . Not only a list of Native Plants that serve as larval hosts for butterflies and skippers but includes a separate listing of Nectaring Plants. As for Brenda's book, a Butterfly picture book for children 5 to 105.
Balloonplant (Gomphocarpus physocarpus)
Another interesting plant to try in your garden, that is also in this family of plants is Gomphocarpus physocarpus. It has many common names including balloonplant, balloon cottonbush, bishop’s balls or my favorite, fuzzy balls. I suspect that you have already gathered from all those common names that the plant produces something that looks like a ball or balloon, which in this case are the fruit, another follicle, similar to what we see in the other milkweeds. In fact, the species name physocarpus means “bladder fruit”.
Gomphocarpus is native to Africa and not hardy in our area, but it makes a great annual plant if you are looking for something that will grow 4 to 5’ tall with a 2 to 3’ spread, attract butterflies, be a food source for Monarch caterpillars and create a point of interest when you invite your gardening friends into your yard. The white flowers begin to appear in late summer and continue into the fall. The fuzzy, round, follicles usually grow to about 2” in diameter and may eventually ripen, split open and release seed if they are not damaged by frost before that time. The fruiting stems may also be cut and used as dried materials for fall bouquets.