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Swamp Milkweed
The monarch milkweed for wet soil: fragrant pink flower clusters that swarm with butterflies, a caterpillar host that thrives where the ground stays damp, and a tidy, well-behaved clump for rain gardens and pond edges.
Safety notes Like all milkweeds, swamp milkweed contains cardiac glycosides in its sap and is toxic if eaten - it is not a food plant, and it's toxic to livestock and pets in quantity. Its sap can irritate skin and especially the eyes, so wash your hands and avoid rubbing your eyes after handling or cutting it. Grow it for the monarchs and pollinators, never for the table. Unlike common milkweed it forms a tidy clump rather than running, so it's easy and safe to site in a border.
Overview
Swamp milkweed (Asclepias incarnata) is the milkweed for the wet spot - and one of the best pollinator plants a damp garden can grow. Where its famous cousins butterfly weed and common milkweed demand dry, sunny ground, swamp milkweed thrives in constantly moist to wet soil, at pond edges, in rain gardens, and in low damp corners, giving you a full monarch and butterfly plant for exactly the conditions those others hate.
The one thing to knowSwamp milkweed (Asclepias incarnata) is the milkweed for the wet spot - and one of the best pollinator plants a damp garden can grow.
Quick facts
- Sprouts in
- 18 daysRange: 10–28 days
- Soil temperature
- 70 °FRange: 65–75 °F
- Start indoors
- 8 weeks before transplantRange: 6–10 weeks
- Height
- 4 ftRange: 3–5 ft
- Spread
- 24 inRange: 18–36 in
- Cold
- Takes hard frostdamaged below -40°F
- Heat
- Struggles above 95°F
- Life cycle
- Perennial, lives about 10 years
- Save seeds
- About 130 days after plantingRange: 110–160 days
- Self-sows
- Yes, expect volunteers
- Soil
- Tolerates wet soil
- Water
- High
- Plant spacing
- 24 inRange: 18–36 in
When to plant
Fall sowing is open for 26 more days. Next: winter, Feb 13 to Feb 27.
- Direct sow Oct 11 – Nov 15 Open now · 26 days leftAbout 2 weeks before to 3 weeks after your first frost (Oct 25 here)Fall-sow seed outdoors onto moist soil so winter cold breaks its dormancy naturally - the easiest way to start it. It germinates the following spring; seed-grown plants usually bloom the second year.
- Start indoors Feb 13 – Feb 27 Opens in 116 daysAbout 8 weeks before to 6 weeks before your last frost (Apr 10 here)Cold-stratify seed in the fridge 3-6 weeks, then sow indoors 6-8 weeks before last frost for spring transplants.
- Transplant Apr 10 – May 22 Opens in 172 daysAbout at to 6 weeks after your last frost (Apr 10 here)Set out young transplants or divisions after last frost into consistently moist to wet soil in full to part sun; keep them watered and they establish quickly, often blooming the first year.
Frost here: last around Apr 10 (Mar 27 to Apr 24 most years), first around Oct 25. Zone averages, your own yard may run a week or two either way.
Life stages
Establish, grow, repeat
Getting established and returning each season are different parts of the story.
Stage 1 of 4 · Getting established
Year 1 - rooting in
Day 0 to 60 after transplanting
Care at this stage
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Keep it consistently moist to wet
Unlike its dry-soil cousins, swamp milkweed wants steady moisture. Water a new plant regularly and never let it dry out - it thrives in constantly damp to wet soil, at pond edges and in rain gardens, and tolerates ordinary garden soil only if kept watered.
-
Mulch to hold moisture
A layer of mulch keeps the roots cool and damp, which this moisture-loving milkweed appreciates. Unlike butterfly weed, it doesn't need sharp drainage - wet ground is exactly right.
Months are typical seasonal windows; climate, variety, and plant age can shift them.
Watch out for
3 to know. None are high-risk for Swamp Milkweed. None are active in October.
Drought StressSeverity Medium DisorderSeason: Jun–AugWilting on hot afternoons, browning and crisping along leaf edges and tips, premature leaf drop, collapsed flower stems, and thin, stunted growth - showing up first on young plants and on the driest, most exposed side of the planting.
The name is the instruction: swamp milkweed wants consistently moist to wet ground. It is often planted in an ordinary dry border alongside butterfly weed, which is exactly where it browns at the leaf margins and declines.
Wilting on hot afternoons, browning and crisping along leaf edges and tips, premature leaf drop, collapsed flower stems, and thin, stunted growth - showing up first on young plants and on the driest, most exposed side of the planting.
Water deeply and consistently, then mulch. Mild wilting reverses within a day or two, but a prolonged drought sets a plant back hard and can kill a young one outright. If a plant scorches every summer, the site is wrong - move it to damper ground rather than trying to water it through.
Match the site to the plant: put a moisture-loving species where the ground actually stays damp - a rain garden, pond edge, ditch, seep or low spot - rather than in an ordinary border you intend to keep watered. Mulch to hold moisture and keep the roots cool, water deeply through every dry spell while the plant is establishing, and avoid hot, windy, exposed positions.
Not a pest but a siting problem, and on a moisture-loving plant it is usually the thing that actually kills it. When the soil dries out, leaf edges brown and crisp, foliage wilts and drops early, flowering and fall color are cut short, and growth thins. Hot sun, wind and exposed positions make it worse by pulling water out faster than the roots can replace it. A plant that wants reliably moist or wet ground has no drought tolerance to fall back on, and young or recently planted ones have the least of all.
Oleander AphidSeverity Low PestSeason: Jun–SepDense colonies of vivid yellow aphids packed along the stems and over the flower buds, sticky honeydew, sooty mold, and ants working the plant.
Common on swamp milkweed's soft growth. Check for monarch eggs before wiping down a stem, and otherwise leave the colony to the lady beetles.
Dense colonies of vivid yellow aphids packed along the stems and over the flower buds, sticky honeydew, sooty mold, and ants working the plant.
Blast them off with a jet of water, or wipe them off by hand - checking first for monarch eggs and small caterpillars on the same stems. Otherwise simply tolerate them, since predators usually catch up. Do NOT spray, including with insecticidal soap or neem, which kill caterpillars too.
Encourage lady beetles and lacewings and let them do the work; a strong plant carries a heavy colony without real harm. Never use insecticide on a monarch host plant. Soft, over-watered, over-fed growth carries far more of them, so growing the plant hard reduces the problem.
Bright yellow, black-legged aphids that cluster densely on milkweed stems, buds and new growth. They are conspicuous and very common but rarely fatal to an established plant - and they cannot be sprayed, because any insecticide that kills them also kills the monarch eggs and caterpillars the plant is there to support.
Milkweed Tussock MothSeverity Low PestSeason: Jul–SepClusters of hairy orange, black, and white caterpillars skeletonizing leaves, usually on older plants in late summer.
Clusters of hairy orange, black, and white caterpillars skeletonizing leaves, usually on older plants in late summer.
None warranted; if a young plant is being overwhelmed you can move a cluster to another milkweed, but generally leave them be.
None needed - they're native and share the plant with monarchs.
A native moth whose fuzzy orange-black-and-white caterpillars feed in groups on milkweed leaves, sometimes stripping older foliage late in the season - a natural part of the milkweed community, not a problem to control.
Good & bad neighbors
Plant nearby
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A classic wet-soil native pairing: cardinal flower's scarlet hummingbird spikes beside swamp milkweed's pink monarch flowers, both thriving in rain gardens and pond edges and serving different pollinators.
-
Two tall, late-summer, moisture-loving butterfly plants - Joe-Pye weed's mauve domes and swamp milkweed's pink clusters make a rain-garden pollinator powerhouse and a monarch waystation together.
-
A native wetland iris for the same wet ground, blooming earlier and adding sword foliage and structure beneath and around the milkweed clumps at a pond edge.
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A wet-site native shrub whose white pincushion flowers rise behind swamp milkweed's pink clusters, both butterfly magnets that thrive in the same saturated ground.
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Planting several milkweed species gives monarch caterpillars more host leaves across different conditions - swamp milkweed covers the wet ground common milkweed can't tolerate.
- Traditional pairings, thin evidence
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The dry-soil monarch milkweed to swamp milkweed's wet-soil one; together across a garden's moist and dry areas they extend monarch host coverage through varied conditions.
Varieties · 4
You pick one when you add Swamp Milkweed to your garden. Its days to maturity set your harvest window.
Swamp Milkweed (Asclepias incarnata)
The wild species: upright 3-5 foot clumps topped with domed clusters of fragrant soft-pink flowers, a monarch host and top butterfly-nectar plant for moist to wet soil.
Variety details for Swamp Milkweed (Asclepias incarnata)
Upright clumps of narrow leaves topped with domed clusters of soft pink vanilla-scented flowers.
speciesnativepinkmonarch-hostTidy and non-running - the border- and rain-garden-friendly milkweed for damp ground.
Cinderella
A selection with larger, deeper rose-pink flower clusters and a strong sweet fragrance on sturdy clumps - the same monarch and butterfly value as the species with a showier, more uniform bloom.
Variety details for Cinderella
Full domed clusters of deep rose-pink, sweetly scented flowers on strong stems.
rose-pinkfragrantcut-flowerselectionExcellent in a rain garden or moist border.
Ice Ballet
A crisp white-flowered selection with the same wet-soil toughness and monarch value, its clean white clusters cooling and brightening a damp planting and pairing beautifully with the pink forms.
Variety details for Ice Ballet
Domed clusters of pure white flowers on upright leafy clumps.
whitefragrantcut-flowerselectionA fine cut flower.
Soulmate
A vigorous rose-pink selection with large fragrant flower heads and a strong upright habit, quick to establish and bloom - a dependable, showy monarch milkweed for moist borders and rain gardens.
Variety details for Soulmate
Large domed clusters of rich rose-pink flowers on tall sturdy clumps.
rose-pinkvigorouscut-flowerselection
Grower tips
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