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Swamp Milkweed
Asclepias incarnata
Also called marsh milkweed, rose milkweed, red milkweed and water nerveroot
Also comes in purple and white.
Swamp Milkweed blooms from June through August.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Swamp Milkweed
Plant it in full sun. It prefers moderate water. It is hardy in USDA zones 3–9. Expect it to reach about 3.5 ft tall and 2.5 ft wide at maturity, in roughly 2 years (a house reading).
Is Swamp Milkweed toxic to dogs or cats?
- Listed as toxic to dogs and cats by NC State Extension.
- Listed as poisonous to people by NC State Extension and Royal Horticultural Society.
Lists differ and none is complete. If a pet eats a plant and seems unwell, call a veterinarian or a pet poison helpline.
What was checked
Nine facts were checked against named botanical sources, each recorded beside the sources that carried it: mature height and spread, hardiness zones, sun, water, bloom months and color, the trait tags, and years to mature size, which rests on a recorded house rule where no publisher states one and is marked so. Soil, diseases, pests, toxicity and the plant's own names have not yet been read for this plant, and its trait tags are the ones a feature uses rather than every word a page prints. Each fact above carries its own mark. The planting, spacing and size sections are derived from these checked facts by a fixed rule, not checked separately, and the plant type is the library's own classification.
When to plant Swamp Milkweed
Plant Swamp Milkweed in early spring as soon as the soil is workable, or in early fall at least six weeks before your first frost, so roots establish in cool weather. In zone 6, the middle of its hardy zones 3 to 9, spring means March to May and fall means August or September. Once settled, it blooms from June to August.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 6, the middle of this plant's hardy range, start with zone 6 in March. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Swamp Milkweed get?
3.5 fttall5 ft 7 inan adult2.5 ftwideSee Swamp Milkweed in a garden plan: the planner shows it in 3D beside everything else you add, growing toward this size over the years.
How far apart to plant Swamp Milkweed
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Swamp Milkweed about 2.5 ft apart, center to center, so each plant has room to reach its full width.
Add Swamp Milkweed to a garden plan and the planner draws it at its full width, so you see the spacing before you buy.
Where these facts come from
Swamp Milkweed's height, spread, hardiness zones, sun, water, bloom months and color and trait tags were checked against 8 published sources on October 19, 2026. Each one is linked below with every fact it carried, which can include a fact this page still marks as not yet checked, because a source carrying a value is not the same as the value being held to the standard. Facts not in that list, and the planting, spacing and size sections, are not covered by these sources.
- Missouri Botanical Gardenheight, spread, hardiness zones, sun, water, bloom months and color and trait tags
- NC State Extensionheight, spread, hardiness zones, sun, water, bloom months and color and trait tags
- kb.jniplants.comJohnson's Nurseryheight, spread, hardiness zones, water, bloom months and color and trait tags
- mckaynursery.comMcKay Nurseryheight, spread, hardiness zones, water and bloom months and color
- Prairie Moon Nurseryheight, hardiness zones, water, bloom months and color and trait tags
- RHSRoyal Horticultural Societyheight, spread, sun, water and bloom months and color
- University of Illinois Extensionheight, hardiness zones, sun, water and bloom months and color
- bpb-us-w2.wpmucdn.comBaker, Redmond, Malcolm and Potter (2020), PeerJ, University of Kentuc...bloom months and color
How the checking works, and what each standard covers, is on the verified plants page.
Where it grows wild
Native to 45 states and 6 provinces
United States: Alabama, Arizona, Arkansas, Colorado, Connecticut, Delaware, District of Columbia, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, West Virginia, Wisconsin, Wyoming and 33 more
Canada: Manitoba, New Brunswick, Nova Scotia, Ontario, Prince Edward Island, Quebec
Recorded growing wild in 1,357 counties.
Range data from the World Checklist of Vascular Plants, Royal Botanic Gardens, Kew (CC BY 4.0, adapted) and USDA PLANTS. How the native range is credited.
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Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.