Swamp Milkweed is a perennial grown for its red blooms, which open in fall and return year after year. It's hardy across USDA zones 3 through 9, shrugs off deer and grows just as well in a container as in the ground. Its fall flowers are a real draw for honeybees, native bees, butterflies, and moths.
Swamp Milkweed — the short answer
Swamp Milkweed: grown in zones 3–9, full sun, pH 4.5–8.
- USDA zones
- 3–9
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- Soil pH
- 4.5–8
- FAO ECOCROP
- Sun
- Full Sun
- Growable Ground Plant Database
- Frost-kill temperature
- 32°F
- FAO ECOCROP
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — each tile names its own row's source, because per-field provenance varies.
Score Swamp Milkweed on your exact land.
Zone averages can't see the slope, soil, frost, and sun that decide whether swamp milkweed actually takes — and those shift from one yard to the next. Enter your address and we'll score swamp milkweed against your land's real conditions.
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The full pollinator story for swamp milkweed:
Monarch Host Plants: Which Milkweed Is Native to Your StateSee Swamp Milkweed
What Swamp Milkweed is
Swamp Milkweed grows as a perennial and reaches around four feet at maturity. It blooms red in fall. It's also deer-resistant and well suited to containers.
How to grow Swamp Milkweed
Swamp Milkweed grows in USDA zones 3 through 9. Swamp Milkweed does best in full sun — at least 6 hours of direct sun a day — and soil from pH 4.5 to 8, on consistently moist ground.
USDA Zones
3-9
USDA PHZM 2023
Soil pH
4.5 - 8
FAO ECOCROP
Sun
Full Sun
Growable Ground plant catalog
Drainage
poorly (saturated >50% of year)
Growable Ground plant catalog
Frost Kill Temperature
32°F
Where cold starts killing growing tissue. Not a winter-survival floor — a dormant perennial takes far colder, which its hardiness zone answers.
FAO ECOCROP
Minimum Growing Temperature
50°F
Below this it stops growing rather than dies — a pace limit, not a survival limit.
FAO ECOCROP
Mature Height
4 ft
Growable Ground plant catalog
Frost-Free Days
0+
The frost-free stretch it needs start to finish — short-season areas may need an indoor head start.
Growable Ground plant catalog
Start the season right
Plant swamp milkweed in full sun with at least 6 hours of direct sun, once the soil has warmed and frost risk has passed.
Match the soil
Swamp Milkweed prefers pH 4.5 to 8 (FAO ECOCROP). A quick soil test from your local Extension lab tells you whether to add lime or sulfur to land in band.
Water steadily
Keep the root zone evenly moist through establishment. Match watering to the plant's drainage preference and your local rainfall.
Harvest at its peak
Cut swamp milkweed blooms in the cool of the morning, just as they open, for the longest display.
Where Swamp Milkweed thrives
Swamp Milkweed is hardy across USDA zones 3 through 9. Zone is only the starting point, though: the soil pH, drainage, and frost dates on your specific land decide how well it actually does.
A USDA zone is a 10°F band of average annual extreme winter minimum, so zones 3–9 spans average winter lows from -40°F to 30°F (USDA PHZM 2023). Across the 50 states and DC, that band covers 42 outright and splits 9 more down the middle — and which side of that line your land sits on changes the answer.
Zones 3–9·Where Swamp Milkweed growsOpen map →
Where Swamp Milkweed stands, state by state
Swamp Milkweed is rated for zones 3–9 — a cold floor USDA puts at -40 to -30°F. Across the 50 states and DC, 42 sit fully inside that band, the line runs through 9 more, and 0 sit outside it — and inside every split state, the same line runs on at county grain.
Fully inside zones 3–9
42 states
3 of 42 shown
The line runs through
9 states
- Alaska · zones 1a-9a
- California · zones 4b-11a
- Nevada · zones 4a-10a
3 of 9 shown
Swamp Milkweed’s band covers part of each of these states — which side of the line your county sits on changes the answer, and each state page draws it.
State zone extents: USDA Plant Hardiness Zone Map (PHZM) 2023. A zone is a 10°F band of average annual extreme minimum temperature, so a state that splits the band contains the boundary — its own page draws the county line, and a parcel report resolves which side your land sits on.
What grows around Swamp Milkweed
Growing guides for swamp milkweed
In rotation planning, swamp milkweed counts as a Other — beds recover best when other crops don’t follow each other in the same spot year over year. (Growable Ground derivation — crop-rotation group from botanical family)
Related plants in perennial flower
Good to know
One caution for pet owners — swamp milkweed is toxic to dogs and cats (moderate severity). Keep it out of reach, and call ASPCA Animal Poison Control at (888) 426-4435 in an emergency. (Source: ASPCA.)
Swamp Milkweed is a standout pollinator plant — high value to bees and other pollinators. (Source: Xerces Society.)
Your land is one point inside Swamp Milkweed's range
This page resolves to the species. Your state page draws the county line, and a report reads the parcel — the soil pH, drainage, sun, and frost dates on your exact ground, which no species average can see.
See if Swamp Milkweed will thrive on your land
Zone averages are a start. Your exact soil pH, drainage, sun exposure, and frost dates shape whether swamp milkweed actually takes — we score it against the real conditions at your address.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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How we know this about Swamp Milkweed
The figures above are cited per row, not per site: the pH band names this plant’s own source column, the three temperature figures each carry their own, and days-to-maturity cites the publication that actually lists it. All of it comes from the Growable Ground Plant Database — a compilation over FAO ECOCROP, USDA PLANTS, and university Extension sources, published openly with per-field provenance.
Grounded inUSDA PLANTS Database•USDA PHZM•ASPCA
Frequently asked questions
Can I grow Swamp Milkweed in my zone?
Swamp Milkweed grows in USDA hardiness zones 3 through 9 (USDA PHZM 2023). Zone is one factor — soil pH, drainage, and frost dates on your specific parcel also shape whether it takes.
When should you plant Swamp Milkweed?
Most growers plant swamp milkweed after the last spring frost, once the soil has warmed. Your local frost dates set the exact window — a Growable Ground report reads them for your address.
How much sun does Swamp Milkweed need?
Swamp Milkweed needs full sun — a spot that catches at least 6 hours of direct summer sun a day. In more shade it still grows, but usually gives a smaller, later crop. The catch is that a yard rarely gets even light everywhere — a fence, the house, or one tall tree can quietly take those hours. A Growable Ground report reads the real sun-hours across your land, canopy and buildings included, so you can pick the brightest bed before you plant.
What soil does Swamp Milkweed need?
Swamp Milkweed prefers soil pH 4.5 to 8, on consistently moist ground (FAO ECOCROP). Your report scores your parcel's actual soil against that using USDA SSURGO data.
Does Swamp Milkweed attract pollinators?
Yes — swamp milkweed's flowers are a strong nectar and pollen source for honeybees, native bees, butterflies, and moths. (Source: Xerces Society.)
Is Swamp Milkweed safe for pets?
Swamp Milkweed is toxic to pets (dogs,cats) with moderate severity. Keep it out of reach, and call ASPCA Animal Poison Control at (888) 426-4435 in an emergency. (Source: ASPCA.)