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.
Zones
3-9
pH Range
4.5-8
Sun
Full Sun
Days to Maturity
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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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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
USDA PLANTS Database
Sun
Full Sun
plant_species_v5.csv
Drainage
poorly (saturated >50% of year)
plant_species_v5.csv
Frost Tolerance
50°F
plant_species_v5.csv
Mature Height
4 ft
plant_species_v5.csv
Frost-Free Days
0+
plant_species_v5.csv
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 (USDA PLANTS Database). 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.
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, Pollinator Partnership.)
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.
Zones 3–9·Where Swamp Milkweed growsOpen map →
On USDA hardiness-zone overlap, Swamp Milkweed can grow in these states:
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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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 (USDA PLANTS Database). 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 (Xerces Society, Pollinator Partnership).
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.