Heirloom

Swamp Milkweed

Asclepias incarnata

Wikimedia Commons

Blooms summer through frost. Clusters of rose to mauve florets on sturdy stems. In our trials the species is nearly identical to the variety Soulmate. Attractive lance-shaped leaves. Use for cut flowers and garden beds. Attracts butterflies and hummingbirds. Larval host for monarch butterflies. Native to North America. Also known as pink milkweed and rose milkweed. Perennial in Zones 3-8.

Harvest

120-130d

Days to harvest

📅

Sun

Full sun to partial shade

☀️

Zones

3–9

USDA hardiness

🗺️

Height

3-5 feet

📏

Planting Timeline

Zone:

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Transplant

Direct Sow

Transplant

Direct Sow

Showing dates for Swamp Milkweed in USDA Zone 7

All Zone 7 native-wildflower →

Zone Map

Click a state to update dates

Swamp Milkweed · Zones 3–9

What grows well in Zone 7? →

Growing Details

Difficulty

Easy

Spacing18-24 inches

SoilMoist to average well-drained soil, slightly acidic to neutral pH

WaterHigh — consistent moisture needed

SeasonPerennial

ColorRose to mauve

Zone-by-Zone Planting Calendar

Zone	Indoor Start	Transplant	Direct Sow	Harvest
Zone 3	—	June – August	May – July	—
Zone 4	—	June – July	April – June	—
Zone 5	—	May – July	April – June	—
Zone 6	—	May – July	April – June	—
Zone 7	—	May – June	March – May	—
Zone 8	—	April – June	March – May	—
Zone 9	—	March – May	February – April	—
Zone 10	—	March – April	January – March	—

Complete Growing Guide

Light: Full sun (6 or more hours of direct sunlight a day), Partial Shade (Direct sunlight only part of the day, 2-6 hours). Soil: Clay, High Organic Matter, Loam (Silt). Soil pH: Acid (<6.0), Neutral (6.0-8.0). Drainage: Good Drainage, Moist, Occasionally Wet. Height: 3 ft. 0 in. - 5 ft. 0 in.. Spread: 2 ft. 0 in. - 3 ft. 0 in.. Spacing: 3 feet-6 feet. Growth rate: Medium. Maintenance: Low. Regions: Coastal, Mountains, Piedmont.

Harvesting

3-4-inch long follicle seed pods split on one side to release seeds with tufts of hair that float on the wind. They are green and mature to brown.

Color: Brown/Copper, Cream/Tan, White. Type: Follicle. Length: > 3 inches. Width: 1-3 inches.

Garden value: Showy

Harvest time: Fall

Storage & Preservation

Swamp milkweed is maintained fresh as a cut flower rather than stored as food. Arrange fresh stems in a vase with room-temperature water, changing water every 2-3 days and recut stems by 1 inch every 3-4 days. Stems last 7-10 days in a cool room away from direct sun and ripening fruit.

For seed preservation, allow mature seed pods to dry completely on the plant until they split open naturally. Collect seeds in a paper bag and store in a cool, dry location (50-60°F, low humidity) in an airtight container for up to 3 years. For maximum germination rates in future seasons, store seeds in the refrigerator after the first month.

Pressed flowers from swamp milkweed dry beautifully for botanical crafts. Layer fresh flower clusters between absorbent paper and press under heavy books for 2-3 weeks in a warm, dry place.

History & Origin

Origin: Central & E. Canada to W. Central & E. U.S.A.

Advantages

+Attracts: Butterflies, Pollinators, Predatory Insects
+Low maintenance

Considerations

-Toxic (Flowers, Fruits, Leaves, Roots, Seeds, Stems): Low severity
-Causes contact dermatitis

Companion Plants

Joe Pye Weed, Wild Bergamot, and New England Aster are the strongest pairings here. All three share similar moisture preferences — they won't compete for water the way drought-tolerant prairie species would — and their bloom times span from midsummer through October, which keeps pollinators cycling through the planting long after Asclepias incarnata's own flowers have finished. That matters because monarch adults need nectar sources beyond milkweed itself; a monoculture of milkweed feeds caterpillars but not the adults passing through in August and September. Cardinal Flower and Blue Flag Iris round out a wet-to-moist guild well: same soil tolerance, no allelopathic interference, and they occupy different vertical space without crowding Asclepias incarnata's 18-24 inch spread.

The harmful companions are problems for different reasons. Black Walnut produces juglone, a root-zone compound that suppresses many native perennials — keep swamp milkweed well outside the canopy drip line, which on a mature walnut can extend 60 feet or more. Purple Loosestrife and Crown Vetch are both invasive; either one will outpace and displace the native species you're actually trying to establish, so don't plant them anywhere near a native wildflower bed regardless of what else is growing there.

Plant Together

Joe Pye Weed

Similar moisture and sun requirements, attracts complementary pollinators and creates beneficial habitat

Cardinal Flower

Thrives in same wet conditions, attracts hummingbirds and creates layered pollinator garden

Blue Flag Iris

Compatible wetland plant that provides structural diversity and different bloom timing

Wild Bergamot

Attracts beneficial insects and pollinators while tolerating similar moisture conditions

New England Aster

Extends blooming season into fall, supports monarch butterflies during migration

Boneset

Native wetland companion that attracts beneficial insects and provides late-season nectar

Turtlehead

Shares preference for moist soil and partial shade, attracts specialized native bees

Wild Ginger

Provides ground cover in moist conditions without competing for pollinators

Keep Apart

Black Walnut

Produces juglone which is toxic to many plants including milkweeds

Eucalyptus

Allelopathic oils inhibit growth of nearby native plants

Crown Vetch

Aggressive invasive ground cover that can smother native wildflowers

Purple Loosestrife

Invasive wetland plant that outcompetes native species for resources and space

Pests & Disease Resistance

Common Pests

Milkweed beetles, aphids

Diseases

Root rot if overwatered; fungal leaf spots in humid conditions

Troubleshooting Swamp Milkweed

What you'll see, why it happens, and what to do about it.

Stems and undersides of leaves coated in clusters of small orange or yellow insects, usually appearing in early summer

Likely Causes

Milkweed aphid (Aphis nerii) — they colonize fast and are almost always present on milkweed at some point
Absence of predatory insects early in the season before ladybug and lacewing populations build

What to Do

1.Knock them off with a firm spray of water — this works better than it sounds and doesn't harm monarch caterpillars the way insecticidal soap can
2.Leave light infestations alone; ladybugs will show up within a week or two and do the work for you
3.If the plant is heavily distorted and caterpillars aren't present, cut the affected stems back by half and dispose of the cuttings in the trash

Red and black beetles with long antennae chewing holes in leaves and seed pods, late summer into fall

Likely Causes

Milkweed beetle (Tetraopes tetrophthalmus) — a native species that feeds almost exclusively on milkweed and is part of the plant's ecology
Red milkweed beetle larvae also bore into roots, though this rarely kills an established plant

What to Do

1.Hand-pick adults into soapy water if the feeding damage is severe enough to bother you
2.Accept a moderate population — this beetle is native, not going to wipe out a healthy clump, and birds eat them
3.If root boring is suspected on a young plant (wilting despite adequate moisture), dig and inspect; replace the plant and rotate the spot next season

Crown or roots turning brown and mushy, plant collapsing even when the surrounding soil is wet

Likely Causes

Root rot — most often Phytophthora or Pythium species — triggered by waterlogged soil or heavy clay that doesn't drain between rain events
Planting in a low spot that pools after rain; Asclepias incarnata handles wet feet better than most milkweeds, but stagnant standing water is a different problem

What to Do

1.Dig the plant, cut away all rotted material with a clean knife, and move it to a spot with at least modest drainage — even a 6-inch grade change helps
2.Before replanting in clay, work in coarse sand and compost so the bed drains within 2-4 hours after a soaking rain
3.Don't confuse normal late-season dieback (this plant goes fully dormant and looks completely dead) with rot — check the crown in early spring before giving up on it

Frequently Asked Questions

How long does swamp milkweed take to flower from seed?▼

Swamp milkweed typically matures in 120-130 days from germination to first flowers. Seeds started indoors 6-8 weeks before your last frost will usually flower by mid to late summer the same year. Plants grown from seed are often less vigorous in year one; expect the most abundant flowering in year two when the root system is fully established.

Is swamp milkweed good for beginners?▼

Yes—it's rated 'easy' and adapts to varied conditions once established. The main beginner mistakes are overwatering in year one and expecting full flowering in the first season. Start from seed indoors to control seedling vigor, provide consistent moisture through establishment, and defer major harvesting until year two. Beyond that, it requires minimal care.

Can you grow swamp milkweed in containers?▼

Yes, in containers 12+ inches deep and wide with drainage holes. Use quality potting mix (not garden soil) and keep consistently moist through the growing season—containers dry faster than in-ground plantings. Pot-grown plants are ideal for controlling spread in small gardens, but expect them to flower more modestly than in-ground plants and require division or fresh soil every 2-3 years.

Why is swamp milkweed important for monarch butterflies?▼

Swamp milkweed is a larval host plant—the *only* plant monarch caterpillars will eat. Without milkweed, monarchs cannot complete their life cycle. Cultivating swamp milkweed directly supports monarch populations and contributes to critical conservation efforts. A single mature plant can sustain 50+ caterpillars through development to chrysalis.

What's the difference between swamp milkweed and common milkweed?▼

Swamp milkweed (Asclepias incarnata) produces rose-pink flower clusters on multiple thin stems reaching 3-5 feet, blooms mid-summer through frost, and tolerates average to moist soil. Common milkweed (Asclepias syriaca) has pink-purple flowers on single thick stems reaching 4-6 feet, blooms only 4-6 weeks in early summer, and spreads aggressively via rhizomes. Swamp milkweed is better for smaller gardens and extended monarch support.

Do I need to deadhead swamp milkweed?▼

Deadheading spent flower clusters promotes continued blooming and neater appearance. However, if you want seeds for self-sowing or future propagation, allow some flower clusters to mature into seed pods (follicles) until they split naturally in late summer. Both approaches are viable—choose based on your garden design and propagation goals.