Swamp milkweed
Asclepias incarnata
also called rose milkweed, pink milkweed
The garden-mannered milkweed: clumping instead of running, with vanilla-scented dusty-pink umbels in high summer and every bit of the monarch value of its rowdier cousins.
- Type
- Flower · Perennial
- Botanical family
- Mixed / other
- Foliage color
- Green
- Flower color
- Pink
- Sunlight
- Full sun
- Watering
- Moderate to high
- Soil
- Moist to wet, but content in ordinary garden soil
- Feeding
- Gentle all-organic
- USDA zones
- 3a–9a
- Frost tolerant
- Yes
- Sow indoors
- 56 days before the last spring frost
- Sow direct
- 21 days before the last spring frost
- Plant out
- at the last spring frost
- Plant spacing
- 23.6 in
- In-row spacing
- 17.7 in
- Between rows
- 2 ft 6 in
- Square-foot density
- Not suited to SFG
- Sow depth
- 0 in
- Root system
- Clumping rhizomes
- Working depth
- 6–16 in
- Can reach
- 24 in down where the soil allows
- Spread
- 24 in–3 ft across, about 1–1.5× the width of the plant
- Shallowest pot
- 10 in of soil
The clump widens a little each year from a shallow rhizome that likes to sit at or just under the surface. When the middle goes bare and woody, lift the whole thing, keep the young outer pieces and throw the centre away.
The habit is Swamp milkweed’s own; the figures are what that habit usually comes to at this size, not a measurement of this species. Roots follow the soil either way: a compacted pan, a high water table or heavy clay stops them well short of any of it, and deep open ground lets them go further.
- Cats and dogs
- Recorded toxic
Recorded as toxic to cats and dogs by ASPCA.
The ASPCA row names the genus only, which covers our Asclepias incarnata.
- When
- Not harvested. Collect seed in fall if you want more plants, which you will.
- What to look for
- Pods going from green to buff and just starting to split, the silk still flat inside.
- How to harvest
- Pick pods at the split, strip the silk off the seed indoors (a coin in a jar, shaken, does it), and sow outside in fall — the seed needs winter cold to wake.
- How often
- One seed gathering; deadhead the first flush of flowers in summer for a second.
- Storing the crop
- Cleaned seed keeps a winter in a paper envelope in the fridge, but fall sowing where it is to grow works best. Cut stems down in spring, not fall — native bees winter in them.
Beneficial predators that hunt this plant's pests — grow their favourite flowers nearby to recruit them. companion plant
- Aphid midge Aphidoletes aphidimyzaHunts Aphids
A tiny midge whose orange maggots paralyze aphids and drink them dry, twenty or more each. Sold as a greenhouse biological control and resident outdoors wherever there are small nectar flowers and an unsprayed aphid colony to find.
- Assassin bug ReduviidaeHunts Aphids
A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be.
- Big-eyed bug Geocoris spp.Hunts Aphids
A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide.
- Damsel bug NabidaeHunts Aphids
A slender, mantis-armed bug that grabs aphids, small caterpillars, and thrips in low crops and meadowy edges. Leave a strip of unmown grasses and flowers for it to overwinter in.
- Dragonflies & damselflies OdonataHunts Aphids
Aerial hunters that take mosquitoes, midges and small flies on the wing all day, and whose larvae spend a year or more clearing the same insects from the water. A pond with planted margins and no fish is the way to have them.
- Garden birds PasseriformesHunts Aphids
Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray.
- Green lacewing Chrysoperla carneaHunts Aphids
Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing.
- Hoverfly SyrphidaeHunts Aphids
Bee-mimicking flies whose legless larvae graze aphid colonies clean while the adults pollinate. A ribbon of shallow, nectar-rich flowers kept in bloom all season recruits wave after wave of them.
- Ladybird (lady beetle) CoccinellidaeHunts Aphids
The gardener’s favorite ally: adults and their alligator-shaped larvae each eat thousands of aphids, plus scale, mealybugs, and other soft-bodied sap-suckers. Grow flat, open flowers for the adults and never spray a colony that ladybird larvae are already working.
- Minute pirate bug Orius spp.Hunts Aphids
A pinhead-sized true bug that is the best natural check on thrips, and happily spears aphids, mites, and insect eggs too. It needs pollen when prey is scarce, so keep something flowering nearby.
- Parasitic wasps Braconidae & TrichogrammaHunts Aphids
Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled.
- Praying mantis MantidaeHunts Aphids
A sit-and-wait ambusher that snatches caterpillars, beetles, and anything else that wanders close — friend and foe alike, so count it a mixed blessing. Tall, structured plantings give it perches and egg-case anchors.
- Soldier beetle CantharidaeHunts Aphids
Soft-winged beetles seen mating on flower heads in high summer; adults and larvae both take aphids and soft grubs. Open composite flowers are their landing pads and hunting grounds.
- Spiders AraneaeHunts Aphids
Webs, ambushes, and night patrols make spiders the garden’s steadiest generalist predators, taking whatever flies or crawls past. Mulch, ground cover, and undisturbed corners keep the population dense.
Monarchs lay on it as readily as on common milkweed, and in a border it behaves: deep taproot, no runners, a tidy clump. It emerges very late in spring, so mark the spot before you plant a "gap" on top of it.
The Cottage Garden Companion — the gardener's herbarium at cottagegardencompanion.com