Whorled milkweed

Sun

Full sun; tolerates light partial shade but flowers less freely.

Water

Low once established; water new plants during dry spells and avoid persistently wet soil.

Soil

Well-drained sandy, gravelly, rocky or loamy soil; tolerates poor soil and clay where drainage is good.

Height

1-3 ft (0.3-0.9 m)

Spread

1-2 ft (0.3-0.6 m) initially; colonies can spread farther through underground stems.

Flowers

Summer into early autumn; small, creamy-white to greenish-white flowers in rounded clusters.

Foliage

Very narrow green leaves arranged in whorls around upright stems; foliage dies back for winter.

Growth

Moderate; young plants may establish slowly before spreading.

Care needed

Low

• Pollinators
• Deer resistant
• Drought tolerant
• Cold hardy
• Heat tolerant
• Wildlife
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Easy

Toughness

Very tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   1.2 ft (0.38 m)

3. After 2 years

   1.5 ft (0.45 m)

4. After 3 years

   1.7 ft (0.53 m)

5. After 5 years

   2 ft (0.6 m)

   full size

About 4 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Toxic

Native to

the US and Canada

In the garden

Spreads vigorously: plan to contain it.

Growth rate

Slow

• Water through the first growing season when the root zone becomes dry; established plants usually need little supplementary water.
• Avoid routine feeding; rich soil and excess nitrogen can encourage weak, floppy growth.
• Use only a light mulch and keep it away from emerging shoots, especially in damp climates.
• Remove unwanted shoots at the edge of the colony, digging out their connecting underground stems.
• Mark the planting spot because shoots can emerge late in spring.

Pruning. Leave stems and seedpods standing through winter where practical, then cut dead stems close to the ground in late winter or early spring. If seedlings are unwanted, remove pods before they split, checking first for caterpillars.

Late winter

Cut down last year's dead stems before new shoots appear.

Spring

Plant nursery-grown plants after the soil becomes workable; mark their positions and water them in.

Late spring

Check for emerging shoots before weeding, and remove growth spreading beyond the intended patch.

Summer

Water new plants during drought and inspect leaves for monarch eggs or caterpillars before treating pests.

Late summer

Remove developing seedpods if you do not want windblown seedlings.

Autumn

Sow fresh seed outdoors in a protected seedbed or pots so winter cold can help break dormancy.

• Plant in loose groups among little bluestem and prairie dropseed for fine-textured meadow planting.
• Use in sunny gravel gardens where its pale flowers soften stones and coarser foliage.
• Combine with purple coneflower and black-eyed Susan for a long-season pollinator border.
• Allow colonies to develop in a North American native planting, away from tightly controlled bed edges.

Garden styles it suits: Native meadow, Midwest prairie, Pollinator garden, Wildlife garden, Dry gravel garden and New perennial (prairie).

Plant it with: Little bluestem, Prairie dropseed, Purple coneflower, Black-eyed Susan, Wild bergamot and Aromatic aster.

Wildlife: A larval host for monarch butterflies within their range. The flowers provide nectar for bees, butterflies and other insects; milkweed bugs and several specialist beetles may also feed on the plant. Caterpillar feeding is normally a reason to keep the plant, not spray it.

• Oleander aphids cluster on tender shoots: tolerate small colonies or wipe them off by hand, checking carefully for monarch eggs and young caterpillars.
• Root or crown rot in wet soil: improve drainage or move plants to a drier site rather than watering on a fixed schedule.
• Floppy stems and sparse flowering in shade or rich soil: provide more sun and stop nitrogen feeding.
• Unwanted colonies or seedlings: dig out spreading underground stems and remove pods before they open.

Toxic to people, cats, dogs and horses if eaten; all parts should be treated as poisonous, including dried material. Whorled milkweed can cause serious, potentially fatal livestock poisoning, so keep it out of pasture and hay. Its milky sap can irritate skin and injure eyes; wear gloves when cutting it and seek urgent medical or veterinary advice after suspected ingestion.

Where it spreads. Can spread assertively by underground stems and windborne seed in suitable garden soil, including within its native central and eastern North American range. Keep it out of small, tightly planted beds if you cannot manage its spread.

• Butterfly weed (Asclepias tuberosa)

  Usually has orange flowers and broader, mostly alternate leaves rather than threadlike leaves in whorls; it also lacks the conspicuous milky sap typical of whorled milkweed.

• Flowering spurge (Euphorbia corollata)

  Has much broader leaves and airy, branching sprays of tiny white flower-like structures rather than rounded clusters of distinctive milkweed flowers. Both plants contain irritating milky sap.

Asclepias refers to Asclepius, the Greek god of medicine, while verticillata means whorled, describing the leaves arranged around each stem.

Propagation. Sow fresh seed outdoors in autumn, or give stored seed about 30 days of cold, moist stratification before spring sowing. Divide established colonies in early spring, retaining roots and buds on each section; avoid repeatedly disturbing young plants.

Accepted botanical name

Asclepias verticillata

In the US and Canada

Native in Canada and the lower 48 states.

Native range

Alabama, Arizona, Arkansas, Connecticut, Delaware, District of Columbia, Florida, Georgia, Illinois, Indiana, Iowa and Kansas.

Measured

Average height 47 cm.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.