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Asclepias, Genus,

Genus

milkweeds

Apocynaceae

The Americas (greatest diversity in North America), with a few species in Africa

Attracts Pollinators Attracts Butterflies Attracts Hummingbirds Deer Resistant Drought Tolerant Fragrant (moderate)

SunFull Sun

WaterMedium · drought-tolerant

HardinessZones 3–9

Overview

Asclepias is a genus of about 140 species of perennial herbs in the dogbane family (Apocynaceae), known as milkweeds. Most species form erect, unbranched or sparingly branched stems 1-5 feet (30-150 cm) tall, and the majority exude a milky white latex when cut, though A. tuberosa has clear sap. Leaves are opposite or whorled, lance-shaped to oval, 2-6 inches (5-15 cm) long. The flowers are borne in rounded umbels and have an intricate structure: five reflexed petals below a central crown of five upright hoods, each with a curved horn, in orange, pink, red, white, purple, or greenish yellow. After flowering the plants form spindle-shaped follicles that split to release flat brown seeds carried on tufts of silky hairs. Milkweeds are the obligate larval host for monarch butterflies, and the nectar-rich flowers draw many other pollinators. All parts contain cardiac glycosides that are poisonous to people, pets, and livestock if eaten. The genus spans habitats from dry prairies to wet meadows, so moisture needs vary by species. Most form deep roots and re-establish slowly after transplanting.

Native Range

Asclepias is centered in North America, where most of its roughly 140 species occur, with additional species in Central and South America and a few in Africa. Many North American species grow in prairies, meadows, and along roadsides.

Suggested Uses

Planted in pollinator and butterfly gardens, native meadow and prairie plantings, and the back or middle of perennial borders depending on height. Wet-soil species suit rain gardens and pond margins, while dryland species suit gravel and naturalistic plantings. The silky seed heads are also used in dried arrangements.

How to Identify

Identify Asclepias by its upright stems that bleed milky latex when broken, opposite or whorled leaves, and rounded umbels of flowers with five swept-back petals and a raised central crown of hoods and horns. The paired spindle-shaped seed pods, splitting to release silky-tufted seeds, are a clear feature in late season. A. tuberosa is recognized by its clear sap and alternate leaves, unlike most of the genus.

Appearance

Size & Dimensions

Height1' - 5'

Width/Spread1' - 3'

Colors

Flower Colors

red

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~5 weeks

Flowers: June–August

Summer

Most milkweeds bloom from early to late summer, with flowering lasting three to six weeks. The flowers are heavily scented in several species and produce abundant nectar that draws butterflies, bees, and wasps. Monarch caterpillars feed on the foliage through the same period.

Detailed Descriptions

Flower Description

orange, pink, red, white, or purple

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-10 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.0 - 7.5 (Neutral to alkaline)

3579

Soil Types

loam sand clay

Drainageaverage

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Grow Asclepias in full sun in soil matched to the species, ranging from the dry, sandy ground suited to A. tuberosa to the consistently moist sites of A. incarnata, at a pH of 6.0-7.5. Most species are drought tolerant once their deep roots establish, and they re-establish slowly after transplanting, so plants are set out young and left undisturbed. Water new plantings until established, then reduce watering for the dryland species. The plants need little fertilizer and can flop in overly rich soil. Aphids, particularly the orange oleander aphid, are the most common pest. Stems and roots release milky sap that can irritate skin and eyes.

Pruning

Cut the stems back to the ground in late autumn or early spring once they have died down. Leaving the seed pods until they split allows self-seeding, while removing them before they open limits spread. Plants need no other pruning through the season.