key growing information

Growing Butterfly Weed (Asclepias)

Growing butterfly weed and other asclepias from seed: germination, cold treatment for pleurisy root, avoiding root-bound transplants, spacing, sun, soil and cutting.

By Hensley’s Seed Co. September 3, 2026

Asclepias (Butterfly Weed) - Key Growing Information

Asclepias flowers, also known as butterfly weed and pleurisy root, in full bloom.

DAYS TO GERMINATION:

Expect 14–21 days at 65–70°F (18–21°C). Pleurisy root alone needs a cold treatment first: moisten the seed, cover it with plastic and refrigerate at 40–50°F (4–10°C) for 7–14 days, then move it somewhere warmer to sprout.

SOWING:

Transplants are recommended. Start seed 1/4" deep in seed-starting mix 7–9 weeks before the last frost. Seedlings begin sending down a taproot right away and decline quickly if they ever become root-bound, so pot them up into bigger cell packs or 3–4" pots 3–5 weeks after sowing. Harden them off and plant out after the last frost. Seed can also be sown directly outdoors in fall or spring.

LIGHT PREFERENCE:

Full sun.

PLANT HEIGHT:

Depends on species.

PLANT SPACING:

12–24" apart.

HARDINESS ZONES:

Depends on species.

HARVEST:

Cut when one-half to two-thirds of the flowers are open. Stems that wilt after cutting usually recover if left in water for 24 hours. Caution: the milky sap can irritate skin and eyes.

SOIL:

Sandy loam or even lean soil, as long as it drains well.

USES:

Cut flowers, borders, containers and pollinator or butterfly gardens.

SCIENTIFIC NAME:

Asclepias spp.