As I write this in mid-June, the Butterfly Milkweed in my southwestern Ontario garden is just starting to get an orange tinge to the flower buds. This brilliant orange flower loves sun and sand and its tuberous root (from which it gets its specific epithet – tuberosa) makes it a great drought tolerant choice for the garden. A favourite of butterflies, bees, wasps and other insects, no sun-drenched garden should be without it. Plant Description and In the Garden sections, below, are courtesy of Shaun Booth of In Our Nature.
Common Name: Butterfly Milkweed
Scientific Name: Asclepias tuberosa
Family: Asclepiadaceae (Milkweed Family)
Alternate Common Names: Butterflyweed, Chigger Flower, Orange Milkweed, Pleurisy Root
Plant Description: Butterfly Milkweed is characterized by rigid, hairy stems with lance-shaped, alternate leaves attached with little to no leaf stalk. Leaves measure about 5-15cm long and 2.5cm wide and are toothless, glabrous on top, sparsely hairy underneath and end with a pointed tip. Only the foliage exudes a milky sap. Stems are mostly unbranching except for at the top where several flat-topped flower clusters, up to 8cm across, can be found. Each cluster is made up of up to 25 individual flowers measuring about 1cm across. Flowers are characterized by 5 hoods with a curved horn emerging from each one and arching towards the central crown. Each flower has 5 backwards flared petals. Flowers give way to narrow, smooth, 15cm long seed pods. Each pod contains numerous flat brown seeds with tufts of white silk that allow them to be carried by the wind.
In the Garden: Butterfly Milkweed is valued in gardens for its cheerful orange flowers, long bloom time and high drought tolerance. It maintains a clumping form and is not an aggressive spreader which makes it suitable for small or formal gardens. The deep taproot makes it hard to transplant, so choose its location wisely. Stems remain upright well into the winter months.
Skill Level: beginner
Exposure: full sun – not shade tolerant
Soil Type: prefers sandy or rocky soil that is well-drained
Moisture: dry to medium
Height: 80 cm
Spread: 45 cm
Bloom Period: Jun, Jul, Aug
Fragrant (Y/N): N
Showy Fruit (Y/N): N
Cut Flower (Y/N): Y
Pests: no serious insect or disease problems, though crown rot can be a problem in wet, poorly drained soils and it is susceptible to rust and leaf spot.
Natural Habitat: prairies, open woods or on roadsides
Wildlife Value: nectar source for native bees, butterflies and hummingbirds
Butterfly Larva Host Plant For: Monarch butterfly (Danaus plexippus), Grey Hairstreak (Strymon melinus), and Queen butterfly (Danaus gilippus)
Moth Larva Host Plant For: Unexpected Cycnia (Cycnia inopinatus), Delicate Cycnia (Cycnia tenera), Milkweed Tussock Moth (Euchaetes egle), Stalk Borer Moth (Papaipema nebris), Isabella Tiger Moth (Pyrrharctia Isabella), Striped Garden Caterpillar (Trichordestra legitima)
USDA Hardiness Zone: 3-9
Propagation: Seeds sown in the spring require 30 days cold stratification. Plants are easily grown from seed, but are somewhat slow to establish and may take 2-3 years to produce flowers. Butterfly Milkweed does not transplant well due to its deep taproot, and is probably best left undisturbed once established. The quickest method of propagation is root cuttings. In the fall, cut the taproot into 2-inch sections and plant each section vertically, keeping the area moist.
Additional Info: Unlike many of the other milkweeds, this species does not have milky-sapped stems. Asclepias tuberosa will host monarch butterfly caterpillars but if other milkweeds are present this one is often ignored.