Date Published: January 20, 2003

Common milkweed is a perennial plant with a straight, sturdy, hollow stalk which grows from 90 to 150 cm tall. Leaves are arranged in opposite pairs on the stalks, 10-15 cm apart. Leaves are broad and oblong (7.5-25 cm long, 5-12 cm wide) with rounded ends and smooth edges, coming to a point at the tip. Leaf undersides are paler green than upper leaf surfaces, and are covered with fine hairs. All parts of the plant exude a milky sap when damaged.

Flowers range from almost white through varying shades of pink, and have a pleasant fragrance. The flowers form a spherical shape called an umbel with flowers (10 mm long) occurring at the ends of stems. Each flower has five petals. Bees and wasps pollinate the flowers and are often seen around milkweed plants.

Large (12 cm long) seed pods, called follicles, form after flowering and help distinguish milkweed from similar plants. They are pale green and covered with soft bumps. The follicles dry up, turn brown and then split lengthwise in the late summer, releasing brown seeds with a tuft of hair on each which carries it in the wind. Seeds remain viable for up to seven years in the soil.

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Common milkweed is native to eastern North America and was previously known as wild cotton, Virginia silk, and silkweed. Various parts of the plant are edible, including the flowers, young sprouts, and buds. The native peoples of North America have long used this plant for food and used its extract as a medicine for coughs. The fluffy seeds have been used to stuff mattresses and pillows by early settlers. In World Wars I and II, seed was used to stuff life preservers and flight jackets. Milkweeds (Asclepias spp.)are favoured as a food source for the monarch butterfly larvae. Swamp milkweed (A. incarnata L.) is present in Nova Scotia as well.

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Life Cycle

Common milkweed is a perennial which spreads quickly by its windborne seed and its creeping perennial rootstocks. Plants originating from seed, flower in their second season of growth. Plants produce a large number of seed, up to 450 seeds per pod. The perennial roots form a large underground network spreading out from the original plant. In spring, root buds push through the soil to become new plants which flower and set seed.

Common milkweed prefers fertile, well drained soils. Excessive moisture is harmful to this weed. Mature plants can survive drought conditions for a short time. It prefers to grow in areas receiving no less than 30 per cent sunlight, and will grow in full sun. Common milkweed is most often found along roadsides, fencerows, or railways, as well as on wastelands, river basins, and in cereal and forage crops.

Common milkweed is found primarily in Kings County in Nova Scotia, but has also been found along railway lines in other counties.

Common milkweed is a competitive weed and can absorb nutrients and water more efficiently than many crops. Therefore, it can reduce crop yields significantly. Because of its rapid spread, it can quickly become a nuisance weed on farmland. Once a field becomes infested, it is very difficult to control. At harvest, the thick sap of common milkweed can clog combine parts. The fluffy seed may also clog air intakes.

Common milkweed is highly toxic to poultry. Poisoning and death of sheep and cattle have been reported, however, livestock generally avoid eating milkweed.

Mechanical control of common milkweed, such as cutting or clipping, simply leads to the creation of larger colonies from the rootstocks of the plant. Continuous cultivation will eventually deplete food reserves in the rootstocks.

Various herbicides are recommended for control of common milkweed. Glyphosate is recommended when the weed is in the bud to bloom stage. Triclopyr has also been used successfully in non-crop areas to control common milkweed in Nova Scotia. For further information on using these herbicides or for application rates, consult your weed inspector or consult the most recent Guide to Weed Control (Publication 75).

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