Milkweed perennials (Asclepias spp.) Bear many little star-shaped flowers and produce a milky sap; they’re named for this sap. The plants develop in U.S. Department of Agriculture hardiness zones 3 to 10 and bloom in summer, posture their flowers in wide, flattened clusters at the branch tips. All varieties produce silky seeds in inflated seed pods. Milkweed thrives in a sunny location with sandy soil and offers benefits to insects.
Common milkweed can grow up to 6 feet tall with big 4- to 10-inch-long leaves, occasionally with red veins. Some varieties produce clusters of drooping pinkish-purple flowers, though other varieties’ flowers vary in color from red and yellow-orange to orange and bicolored blooms. All varieties produce green seed pods that turn brown prior to releasing and opening fluffy seeds. All pieces of milkweed plants are toxic if eaten.
Milkweed seeds can easily be spread by the end, which catches the fluffy seeds and also carries them long distances. You can collect the seeds following the pods dry and before they split and release seeds. Sow these seeds in spring or fall, in light, sandy soil if at all possible, and cover lightly with soil. You can also lift and separate existing plants in spring. Lifted plants may not bloom the first year, but expect plants started from seed to bloom the first year.
Milkweed requires little care, as they can grow in any good garden soil, even though they prefer sandy soil. The plants do not need fertilization; they spread freely by underground rhizomes and will quickly take over an whole area. Because of their drought tolerance, some varieties — such as butterfly weed (A. tuberosa), that grows in all USDA zones as an annual — make great plants to utilize xeriscaping.
While the milky sap of these plants is toxic to humans, it is beneficial to your insects. The plants’ flowers attract butterflies, moths, bees and other insects which feed to the plant nectar; the nectar isn’t poisonous, so it does not damage these insects. The caterpillar of the Monarch butterfly eats the leaves of the milkweed plant, which include exactly the exact same poisonous substance since the sap, cardiac glycosides. This poison does not harm the caterpillar; instead it enters the caterpillar’s body, which makes it poisonous to its predators. Even adult Monarch butterflies have this poison in their bodies.