The milkweed species is so crucial to the life cycle of the monarch butterfly that monarch butterflies and their relatives, such as queens and tigers, are called “milkweed butterflies.” In Britain, the Monarch is simply called The Milkweed.

The monarch butterfly is distributed throughout the United States and Canada, but is limited to the Pacific Northwest unless there is a long, warm summer. Monarchs are famous not only for the beauty of their tiger-colored wings, but also for their multigenerational migration to Mexico, where they overwinter. Sometimes the trees are so full of Monarch butterflies that even the heavy branches break off. Monarch butterflies are also known to be one of the rare insects that cross the Atlantic Ocean.

The Monarch is found almost everywhere in its range, including meadows, gardens, parks, and roadsides. Fortunately, milkweed plants also find these habitats to their liking.

Monarch butterflies use milkweed as a source of nectar and as a host plant for their larvae. After mating in the spring, the female lays her eggs on the leaves of milkweed plants. The eggs hatch and the black, yellow and white striped caterpillars eat their own egg box for a burst of energy, then begin to eat the milkweed. Milkweed not only provides food for the caterpillar, but also toxins called cardenolides, which make both the caterpillar and the adult butterfly unpleasant to potential predators. After about two weeks, the caterpillar turns into a chrysalis. The monarch’s chrysalis is extraordinarily beautiful. It is pale jade green with spots of what looks like gold paint. After about two weeks, the butterfly emerges. Monarch butterflies live between one and seven months, depending on the time of year they are born.

There are more than 140 species of milkweed, including the common milkweed (Asclepias syraica), tropical milkweed (Asclepias curassavica), and swamp milkweed (Asclepias incarnata). The flowers can appear in shades of white, pink, mauve, orange, yellow, or scarlet. The common milkweed is a perennial that grows in full sun, but can also tolerate some shade. It can be invasive and is considered a weed in many areas. The flowers, which grow in umbels, appear in late spring or early summer. The seeds are famous for having long parachutes made from pappus or dental floss. They sprout from showy seed pods and are blown away by the wind. Pappus has been shown to have such good insulating qualities that it is now used to fill pillows.

The common milkweed can grow three to six feet tall. It spreads through rhizomes. Marsh milkweed is non-invasive, prefers slightly moist soil, and can be found on the edges of freshwater bodies. The flowers bloom later than the common milkweed. Butterfly grass (Asclepias tuberosa) has orange flowers and grows up to a meter in height. It also needs full sun and is a popular garden plant.

All milkweed exude a milky sap that gives them their name. This sap irritates the skin and milkweeds are considered poisonous to humans. However, in ancient times, milkweed was prized for its medicinal properties. In fact, the species is named after Asclepius, who was the god of healing in ancient Greece. The sap, while irritating in itself, is still used to treat poison ivy.

Gardeners who want to grow milkweed plants to attract the monarch should know that they do well in Zones 4 to 10. They are excellent in prairie and border gardens. Butterfly grass can tolerate drought, and common and tropical milkweed plants need an average amount of watering.