Weeds with purpose

Though many gardeners consider them little more than weeds, milkweeds are essential to much-loved monarch butterflies.

Last update: October 14, 2009 - 10:11 AM

Q I've read that monarch butterflies need milkweed to feed on. What kind of milkweed? Where can I plant it?

A Milkweed plants -- members of the genus Asclepias -- are necessary for monarch butterfly larvae. Adults monarchs lay their eggs on milkweeds. Once those eggs hatch, the larvae feed on the leaves until it's time to develop into pupae. When butterflies emerge from the pupae, they feed on nectar from milkweed flowers. They also suck nectar from many other flowers, including Mexican sunflowers, zinnias and other plants with daisy-like blossoms.

Common milkweed (Asclepias syriaca) and swamp milkweed (Asclepias incarnata) are both excellent plants for attracting and feeding monarchs. They can be started easily from seeds indoors or sown directly into the garden. All milkweeds thrive in full sunlight. Swamp milkweed grows best in relatively moist, fertile, well-drained soil. It grows about 3 feet tall and produces clusters of tiny, fragrant flowers ranging in color from white to pink or light purple.

Common milkweed can grow in poorer soil. Plants usually grow 2 to 3 feet tall, though occasionally they can reach as high as 5 or 6 feet. Because common milkweed is aggressive (it spreads through vigorous underground rhizomes as well as seeds), it's best planted where there is lots of space. However, you can reduce their spread to some degree by removing seed pods before they burst and disperse their seeds.

The native flowering perennial called butterfly weed (Asclepias tuberosa) also is a favorite of monarchs. It can be grown in a sunny, well-drained garden. It's more compact that other Asclepias and produces vivid orange or golden-colored flowers.

Deb Brown is a garden writer and former extension horticulturist with the University of Minnesota. To ask her a gardening question, call 612-673-7793 and leave a message. She will answer questions in this column only.

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