CUTTINGS; Trying to Curb the Aggressive Milkweed
By PATRICIA A. TAYLOR
Published: August 5, 2001
GARDENERS east of the Rockies who are less than meticulous weeders will invariably find the common milkweed (Asclepias syriaca) in their sunny to partly sunny borders. As children know, the numerous, easily germinated seeds of this plant fly through the air with ease.
Though a native, common milkweed has been classified as a noxious weed by 35 states. To keep it or not then becomes the question for anyone who finds it in a border.
A friend was just about to yank hers out when she saw a swallowtail butterfly land on the pretty, pinkish purple flowers. She let the plant stay. I think she'll regret it.
As with all members of this 200-strong genus, common milkweed is a magnet for butterflies and bees. It also contains toxins that are poisonous to many chewing animals, a factor that helps ensure its survival and keeps its appearance tidy.
But unlike many Asclepias species, common milkweed spreads aggressively. Indeed, roots on established stands have been found burrowing as deep as 12 feet. If a plant stays too long, it may be impossible to eradicate it.
Fortunately, other members of the genus are more restrained, forming clumps while being just as widely attractive to nectar-seeking insects. I have three of them in my New Jersey gardens.
The most widely known is the bright orange butterfly weed (A. tuberosa). It is a key partner, with the monarch butterfly, in one of the most dramatic and inspiring insect-plant relationships to be found.
The plant's chemicals are poisonous to many butterfly predators but not to butterflies themselves. In using the butterfly weed as a food source, the monarch caterpillars store the plant's poisons in their tissues, becoming poisonous to predators in the process. Over time, birds and other insect eaters have learned to avoid both the caterpillars and the butterflies.
Each year, hundreds of millions of monarch butterflies travel from Mexico to Canada and back and breed as they travel. And throughout the journey, the butterfly weed provides them food and built-in protection. While some other milkweeds also offer that protection, none have the orange symbolism.
Perhaps because they are trying to be such good hosts, butterfly weeds bloom from mid-June through August in my gardens. The flat clusters of bright orange flowers crown stems that are between one and two feet tall.
The three- to four-foot-tall swamp milkweeds (A. incarnata) are another favorite butterfly plant. Though found growing wild in moist places, they also do fine in ordinary garden soil. The Latin species designation means ''flesh-colored,'' and the plants usually feature flat spreads of pink to mauve colored blossoms. There's a new cultivar on the market called Soulmate, and its flowers are a deep rose color, which sounds attractive to me.
As it is, I have the Ice Ballet cultivar and chose it for a sunny, all-white border. It blooms for three weeks in July and is covered with bees and butterflies the whole time.
Woodland milkweed (A. exaltata) is a rather unusual member of the genus in that it likes shade. It flowers earlier than others, blooming for two mid-June weeks in my garden. And the flowers themselves are quite different, clustering to form white balls that delicately hang from the top of the stalwart, unbranched five-foot-tall stems.
All three of these Asclepias species produce unusual, canoe-shaped seedpods. The two- to three-inch-tall ones on the swamp milkweed are the most numerous. As many as 10 will curl about in an abstract display where once a flower cluster bloomed.
The woodland milkweed pods are single sculptures at the end of unbranched stems. The pods are four inches long and look as if they are attached to the stem with a ladle. Because of its longer bloom period, butterfly weed does not produce its two- to three-inch pods until Labor Day.
A white, silky thread trails from each seed packed in the pods. This thread is so buoyant that it floats in both air and water. During World War II, it was used in life jackets.
I would like to have many more clump-forming Asclepias species in my garden but they are difficult to find. Purple milkweed (A. purpurascens) is a beautiful two- to four-foot-tall plant with showy rose purple flowers during much of summer. Prairie Moon Nursery sells out of this plant so quickly that it no longer lists it in the catalogue.
The company is also trying to build up its supply of A. hirtella. This 18- to 30-inch-tall milkweed bears pinkish, off-white flowers for a good month in summer and thrives in drought conditions.
But even without these species, my garden offers a continuous supply of nectar to butterflies. And I need not weed out any of the plants to do so.
These nurseries offer a variety of Asclepias:
Prairie Moon Nursery, Route 3, Box 163, Winona, Minn. 55987; (507) 452-1362; free catalog.
Prairie Restorations Inc., Post Office Box 327, Princeton, Minn. 55371; (763) 389-4342; free catalog.
We-Du Nursery, Route 5, Box 724, Marion, N.C. 28752; (828) 738-8300; catalog, $2.
Photos: The bright orange butterfly weed (Asclepias tuberosa), top, is eaten by monarch butterfies; woodland milkweed (Asclepias exaltata), above. (Photographs by Patricia A. Taylor)