Articles > Plant Profiles
Milkweeds - 1/15/2015
by Jim Becker
Asclepias inarnata A. speciosa A. syriaca A. currasavica
Never has there been a more attractive and useful group of weeds than the milkweeds, more than 100 species belonging to the genus Asclepias and distributed mainly throughout North America and parts of southern Africa. Most are straight-stemmed herbaceous perennials, but a few are shrubs, like Asclepias physocarpa, that can grow 12 feet tall. The leaves vary from impressively large, broad, and woolly to threadlike and smooth. Some species have silky smooth pods; others, warty or spiny ones. Inside each pod are numerous seeds, each with a tuft of long, silky hairs. When the pods split open, the hairs act as little parachutes. Anyone who has played with milkweed pods as a child remembers the silky down and the gently rising seeds.
The common name “milkweed” comes from the milky latex that exudes when a milkweed plant is wounded. Contact with the latex irritates the skin of some people, but it benefits the plant by deterring munching by herbivorous animals. The generic name Asclepias honors Asklepios, the Greek god of medicine, so highly did Native Americans and European settlers value milkweeds as medicine.
One of the great charms of milkweeds is their associations with insects. A clump of milkweed in bloom is a great attraction for nectaring bees and butterflies, especially the Monarch, which lays its eggs only on Asclepias species. The small green eggs of the Monarch hatch forth exquisitely striped caterpillars. As they feed on the leaves, they develop the bad taste that protects them. Kids love caterpillar watching, so take some time off and enjoy their munching.
The numerous, showy, and often scented flowers are usually borne in clusters called cymes, either at the ends of the stems or in the leaf axils. They are ingeniously adapted to pollination by insects. At the top of every flower is a crown of five pouches, or hoods, each containing an enticing stash of nectar. As an insect alights on a flower, its legs are guided down into grooves, where one of its hairs or claws catches on a structure connecting two waxy masses of pollen called pollinia. The insect flies off to another flower, then browses among its hoods for nectar and dislodges the pollinia, which then pollinate the second flower.
Besides medicine, milkweeds have also traditionally been used as fiber and food. Though generally considered to be toxic plants, the tender young shoots, leaves, flower buds, and seedpods of Asclepias syriaca, the common Eastern species, when properly prepared by repeated blanching, are edible, even tasty. Native Americans used the silk, or floss, to line their children’s cradles, and Europeans wove it into fabric. The silks are too short to be easily spun into thread alone, but they add sheen and strength when blended with cotton and flax. Though tedious to collect (it takes several hundred pods to yield a pound of floss), tests have shown that milkweed floss has the same density as goose down and is an even better insulator. During World War II, schoolchildren were encouraged to collect bags of floss to be used as stuffing for life jackets in place of kapok, which was not available. The USDA studied the commercial production of milkweed fiber in the early part of 1900’s, but few farmers gave it a try.
Useful as these weeds are, most are also very attractive in the garden. Many, like A. speciosa and A syriaca, are handsome, even stately plants and are great as single specimens in the perennial border. Like most milkweeds, they prefer a well drained soil. The butterfly weed (A. tuberosa) and swamp milkweed (A. incarnata), look best in massed, colorful plantings or in large clumps. The butterfly weed is one of our favorite milkweeds. It is short lived in wet soils, but it is worth the effort for its magnificent swatch of pure orange which is unmatched by anything except the Monarch Butterfly that feeds on it. One of the few milkweeds that prefers a wet area is A. incarnata. It is called swamp milkweed, but you don’t need a swamp to grow it. It does well in the evenly moist soils found in most perennial gardens. Most species are hardy down to USDA Zone 3 and all are great additions to natural plantings and wildflower meadows.
We grow about15 different milkweeds at our nursery, Goodwin Creek Gardens, and have found all to be easily propagated by seeds. We collect the seeds as the pods begin to split open in fall and their ripe seeds are dark brown in color (immature seeds are green). We remove the seeds from the pods, dry them in paper bags and then store them in airtight containers. Seeds can be planted in spring or in pots during winter to be transplanted outdoors a few weeks later. Some milkweeds can also be divided, including A. syriaca and A. verticillata. To say they are easily dividable is an understatement. They spread quickly by underground runners, so give them a lot of room to run.
Most milkweeds die back each winter to underground buds and rhizomes and emerge very late in the spring. Mark the location of plants by leaving last year’s dead stalks in place until the new growth appears. The tall stems and their pods also add interest to the winter garden.
Stands of milkweeds are necessary for the survival of Monarch butterflies. Unfortunately, milkweeds are often killed by roadside maintenance crews and hay farmers. Most livestock leave milkweeds alone, or they eat only the tender new shoots. If you want to spread milkweed in wild places, however, be safe and encourage it away from hay fields and pastures. There are plenty of sunny, unused places that can welcome the addition of these most beautiful of weeds.
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