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Tales from a Plant Addict

Fun (& a few serious) facts, tips and tricks for every gardener, new and old.

Milkweed-- Asclepias spp.

I will admit, some of my best garden plants started out by pure luck and maybe a dash of laziness. Caring for my young son means I don't have the time to weed the garden as often as I probably should. Last summer, a large plant appeared in my garden next to our patio. Initially, I wasn't sure what it was. As it quickly grew, I realized it was common milkweed, Asclepias syriaca. My husband wanted to tear it out, because he considered it a weed and he was worried it would spread everywhere. I wanted to give it a chance. Milkweeds are a great native plant to use for attracting pollinators, those creatures, particularly insects, that transfer pollen between flowers to help produce much of the fresh produce we consume.

Pollinators, whether birds, bats or insects, are a hot topic these days, and for good reason! The activity of pollinators is responsible for somewhere between one in every three to four bites of food and drink we consume. According to the USDA, over 80% of the world's flowering plants depend on pollinators to produce fruit and seeds.

The milkweed plant grew to about five feet high last year, and produced three stems, each topped with clusters of light pink flowers. Typically milkweed does not flower the first year from seed. So what I saw in my garden last year was likely the second year of growth for the plant. I have no recollection of seeing this plant the year before—but my son was a newborn that summer, so what was going on in the garden during that time is pretty much a blur!

The individual flowers have five petals and are only about half an inch long, but occur in large clusters called umbels at the top of the plant and at the base of the upper leaves. While each flower is perfect, meaning they have both male and female structures, they must be cross pollinated in order to produce seed. I didn't notice it until this year, but the flowers definitely have a pleasant fragrance. This fragrance and the flowers' sweet nectar attract many different insect pollinators to a given plant.

Each flower has a unique structure where the pollen is housed inside a narrow opening in the flower. When an insect lands on the flower, its legs slip inside these narrow openings and emerge with tiny pollen sacs attached. Ideally, the insect flies to another milkweed plant and deposits the pollen on that plant's flowers. Unfortunately this process is not always successful. Some insects get stuck and end up leaving a leg behind or even die in the flower.

Somewhere between one and five flowers per umbel of flowers will be successfully pollinated. These flowers transform into a squishy green seed pod called a follicle. In late summer and fall, these follicles turn brown and split, revealing neatly arranged rows of seed, each with a silky fiber attached to help it take flight and disperse via the wind.

Some farmers will probably think I'm nuts to grow milkweed on purpose. Milkweed's ability to spread via deep underground roots allows it to send up new plants near existing ones, or some distance away. For the relatively small space that is my backyard, I had a few new plants try to emerge in less than desirable locations, but they were easy to pull. On the much larger scale of a farm field, milkweed can wreak havoc on fields of crops if allowed to establish, because its roots are deeper than any plow can reach.

While some farmers despise milkweed, some farmers are growing milkweed for commercial applications as a source of hypoallergenic fiber from the seed pods, and oil pressed from the seed. During WWII, milkweed fiber was used as filler for life jackets when other fibers were in short supply. Today, the Monarch Flyway company of Ogallala, Nebraska manufacturers high-end pillows and comforters that contain milkweed fiber, which reportedly have a higher insulating value than goose down fibers. More locally, Western Illinois University has explored potential economic uses for milkweed and other plants as part of its "Alternative Crops Research Program".

Milkweed is named for the milky sap that exudes from any cut portion of the plant. The sap contains various toxic compounds, many of which are poisonous to livestock if enough is consumed— another reason for farmers to like the plant even less. It is the primary food source for monarch butterfly caterpillars, which themselves assimilate the toxic compounds and in turn end up toxic to any predators that might want to eat them. Adult monarchs consume nectar from the flowers and act as pollinators.

Eradication of milkweed from agricultural lands on a large scale thanks to nonselective herbicides like glyphosate has resulted in a dramatic drop in numbers of monarch butterflies—the population has declined by about 90 percent in less than 20 years. In 1996, there were estimated to be approximately one billion monarch butterflies. By 2013, their numbers diminished to 33 million. In 2014, the U.S. Fish and Wildlife Service requested that the Monarch butterfly be added to the Federal endangered species list.

A movement is underway to encourage development of monarch "waystations", where milkweed is deliberately planted. Read more at . Common milkweed is the favorite foodstuff of monarch larvae, but they will eat other Asclepias species as well. A few to consider:

  • Swamp Milkweed (Asclepias incarnate)—Native to North American wetlands; prefers damp to wet soils
  • Purple Milkweed (Asclepias purpurascens)—Native to the Eastern, Southern and Midwestern U.S.; similar to common milkweed but has purple flowers
  • Butterfly Weed (Asclepias tuberosa)—Native to Eastern North America; narrow leaves and orange flowers; prefers dry soils
  • Poke Milkweed (Asclepias exaltata)—Native to Eastern North America; white flowers; good for shady areas

Whether you are intending to support pollinators like monarch butterflies or not, milkweed is a great low maintenance choice for the garden. They are well adapted to our local environment and require very little additional watering or other special care once established.

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