Meet the Natives: Common Milkweed, part one

This beautiful photograph of a monarch butterfly on milkweed is by garden blogger Jodi DeLong. Check out her amazing photographs of monarchs emerging from chrysalides here and here.

WANT IT, CAN’T HAVE IT. That’s the tragedy of my relationship with common milkweed, a plant that is beautiful, easy to grow, almost essential for monarch butterflies … and banned in many places, including Nova Scotia, where I live. When I first learned about laws forbidding me to grow this plant, which is so important to the life cycle of a beautiful and threatened butterfly, I was appalled: How could authorities be so backward? Now that I’ve looked into it a bit more thoroughly, I think I’ve come to understand why the laws exist. I still think the laws probably need to be changed, but I now hope more for a compromise than for a complete end to all restrictions.

But before I talk about laws banning milkweed, let me give you some background on the plant.


Common milkweed (Asclepias syriaca) has thick, erect stems that grow quite tall (4-6 feet) and bear 4-inch pompoms of smaller flowers that look pink to me but are sometimes described as mauve, creamy white, or purplish. As is characteristic of milkweeds, the individual flowers have an unusual hour-glass shape, with some petals pointing downward and others pointing up. When injured, milkweeds “bleed” a milky sap—hence the name.

Common milkweed closely resembles swamp milkweed (A. incarnata), which I’ve written about previously (and which, fortunately, is not banned in Nova Scotia). However, the flower clusters of common milkweed are round and carried up and down the stalk, and the plant has coarse foliage; the flowers of swamp milkweed are flat-topped and carried on the top of the plant, and the foliage is more fragile.

Common milkweed flowers from May to August, the flowers being followed by attractive seed heads that are popular with crafters. The blooms are fragrant; the odor has been described as “heavenly” and as being like that of “hyacinths and lilacs.”

By now no doubt you can begin to see why I want this plant so badly! And yet there’s more.

Value to wildlife

The U.S. Department of Agriculture offers us the following enticing quote: “This is a wonderful horticultural plant for landscaping to attract butterflies (particularly monarchs), whose numbers are declining and migratory routes changing due to lack of appropriate habitat.” Monarch butterflies will lay their eggs only on plants in the milkweed family because the plant contains a chemical called a cardiac glycoside, which is mildly toxic and makes the caterpillars and adult butterflies taste bad to potential predators.

Once upon a time, common milkweed was plentiful in the northeastern United States and lower eastern Canada, and monarchs had all the plants their tiny insect hearts could possibly desire. However, development and agriculture have destroyed many of these stands, leaving monarchs and other butterflies with fewer plants to feed on. Today common milkweed is most often found growing primarily in untended fields and pastures, ditches, and roadsides.

Where, at least in Canada, it is often treated as a weed. Yes, sadly this important plant is banned outright in Ontario, Quebec, Manitoba, and Nova Scotia.* In addition, Minnesota allows individual counties to ban common milkweed if they wish to do so, but there is no statewide ban.

The bans in Ontario and Quebec are of particular concern because these provinces are in the heart of monarch breeding territory. Nova Scotia supposedly is on the fringes of this zone, but as Jodi DeLong's photographs attest (see photo above), monarchs definitely do breed here.

Why a Weed?

OK, milkweeds are toxic. But common milkweed apparently is toxic only when ingested in large quantities. (Some of the other milkweeds apparently are more toxic.) And besides, milkweeds taste so bad that animals usually don’t want to eat them. (This is, remember, precisely why monarchs like them so much.) How poisonous is milkweed? The only documented, naturally occurring (that is, not involving nasty force-feeding of the plant to livestock) case I’ve been able to find took place in Maryland during a drought and was recorded in 1942. Evidently some sheep ate milkweed and died, but they ate the plant only because it was the only food available at the time, because of the drought.

Although anyone who wants to ban milkweed will mention its toxicity, the primary reason for banning it seems to be that it causes problem for farmers. As the province of Nova Scotia explains on its website, "Common milkweed is a competitive weed and can absorb nutrients and water more efficiently than many crops. Therefore, it can reduce crop yields significantly. Because of its rapid spread, it can quickly become a nuisance weed on farmland. Once a field becomes infested, it is very difficult to control. At harvest, the thick sap of common milkweed can clog combine parts. The fluffy seed may also clog air intakes."

Of course, farmers have to contend with many weeds. Unfortunately, milkweed is particularly difficult to control. It spreads readily and has deep roots. "Mechanical control of common milkweed, such as cutting or clipping, simply leads to the creation of larger colonies from the rootstocks of the plant," says Nova Scotia, although the province admits that "continuous cultivation will eventually deplete food reserves in the rootstocks." Common milkweed also does not respond to many of the herbicides used today. However, it can be controlled with glyphosate (often sold under the brand name Roundup), which is generally regarded as one of the safer herbicides in use today. (Many people object to all herbicides; I'd like to sidestep this debate if I can today.)

The bottom line, as the province of Ontario explains on its website, is that milkweed "can have a considerable negative impact to a grower's net economic return."

Tomorrow: Part two, alternatives to outright bans, cultivation

* These and other statements made in this post are based on Internet research. I've done everything I can short of making telephone calls to make sure that my information is accurate and up to date.


Anonymous said...

You stated you live in Nova Scotia and Milkweed is banned, I just called Halifax Seed and they stated it is not banned, so enjoy this plant as it is something Monarch's love and hopefully we can help preserve these beautiful butterflies.....

Wild Flora said...

Dear Anonymous,

There are several species of milkweed. Common milkweed is classified as Noxious Weed in Nova Scotia but other types of milkweed are not. (I did say that in the original post.) However, you're right that it's not completely banned here. As a Class One Noxious Weed it is only banned on land from which it is likely to spread to cultivated or pasture land. Unfortunately this does mean that it would be prohibited on my property but perhaps not if you don't live near a rural area? Thanks for bringing this mistake to my attention!