Natural Notes: Milkweed or not a weed?

"Is that a weed?  How about that one?  Or that one??"  This is a question I have heard countless times from plot renters at the Taylor Street Farms urban garden in Chicago.  What exactly is a weed?  And how does one know what is considered a weed and which is not?  Are humans just arbitrarily biased against some plants, and subsequently do we just label things a weed when we don't like it?

The confusion arises from the fact that there are actually two definitions of "weed" in this context (ignoring a deviant third definition, of course).  One definition of a weed is any plant that is considered undesirable.  Dandelions (Taraxacum officinale) are great examples.  Ugh, who wants those ugly yellow flowers disrupting a lush green lawn?  And they're impossible to get rid of it seems!  This definition of a weed is inherently biased, as the very same plant could be considered by others as a prized botanical specimen.  In many parts of Europe, for example, Dandelions are highly valued for their ornamental and event culinary attributes.  Some more progressive plant and garden enthusiasts have suggested the idea that we should do away with the word weed altogether in acknowledgement of our sometimes misguided animosity towards "weeds."

But there's another definition of a weed, and for that one we must look to nature.  In wild plant communities, such as prairies, oak savannas, and other plant communities found within the greater Chicago Area, each plant has a different relationship with its surroundings, or what biologists refer to as its niche.  In natural ecosystems, the type of plants that grow in certain places grow there based upon factors such as amount of sunlight, type of soil, climate, amount of disturbances from wind or water, and other living and non-living factors.  Some types of plants are very particular about their growing needs, while others are more opportunistic or general and can tolerate less ideal growing conditions.  Also, some plants produce more offspring than others (more seeds).   Plants that can produce lots of seedlings and which can grow in compromised locations rapidly and in great abundance, from an ecological standpoint, can be referred to as weeds.  

 So what's a weed and what's not depends upon what definition is being used and in what context.  Allow me to introduce you to a group of plants that are both weeds and not weeds (depending on the situation) but are nonetheless ecologically important native plants in the Chicago region:  the Milkweeds (Asclepias spp., figure 1).

Figure 1:  Common milkweed in bloom in a natural prairie in a forest preserve about 30 minutes from downtown Chicago.  

Milkweeds are common wildflowers in Chicago, and are most noted for their associate butterfly, the beautiful and graceful Monarch Butterfly (Danaus plexippus).  Monarch butterflies (figure 2) rely exclusively on Milkweeds for their life cycle (egg, caterpillar, pupae, and adult, see figure 3).
Figure 2:  Female monarch butterfly. 
Photo credits:  Kenneth Dwain Harrelson
Figure 3

Although adult monarchs will drink nectar from other flowers, no other plants besides Milkweed will support their life stages.   But monarchs are not the only animal that relies on Milkweed to complete its life cycle.  In fact, there are dozens of other insects that live on milkweed plants, including aphids, ants, other butterflies, and bright red milkweed bugs (see figure 4) to name just a few.  In essence, a single milkweed plant can be considered a mini ecosystem in itself!
Figure 4:  Red milkweed
bugs mating

At Taylor Street Farms, milkweed is a common sighting along the edges of the garden.  What milkweeds can be found, and which ones are considered 'weeds'?

In northern Illinois, there are over a dozen different species of native milkweed.   At the Taylor Street farms there are only three different species present:  Common Milkweed, Butterfly Weed, and Swamp Milkweed.  Allow me to introduce you to these three important and showy wildflowers.







Common Milkweed (A. syriaca)
Figure 5
This milkweed (shown in figures 1 & 5) by definition (ecologically) is a weed.  Common in open and dry sunny areas along roadsides, meadows, and even waste places, this large and tall (up to 4') broad-leaved wildflower is usually the first milkweed to bloom, with flowers typically blossoming in late June.  The flowers grow in an excurrent form giving them a ball-like appearance.  Common milkweed spreads by rhizomes, or underground roots, and so what might look like 20 or more individuals might actually be just one plant!  This plant can spread and grow quickly in spite of the complaints of some farmers or gardeners, but Monarch Butterflies complain not!




Butterfly Weed (A. tuberosa)
Figure 6
Butterfly Weed does not look like your typical milkweed with its bright orange flowers.  This lower-lying plant (usually not much taller than a couple of feet) grows in dry prairies and sand dunes and does well in an open sunny garden.  The leaves are more lance-shaped (thinner) and the flowers bloom a little bit later than Common Milkweed.  Butterfly weed is a magnet for Monarch Butterflies and all other milkweed associates. You will find some of it growing in the native wildflower area on the north exterior of the Taylor Street Farms urban garden.  Butterfly weed, once established, will spread very slowly and is considered a "better-behaved" wildflower.



 Swamp Milkweed (A.  incarnata)
Figure 7

With a bright pink cluster of flower and with pointy leaves, this tall and elegant milkweed is a native of wet and damp places, but can easily grow in more moderate conditions.  The leaves are bluntly pointed at the tip and the clusters of flowers grow as an umbel at the top.  At Taylor Street Farms it can be found in the native wildflower area in the north exterior of the garden.  Again, this plant spreads very slowly and is unlikely to be considered a weed.



Figure 8:  Milkweed seeds.  Photo credits:  Unknown
After milkweeds are down flowering, seed pods will form which will eventually dry and release seeds (figure 8).  Each seed has a cotton-like filament that allows wind to carry them for dispersal.  In order for the plant to release seeds, they must be exposed to the cold, drying winds of Autumn. 









So the next time you are weeding in your garden, consider spreading some milkweed seeds.  Not all milkweeds are weeds, and these native wildflowers are supposed to be here anyways.  You will also be rewarded!  A monarch butterfly might just land in your garden to thank you as you improve the health of our urban green spaces.
























































































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