A Thorny Question

By Linda Ray

Bull Thistle blossom with fritillary

Last summer a new plant emerged in an overgrown corner of my flower garden. I let it be. This summer a giant six-foot thorny presence re-emerged and then grew to dominate the space like a sentinel keeping guard on the garden; it’s a bull thistle (nicknamed “The Bull”). In full bloom as I write now, it is formidable, beautiful, a bit scary, and all aflutter with pollinators. Having never been up close and personal with a thistle before, I felt it deserved respect and closer scrutiny.

Bull thistle (Cirsium vulgare) is a biennial plant native to Europe and Asia which has now spread over North America. It is the Scottish national flower, a symbol of strength and resilience clearly seen in how its defenses, seed dispersal, and survival on poor soil have allowed it to thrive.

It is an edible weed; leaves, stalks and unopened flower buds can be eaten after careful preparation. It has been used as an anti-inflammatory for treating joint pain. The down from the seed pods was historically used to stuff pillows and to line boots for warmth. This garden thistle now has 50 or more buds which are blossoming into 1- to 2-inch purple flowers that provide a copious amount of nectar for pollinators such as monarchs and other butterflies and a variety of bees. The seeds provide food for birds such as goldfinches and nesting material as well. It is a stunning plant for human eyes to enjoy.

Bull Thistle seed pods captured

On the other hand, it is an aggressively spiny plant which serves it well defensively. When unchecked, it reduces grazing areas by forming dense stands and then crowds out native thistles and other plants (like milkweed and goldenrod) that are necessary in a natural ecosystem. The bull thistle leaches the soil of nutrients and can produce and release biochemicals which cause harm to other plants (a process known as allelopathy). Its thousands of seeds float in the air and down waterways with ease, germinating the following spring. Bull thistle is deemed an invasive or “noxious” species in Maine. The Bull has a scrappy will to live; it is no hot house flower.

Now I find myself questioning my options regarding this thistle. A plant that contributes positively to a healthy biodiversity in one place can certainly be harmful somewhere else. With all the environmental changes happening now, some invasives may fill a niche that provides food and habitat in disturbed places. It is my novice approach to at least consider how a species contributes and balances (or not) a current ecosystem.

Plants just live. Being stewards of them is up to us. Here’s my plan. Having watched and enjoyed The Bull’s two-year life span, I will gather each seed head as the flowers become no longer useful to pollinators and before seed dispersal. This will allow me to continue to enjoy my garden sentinel while ensuring that it does not propagate in my field or my neighbor’s. Now to figure out how to winnow the seeds so I can feed them to our resident goldfinches.

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Sources:

• https://www.nps.gov/articles/000/canada-and-bull-thistles-acadia.htm#:~:text=While%20bull%20thistle%20lives%20for%20just%20two%20years,can%20produce%20millions%20of%20seeds%20in%20their%20lifetime.

  
  

• https://xerces.org/publications/guidelines/native-thistles-conservation-practitioners-guide