I used to think that tropical-looking burdock would be great as the star in a garden of pest and drought resistant, edible, native and naturalized plants. Then I found out what happens when burdock gets out of control.
Common burdock: Burdock is a member of the composite (daisy) family, like its roadside companions, chicory and dandelions. There are at least three kinds of burdock present in North America, all Eurasian imports. The best know is the “common” or “lesser” burdock (Arctium minus), which is pictured in this article. Common burdock has flower stalks rising knee to shoulder height. Common burdock is reported to be found in all providences of Canada and all parts of the USA mainland except Florida and, perhaps, some areas near the Great Lakes. I believe that it has also found its way into Mexico.
Great and woolly burdock: Also naturalized are the great burdock (Arctium lappa), and the less-weedy woolly burdock (Arctium tomentosum). The great burdock has towering flower stalks up to an amazing 9 feet. You can tell great burdock from the “common” form by the size, and by the arrangement of the flowerheads. The great burdock‘s flowerheads are arranged in flat-topped clusters at the top of the stems. The woolly burdock has fleece on the outside of its flowerheads.
Japanese gobo: Lastly, in the vegetable garden and truck farm, there is gobo, the Japanese cultivated version of great burdock.
CULTURE AND REPRODUCTION
Growing conditions: Burdocks like sun or part shade, and any type of soil, as long as it is well-drained. Burdocks have long-tap roots that hold about half the biomass of the plant, up until flowering time, making the plants seriously drought resistant.
Burdock is a biannual. Under ideal conditions, burdocks are bi-annuals, forming a basal rosette (low circle) of leaves the first year, and then dying after they flower in their second summer. A 1994 University of Manitoba study by Norm C. Kenkel and Kelly Graham, however, indicates that if conditions aren’t ideal, common burdock will remain in its immature stage for up to 5 years. The flowers, of course, are followed by the notorious seed-burs.
Burdock spreads only by seed: The seeds are definitely spread via the hooked burs hitch-hiking on passing birds, humans, and furry critters. It may also be that birds eat and spread the seed. However, while there are innumerable reports of birds roosting on burdock, eating the seeds, and using the seed fluff for nesting, there are some reports that burdocks seeds may be poisonous to some birds. Further, while burdock pops up under bird-roosting places, I haven’t found any studies that confirm that the seeds are spread via bird-gut. It is said that it took common burdock some 200 to 300 years to spread to the West Coast, a slow creep which would be more likely if the seeds had to hitch-hike, rather than fly, at least most of the way.
Burdock needs infrequently distributed soil. Burdocks are normally found along roadsides, barnyards, fence lines and the like where the soil has been disturbed. The disturbed soil allows the burdock seeds to germinate and the seedlings to get a foothold. The period of disturbance has to then followed by a period of non-disturbance long enough for burdock to complete its multi-year cycle and make more seeds. Lastly, more disturbance is need for the new seeds to get going. Thus, burdock’s spread is inhibited by its need for once-in-while disturbed earth. Burdock can’t get established in undisturbed areas, in fields that are tilled every year or in areas that are mowed too frequently to allow the plant to flower.
Burdock as an isolated planting: Because of the special needs of a bi-annual that spreads only by seed, common burdock often occurs only as a isolated plant or two. When confined to isolated plantings, as it is usually is in the sub/urban environment, burdock “plays nicely with others” and is not in the same class as mugwort which crowds out almost everything in its path. In the ‘burbs, burdock is not generally as harmful to the environment as the sub/urban sprawl itself, and, in many ways, is just a part of the sprawl.
Burdock as a dominant species: Unfortunately, when conditions are ideal, common burdock also occurs in large patches. The University of Manitoba study was occasioned by common burdock becoming the “dominant understory species” in the Manitoba Delta Marsh area. I’ve been told that the area is open woods, with enough sun for burdock. (I wonder: what provided the necessary occasional disturbance of the earth? Could it have been the good ol’ white tail deer?)
HAZARDS OF COMMON BURDOCK:
Burdock is considered “low risk” by the poison centers, but tell that to human parents and animal caretakers. The burs can cause serious injury if they get in the eyes or are ingested (very rare). Mostly, they’re just very difficult to get out of hair and fur. (I once suffered a major haircut after crawling through a mess of them.)
Common burdock is a bird-killer!!! Now, here’s the bad part: there are several reports on the Internet of hikers finding the dead bodies of small birds such as goldfinches, kinglets, and hummingbirds that became trapped in burdock burs and then died of starvation and exposure. See an eyewitness report on the site of my colleague, Walter Muma.
When I first read about the bird-killing on Walter’s earthcaretaker.com site (thank you Walter for publishing this!), I was astounded. You can find innumerable pictures on the web of birds happily posing on burdock. I’ve known common burdock my whole life as a live-and-let-live neighbor, hair-snarling issues aside. Now, I find out it is a mobster. How? The best I can figure out is that, since all the bird-killing reports I’ve read came from hikers, the bird trapping tends to happen in the wild where burdock gets loose and grows densely enough that the burs can ensnare the little guys. If any reader has better explanation, please let me know as I can add to this article.
After this article was written, the following was received from noted ornithologist, Todd Jason Underwood, who has studied the issue:
“Regarding your question about where entanglements occur, from my observations, they seem to occur where there are large concentrations of burdock plants. I have only found one or two birds (out of about 30) entangled where there are isolated plants. Entanglements also appear more common where birds are concentrated during migration as most entanglements occur during fall migration. Another important thing to note is that burdock entanglement occurs with other animals as well. Insects are commonly caught as well as bats. I even found a dead northern leopard frog hanging by its mouth from a burr.”