This is the ninth in a series of blogs, shared with permission, about weeds in the garden. Each blog will discuss a common and specific weed found in Maine, its history, uses, what story it tells about the soil it grows in, and how to get rid of it. The original blogs, along with other gardening related blogs, can be found here.
This ugly little plant is what is actually responsible for your allergies – not that beautiful yellow flowered goldenrod you often attribute it to. Other names for ragweed include ambrosia, horseweed, asthma plant, bursages and burrobrushes, American wormwood, bitterweed, blackweed, carrot weed, hay fever weed, Roman wormwood, short ragweed, stammerwort, stickweed, tassel weed.
Common ragweed (Ambrosia artemisiifolia) is an annual that can produce 60,000 seeds a plant, and ragweed pollen is responsible for about half of all pollen related allergies in the US. It is also the first plant in my list that is actually native to North America! Common ragweed is considered an invasive, and in Queensland it is prohibited to be given away, sold or released without permission.
Although most of us want nothing to do with the plant, ragweed may have its uses. In the past it has been used to relieve nausea, fever, as a laxative, to soothe skin rashes and even as an antiseptic. There is a whole body of homeopathic research on the “like treats like” principle – where ragweed pollen is used to reduce allergy symptoms. The seeds, which are edible, pack an impressive amount of crude protein and fat, and each plant produces as much oil as a soybean plant. It is also a bioaccumulator for lead, which makes it useful in soil remediation.
What does it mean?
In general, ragweed prefers full sun, with disturbed and poorly aerated soil, with few competitors, is tolerant of dry soil and likes places where there is not much available potassium for existing plants. Pfeiffer supposes that a lack of copper in the soil might be part of why it creates such an allergy problem with its pollen.
One effective method of control is to slash or mow the plants, or to pull them, before they set seed but when they are fully mature. A variety of herbicides have been effective in killing ragweed, however in the United States, ragweed is becoming glyphosate resistant. Another method of control is the use of insects, two of which: stem-galling moth and the ragweed leaf beetle might help reduce the prevalence the weed. Finally, overcrowding is considered very effective as a method of eliminating ragweed in a couple of growing seasons.
Want to learn more?
If you would like to learn more about weeds, why they grow, and what that means about your garden, consider the following texts:
Weeds and Why they Grow, by Jay L. McCaman
Weeds and What They Tell Us, by Ehrenfried E. Pfeiffer
To make the fermented tea, you use a five-gallon bucket. Cut plant leaves into the bucket and loosely pack them in. Then, pour a kettle of boiling water over the leaves to get things started, and add unchlorinated water to fill it to the top. I used water from our rain barrels. Then “let sit for seven to ten days somewhere outside, loosely covered to prevent significant evaporation. This fermentation period makes the constituents that much more bioavailable for foliar absorption.” It gets pretty smelly with sulfur compounds–that’s how it is supposed to smell. You strain it when you use it. Once brewed, you dilute it, using about a cup of the tea per gallon of spray.
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