

Controlling unwanted plants in a prairie the old-fashioned way, by digging.
Manual Weed Control in a Prairie
January 12, 2006 by Evelyn J. Hadden

	frosty bull thistle
Digging easily controls the lovely bull thistle, a large clump-former that shades out prairie seedlings.

Weeds that appear in my prairie have mostly blown in, since clay subsoil doesn't hold a lot of weed seeds.

I tried not to be discouraged by the number of weeds during the first couple of years, because I read that prairie communities take years to establish. I aimed to just tackle the weeds as I could and not expect to get rid of all of them. In fact, I think it's likely that the increased diversity could benefit the prairie's health if a few individuals of different weed species stay, as long as they don't become dominant.

So I mainly focused on getting rid of the larger individuals that would produce seed, or even just taking off their seed stalks, and on pulling up hordes of tiny weed seedlings that covered an area and made it hard for prairie seedlings to germinate or grow.

My strategy has been to target certain weed species each year. The first year, I hand-pulled the prolific seeders that produced lots of seed and lots of close-together seedlings. These included curly dock (Rumex crispus), ragweed (Ambrosia artemisiifolia), pigweed (Amaranthus retroflexus), white mustard (Sinapis alba), and white and yellow sweet clover (Melilotus sp.). I left all the other clovers for their nitrogen-fixing abilities and for early insect nectar and early green groundcover.

Twice during the first year, I went out and pulled the above plants for several hours at a time, once early in the season and then later, trying to catch them young and trying not to disturb the seedlings of nearby prairie species.

That one year of pulling mostly eradicated all those species, and the next year I turned to dandelion (Taraxacum officinale), burdock (Arctium minus), plantain (Plantago major), and bull thistle (Circium vulgare), all of which needed to be carefully dug out to keep the surrounding seedlings intact, and all of which spread large leaves across the surface to shade out competing plants. I spent 6-8 hours per day for two days pulling the above weeds in June. So that was another few days' work early and later in the season.

(Note that bull thistle is clump-forming, unlike the creeping Canada thistle, but it does prolifically self-seed, and the dense foliage kills off other non-mature plants in a two-foot circle. I added bull thistle to my list of unacceptable species only because the prairie is fairly small and the thistles emit chemicals from their roots which discourage the growth of grasses.) All of the above large-leaved species are allowed on other parts of my property, where they perform useful services such as barring grass intrusion into woodlands and moving nutrients from the subsoil into the topsoil. I suspect that, as the prairie fills in, the lack of bare ground will severely limit the spread of these species, and I may then let scattered individuals stay.

I also leave self-sown mullein (Verbascum thapsis) in the prairie even though it produces clusters of large leaves that shade out surrounding seedlings. Mullein only likes the driest and best-drained south slope of the berm, which is a small portion of its total area, so I don't worry about it spreading across the prairie. Also I've seen woodpeckers feeding on my mullein stalks, though I don't know whether they were eating the mullein seeds or the insects that live on the stalks, so I keep the mullein to attract the woodpeckers. Finally, I find mulleins extremely striking in form with their single, thick, vertical stalks, and I love their large fuzzy leaves, so since they pose no threat to the prairie community, I'm happy for their contribution to its beauty.

The third year, I dug up reed canary grass (Phalaris arundinacea), which covers the surrounding wet meadows in a near monoculture. By the time I got around to weeding it, each self-sown plant had spread into a significant clump of foliage with stalks four feet high and roots one to two feet deep. The clumps were large and heavy (due to the dense roots and the clay soil), and when dug, they left gaping holes. I filled the holes with sand or gravel or mulch, whatever was at hand, then scattered seeds of nearby prairie plants over them.

Every year I pull up the running shoots of Canada thistle (Circium arvense), but after three years, I'm still not sure if this will eventually exhaust their roots or if they can stay ahead of me. I am hoping that a combination of strategies will drive them off -- my attacks will cut down on their available leaves and hence on their energy production, and the surrounding prairie plants will grow stronger and take away excess soil moisture, which seems to be one prerequisite for the thistles' growth. (I find them only in places that are reliably moist, not on dry or well-drained ones.)

However, it might be that they can continue to get enough soil moisture in the clay of the berm. I am working on finding some greedy prairie plants that will out-compete the thistles. Promising species include the silphiums and the perennial sunflowers (Helianthus sp., particularly H. maximilliani). I can't look to grasses, because the thistles release chemicals from their roots that inhibit the growth of nearby grasses, so I will have to look to forbs or possibly shrubs such as buffaloberry (Shepherdia canadensis), which I've planted in occasional clusters.

As the title of this article implies, I don't use herbicides to control weeds. I favor landscape management strategies (such as composting, mulching, and so forth) that have multiple benefits and no negative consequences.

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Species I've targeted for removal from my prairie were chosen because of personal experience with their opportunistic growth habits or because of warnings from respected prairie growers.

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