Sunday, May 20, 2007

Thistle control in our prairie

Planting wildflower meadows - natural landscaping with prairie wildflowers and grasses that are native to North America - is billed as a low-maintenance, earth-friendly way of gardening that doesn't need much in the way of fertilizers, herbicides, pesticides or watering.

This sounded good to us, so in 2000, we planted a short-grass prairie meadow, shown here four years later. The planting includes perennials - forbes in prairie gardening lingo - and short grasses. Actually, as it covers more than two acres, we didn't plant it ourselves, but hired Wildflower Farm to sow it with a tractor and seed drill.

Our neighbors were skeptical: sure, a city couple moves to the country, wants wildflowers - it's never gonna work. However, I had researched the idea carefully, and found that, besides money for the seeds and planting (it's not cheap!), it takes patience because the real show of flowers from seed takes three years to get blooming.

Wildflower Farm's method included planting a nurse crop of annual rye grass to deter weeds without choking out the emerging native grasses and wildflowers. Doing it this way made a lot of sense to me.

Our meadow is seven years old and quite established now, and it really is a joy and my favorite part of the property. It's an amazing haven for birds all season long, and attracts countless butterflies in late summer.

The classic way of managing a prairie is to burn it in early spring every few seasons to keep weeds and woody plant interlopers in check. We have done a controlled burn twice, and now schedule one every five years or so. Fire regulations - plus plain old safety concerns - don't allow a do-it-yourself burn, so we have to hire pros for the job. This is hugely expensive: the insurance alone costs almost $1,000.

The prairie meadow has done beautifully. However, there have been challenges. After four years we had a severe infestation of Canada thistle, the nasty one that spreads via root growth like a ground cover. (Why it's called Canada thistle is beyond me: the plant is a native of Eurasia, and shouldn't be blamed on poor defenceless Canada.)

When the thistles got really bad, I consulted one of my favorite reference books, Gardening with Prairie Plants and read that "Canada thistle (Cirsium arvense), native of southeastern Eurasia, is eventually outcompeted by big bluestem in northern tall grass prairies but ruins short grass prairies."

I didn't want this to happen, so we bit the bullet and began to remove the thistles by cutting them down while they were in flower in mid-summer. The idea was to get them out before they could go to seed. It was a nasty, hot prickly job, relieved only by the lovely scent of the plants. (Who knew that thistles have a lovely fragrance?) We took the thistles away with our front-end loader tractor. Eighteen loads (!) later we were done: the job took three or four of us several days working in plants that were waist-high.

The following spring, we decided to use herbicide - 2,4-D (Killex, the stuff used on lawn weeds) - on the thistles as they emerged early in the season. Obviously, I prefer to avoid herbicides, but we couldn't dig the thistles out as the area was way too big for hand removal of a plant that spreads by root runners.

To avoid getting the herbicide on other plants, we used a sponge applicator, the Weedeezy weeding stickthat you put on top of the plant and press down and twist. Each weeding stick holds about a litre of water into which you mix the corresponding amount of herbicide concentrate.

To do the job, my husband and I walk five-foot wide swaths of the meadow hitting each thistle as we see it. We do this in early May just as the thistles start to grow. The first season, we repeated the application three times. Subsequently, we've only had to do it twice, about a week to 10 days apart.

The thistles are no longer over-running the meadow. We'll never eradicate them entirely, but then again our meadow will not be ruined as long as we keep this up. The price is one or two mornings spent applying spot herbicide each season. We put on the smallest amount possible, but this makes all the difference.

This experience - our success controlling a very nasty weed - is one of the reasons that I don't support blanket bans on herbicides. There are legitimate reasons to use them. It's a trade-off: a small amount of herbicide for weed control, with virtually no harm to the environment.

In our situation, allowing the thistles to proliferate would have spoiled the landscape feature that is the biggest draw to wildlife we have on our property. Perhaps an ecological purist would not have used herbicide, but the price would have been high: the ruin of a short grass prairie. I think we made the right decision.