Hardiness Zone: 6a
Samantha from Pittsburgh, PA
As you already know, Canada thistle is a really tough weed to eradicate. Unfortunately it competes well in deep, well-aerated soils-the same soils most flowers and vegetables prefer. The biggest challenge is the roots. They can colonize areas 3 to 6 feet in diameter. One of the best methods to get rid of Canada thistle is repeated pulling and mowing just when the flower buds are about to open. Pulling and mowing will eventually work to weaken the roots. When done over the course of three years, this method is said to kill up to 90% of the weeds. I actually like your black plastic idea. Dig up the soil well first, cover it with a good layer of compost and throw the plastic on things for the rest of this season. You'll substantially raise the fertility of your soil with the compost, which Canada thistle doesn't like. Next year you'll probably be home free. Maybe you can experiment with container gardening and try growing your veggies in containers for this one season. Burning in the late spring (May/June) can also work well, but must should also be done over the course of several years to be effective. Biological controls and herbicides are risky if your beds are earmarked for edibles.
I'm finding that the Canada Thistle has found its way through my black plastic. They are also all over the most shaded side of the house. The only way I know to get rid of them is to buy a hand weed puller and just make a day of it on a regular basis. That new "Weed Be Gone", kills it in about three days, too.
I live in Canada and don`t know what Canada Thistle is. What does it look like? Can you describe it for me? Maybe I`ve seen it and know of it by a different name. Thanks.
Never had Canada Thistle, but if you're planning on killing it off with black plastic, you can build a garden bed on top of that (or newspaper). Put newspaper (wet pads of it) over the ground and build up layers of earth, compost, grass clippings, dead leaves, etc. 18-24" high and plant in that. More on this subject in the book Lasagna Gardening. (I'm a container gardener but thought this was a terrific idea.)
Cantate, zone 8-9
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