Three Ways to Get Even with Thistle
"I saw your article on How to Get Rid of Thistle & Bamboo at the Garden's Alive website. So now I know that I need to cut ALL of the plants at the base. You also suggested using a 20% acidity Grain based vinegar as a natural herbicide.
"I would love to replant a TREE in this area again; and the sooner the better as I miss the shade. I also have Thistle popping up in the front of the house. I dug around the thistle and cut it below the soil level, covered it with a piece of black plastic and covered the plastic with dirt. It returned in the same spot. It is a horrid weed. I have never seen anything like it. In the back of the house, where the tree was, and where the majority of the thistle is, I have lots of Hosta and other beautiful plants and I don't want them to die from the vinegar. Please help!"
A. There are many varieties of thistle; are you sure you have "Canadian" thistle (which is actually from Europe)? Control is pretty much the same for all thistles, but it's nice to know the actual name of the plant you're fighting so you can curse it properly.
Control method #1: Rope a Dope. Thistle spreads by underground roots as well as by seed. If you cut it down just as the flowers begin to color up, you will starve those roots of a lot of energy. Over the course of a few years, this will greatly weaken the underground part of the plant. But we need to be realistic here: thistle is not a 'one season' job. It's going to take time and determination. Get one of them ginormous outdoor umbrellas to give you shade in the meantime.
I found the following sage advice at one of the websites I visited for this piece: "timing of cutting is crucial. This should take place just before the flower bud turns purple, as this is when the maximum reserves from the thistle roots are being used to produce seed. The old saying often proves true: 'Cut a thistle in June, it's a month too soon; Cut a thistle in July it will surely die.'"
Tilling the area, of course, would be a huge mistake as it would spread the underground plant parts, but above ground mowing IS recommended. Follow the same schedule as above and then mow again at the end of the season.
2. Vinegar: I found a great Bulletin from the USDA's Agricultural Research Service that strongly supports the use of vinegar as a non-selective herbicide; AND the researchers specifically used Canadian thistle as one of their target plants.
I quote: "The [researchers] hand-sprayed the weeds with various solutions of vinegar, uniformly coating the leaves. The researchers found that 5- and 10-percent concentrations [of vinegar] killed the weeds during their first two weeks of life." (Supermarket vinegar has been diluted with water to five percent acidity; specialty "horticultural" vinegars are acidic in the eight to twenty percent range.) Note: Always use protective eyewear when spraying vinegar and use cardboard or other protective devices to keep it off wanted plants.
The Bulletin continues: "Older plants required higher concentrations of vinegar to kill them. At the higher concentrations, vinegar had an 85- to 100-percent kill rate at all growth stages". And get THIS: "Canada thistle, one of the most tenacious weeds in the world, proved the most susceptible [to vinegar]; the 5-percent concentration had a 100-percent kill rate of the perennial's top growth. The 20-percent concentration can do this in about 2 hours."
#3: Eat your enemies! The charming website Wild Harvest dot org covers this topic wonderfully. Again, I quote: "You can eat all parts of thistle - root, stem, leaves, flowers, seeds. My boys used to enjoy taking a tall thistle, and with their pen knives on a walk, would strip it down to just the stem (to remove the prickly leaves). You can then choose to peel the skin of the stem or eat it as is. My boys would chomp on this refreshing watery bitter bite until they learned they could take it home and dip it in sugar, akin to rhubarb stalks.
"Other ways you can use the stem are to chop it into inch long pieces and add to salads as a fresh watery, bitter crunch; or add the inch long pieces of stem to a stir fry, braising them in soy sauce and oil. Or how about dipping the sticks of stem into batter, then deep frying and dipping in a sauce? Some thistles can grow to five or six feet high...That's a lot of stem!"
The author, who delves into many other uses and recipes for this "weed" is a young woman (well, she sure LOOKS young even though she has three kids) named Diana Hammill Page (or "Di" to her friends). She lives and teaches on the other side of The Pond, specifically York in the UK. There's lots more thistleish to relish at the Wild Harvest website.