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Confession – I have a goutweed problem. Like many gardeners, I wrestle annually with this invasive perennial, but I don’t think I’m winning. In fact, I probably didn’t take it quite as seriously as I should have when I first noticed it growing in a corner of the garden about four years ago. It took mere weeks for that tiny patch to double in size and it’s now conquered three areas of my yard. After watching its steady progression in my garden, I realized last summer, that I needed to get serious about getting rid of it.
Goutweed was originally introduced to North America as an easy care groundcover, thriving in shade, partial shade, and full sun. It will also grow in a range of soils, but spreads quickest in cultivated garden soil. In terms of survival skills, goutweed is the cockroach of the botanical world. It produces a web of underground rhizomes from which each leafstalk emerges. The leaves are comprised of three groups of three leaflets and can be green or variegated.
Green goutweed, the type that I (unfortunately) have is a beast to eradicate, yet is not considered a noxious weed in Canada. Certain states, like Massachusetts and Vermont, have added it to their ‘Prohibited Plant List’ and it can no longer sold or traded. Incredibly, there are still garden centres in my province that sell goutweed as a groundcover! The variegated type, often called Bishop’s Weed or Bishop’s Curse, is slightly less thuggish, but if allowed to go to seed, it can produce all-green, super-aggressive seedlings.
Three ways to deal with invasive weeds like goutweed:
- Cook ’em – Solarizing invasive weeds is among the most effective of the organic methods, but it requires time, heat, and the ability to put up with an ugly piece of plastic in your garden for several months. Begin by finding a sheet of black or clear plastic that is large enough to cover the patch, plus a few extra feet in every direction. Water the area well and cover with the plastic, burying the edges to lock in the heat and moisture. You can also use bricks to weigh down the plastic if burying isn’t possible. Under the plastic, the temperature can rise to 130 F (55 C), killing weed seeds, pests, disease pathogens, and hopefully, goutweed. Remove the plastic after 6 to 8 weeks and wait several weeks to see if the goutweed rhizomes survived and will re-sprout. If there are no signs of goutweed after a month, you might, just might mind you, be in the clear.
- Smother ’em – This is the first goutweed-busting method that I decided to try, with varying success. Begin by mowing or weed-whacking your goutweed into submission, cutting it as short as possible. Cover the area with cardboard, again being careful to expand several feet past the goutweed, and top with a thick layer of mulch – bark nuggets, shredded leaves, etc. Wait. Smothering can take a long time – up to two years. If using an organic mulch like shredded leaves, you can add some soil and plant directly in the materials after a year or two, but only IF NO GOUTWEED HAS EMERGED.
- Spray ’em – Now before you get your knickers in a twist, I’m talking about natural sprays made with citrus oil or vinegar, 20% horticultural vinegar to be exact. I have had modest success with this industrial strength vinegar, but it also takes time, perseverance and hot, dry weather. I’ve got the time and the perseverance, but the hot, dry weather can be tricky in Nova Scotia. Last summer I sprayed one of my goutweed patches with vinegar three times – mid-July, early August, and late August. The first dose did nothing. The second dose curled and browned the leaves within days of spraying. The third dose knocked it down, and up until a few days ago, I thought it was gone… but then I noticed the sprout in the above photo. That said, this was a dense 5 by 20 foot forest of goutweed last summer and I’m down to one sprout. I think it’s time to pick up more vinegar and tackle those other two patches.
Bonus advice – Move. This is the only known method for 100% elimination of goutweed.
Do you have goutweed? What have you found effective for controlling this obnoxious weed?