How To Control Smartweed, A Weed That Thrives In Wet Environments

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How To Control Smartweed, A Weed That Thrives In Wet Environments

How To Control Smartweed, A Weed That Thrives In Wet Environments

Ruud Morijn Photographer/Shutterstock

Smartweed, or officially Polygonum, has an incredibly misleading name. This weed loves a wet climate, and you’ll find it especially loves growing around ponds and creeks. It also grows along roads, ditches, and beside railroad tracks. It is not smart, but it is tenacious and prolific. So prolific, in fact, that if you have them in your landscape, you might be looking for a way to control them. This, of course, is where we come in!

Smartweed is considered a wildflower as well, and it’s fairly easy to identify. The leaves are hairy, lancet-shaped, and may have purple blotches on them. The stems have “knees,” or swollen areas covered in pale green sheaths that separate its segments. And the flowered tops are long cones at the ends of the stalks in pink to a bright reddish-purple color. They produce a huge amount of seeds, with each plant producing up to 20,000 of them! As you can imagine, this can get out of hand quite quickly if you’re not careful.

How to smartly control smartweed

Man using a flame weeder

Gabor Tinz/Shutterstock

Luckily, smartweeds have shallow taproots, so pulling them out may be your best bet. However, like most weeds, you must be sure you get every little bit, or they’ll return. The main thing to remember is to never let them seed. If you find them in your lawn, simply mow them down. Just make sure to put the debris into bags and toss them out so seed heads don’t have a chance to accidentally sow themselves. If you don’t have a problem with using chemicals, several weed killers should work too.

The problem with using herbicides or chemicals is that they can harm plants you aren’t intending to kill. Plus, we’re learning more all the time about how harmful they are to our climate and ecosystem. The best way to control smartweed is actually by torch! That’s right, because only one-tenth of a second of heat from a gas torch not only kills it but also ensures that it won’t return! These are called flame weeders, and they’re basically a wand connected to a propane tank. It’s the best way to take care of many persistent weeds, especially annuals like smartweed.

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Dr Heidi Parkes

By Dr Heidi Parkes

Senior Information Extension Officer QLD Dept of Agriculture & Fisheries.