Jennifer Schultz Nelson
Extension Educator, Horticulture
Creeping Charlie holds a special place in my heart, as it is one of the first plants besides a dandelion that I learned was a "weed". For my dad, I think this plant is more than a weed, it is instead an evil enemy he has waged war with for more than my 36 years on earth.
For as long as I can remember, my dad has fought a relentless battle against this green enemy. I spent many an hour as a young girl charged with the task of pulling every bit of this plant that I could get my hands on, trying to beat back the tireless march of green across our yard.
As with many of our most hated weeds, creeping Charlie was actually brought here on purpose, with nothing but the best of intentions. European settlers are believed responsible for spreading creeping Charlie, more formally known as Glechoma hederacea, to all continents of the world.
Creeping Charlie is native to Europe and Southwest Asia. For thousands of years, Creeping Charlie was used in traditional medicines, and used as a food crop. As a medicine, it was used to treat everything from indigestion, to congestion, kidney disease, and as an anti-inflammatory agent. As a food, it was sometimes steeped as a tea rich in Vitamin C, as a cooked green, or as a salad green. It was commonly used to flavor beer before the advent of using hops. Despite its history, modern chemistry has isolated several compounds within creeping Charlie that are toxic to the liver, gastrointestinal tract and kidneys. So dishing up a big bowl of it to your family and friends is not a great idea.
The long history of using creeping Charlie in medicinal and culinary applications is the main reason European settlers brought it with them when settling around the world. They also appreciated the plant as an ornamental ground cover and potted plant. If you can set your dislike of the plant aside for a moment, it really does have attractive fan shaped leaves with toothed edges and pretty blue-violet flowers in the spring.
Close inspection of a creeping Charlie plant reveals an aspect of its pedigree that contributes to its aggressive nature in the garden. It has square stems, making it a member of the mint family. Anyone that has tried to keep mint contained in the garden knows its aggressive stems find a way over, under or through just about any obstacle in its path.
Combine this aggressive nature with the creeping Charlie's preferred environment of heavy, rich soil with high fertility and moisture, and you have a recipe for disaster. It also grows exceedingly well in shady locations where grass grows poorly. Guess where my dad has the most problem with creeping Charlie? You guessed it—on the edge of the vegetable garden which has some of the richest soil I have ever seen, and in a corner of the yard that is shady and moist where grass doesn't grow well.
Controlling creeping Charlie has been my dad's mission for years. This plant has just about every trait you wish a weed didn't have. You can pull it, but any little bit left behind will just grow into a new plant. Various weed killers may or may not be effective; different sources have recorded creeping Charlie's susceptibility and resistance to the same chemicals. Some years ago I knew a student whose Ph.D. project was finding a way to control creeping Charlie using herbicides. He told me a big part of the problem was in how creeping Charlie did not allow most herbicides to be distributed throughout the plant, resulting in partial dieback, but never complete elimination of the plant.
The best recommendations for chemical control I have seen recommend using products which are a combination of chemicals rather than a single one. One suggested combination I'm aware of is 2,4-D, dicamba, and MCPP. The idea is that by attacking the plant via different modes of action with different chemicals, this lessens the chances of a plant developing resistance to the chemicals. The chance of a plant having resistance to one chemical is a lot greater than a particular plant having resistance to three different chemicals that attack in three different ways.
One control method that someone asks me about each year without fail is using borax to control creeping Charlie. Like most home remedies, there is a grain of truth within this remedy, but I don't recommend people try it. Creeping Charlie is a plant that prefers soil with a low boron level; too much boron present will kill it. Borax contains boron, so the idea is to apply a solution of borax to the soil, thereby raising the level of boron in the soil to a point that the creeping Charlie dies. Seems simple, right? Well, the part that none of the home remedies out there mention is that there is a fine line between enough boron to kill creeping Charlie and enough boron to kill everything else around it as well. Plus, boron doesn't break down or otherwise "disappear" from the soil. So you create a long-term problem for yourself if you mess up a large part of your yard with an overzealous application of this home remedy. More is definitely not better in this case.
Two other control methods to consider are using a dethatching rake or if you're really desperate, killing off an area and starting over. After many years and probably hundreds of dollars in herbicides, a dethatching rake and an entire summer is what it took to finally rid my dad's yard of creeping Charlie. As he removed the creeping Charlie, he re-established new grass seed in the area to try and keep the creeping Charlie from moving back in. It worked in some spots very well, in others it is still closely monitored.
Some people wave the white flag and use non-selective herbicides like glyphosate (Roundup) or black plastic to kill off areas overrun with creeping Charlie. Placing black plastic over an infested area will heat up the soil and kill all plants and seeds present, but it may take a few days.
Most references I have seen say that herbicides work best on creeping Charlie in the fall. While that may be true, I speak from experience in saying it is the absolute worst time to try and pull it! After the plant flowers in the spring, the roots just seem to hunker down and settle in for the long haul. Pulling this weed while it is flowering is relatively easy. The plant is spending its energy on flowers in the spring rather than roots.
Honestly, in some cases, I think I would consider leaving the creeping Charlie alone rather than fight it, especially when it is growing where grass cannot. I guess I'm just not as much of a fighter as my dad is.