By Gary Deters
One of the most common questions we receive from homeowners is how to manage or remove creeping Charlie (ground ivy) from their lawns. It’s an incredibly difficult weed to remove, especially when a homeowner prefers not to use herbicides.
I have a friend who inherited a backyard with a significant creeping Charlie and common violet infestation (Figure 1). My friend wanted to start over, try to lower the weed threshold, and plant a fine fescue to match the fine fescue in the front of the house. The yard was mostly shaded by trees and a garage, and he didn’t have an underground irrigation system. Because he didn’t want to use herbicides and the yard was a manageable size - 30 x 40 ft. (1,200 square feet), we decided to try an experiment. He had an opaque tarp we could lay down to block out the light, hoping to smother the weeds over a long period.
We put the tarp down on July 7 (Figure 2) with the initial plan of removing it in mid-August to seed. When we pulled it back in August, the creeping Charlie was mostly gone, but there were still plenty of green leaves on the common violets. Realizing they were tougher than we thought, we decided to leave the tarp down and transition to a dormant seeding strategy. This was all fantastic firsthand data for me, as I hadn’t run this exact experiment before. I really dislike giving out advice unless I have a clear picture of the potential successes and failures.
We finally pulled the cover in early November (Figure 3). While the creeping Charlie was completely gone, the common violet still seemed to be alive. We went ahead and prepped the ground anyway, seeding a fine fescue mixture at a rate of five pounds per 1,000 square feet.
The next step was simply being patient through the winter.
When spring arrived, the seedlings began to germinate (Figure 4), but as the fine fescue slowly started to fill in, the common violet bounced back quickly. Hoping to speed up the fine fescue’s establishment, I applied a starter fertilizer at a rate of 0.5 lbs N/1,000 square feet (I'm sure it also speeds up weed development). About a month later, I applied another 0.5 lbs N/1,000 square feet and put down some more seed to patch up some sparse areas, which is a common practice with dormant seeding. Because fine fescues are slow to establish, creeping Charlie also started creeping back in (Figure 5). This was likely due to years of creeping Charlie flowering and dropping seeds every year. Creeping Charlie produces seeds that can remain viable in the soil for years. There are also a number of other weeds that have moved into those open areas, including yellow woodsorrel (Oxalis), crabgrass, and broadleaf plantain.
Since this was primarily a learning experience and my friend was okay with the outcome, we aren’t going to start over. Instead, the plan is to keep the fine fescue as healthy and vigorous as possible to crowd out the weeds. However, given that this backyard is the absolute perfect environment for them, it’s likely going to be a shared space going forward. Even with the weeds, you can still see how nicely the fine fescue filled in (Figure 6).
Knowing what I know now, I would approach this project differently. Since the common violet managed to survive months under a tarp, I should have stuck to the mid-August seeding window. Seeding then would have provided a better environmental window for quicker establishment, giving the slow-growing fine fescue a better chance to outcompete the weeds, or at least hold them to a lower threshold. I also might have added some tall fescue and perennial ryegrass to the mix to act as a nurse crop to battle the weeds, trusting the fine fescue to outcompete the tall fescue and perennial ryegrass in the heavy shade long-term. Note that using a starter fertilizer with mesotrione (a pre-emergent) wasn't an option here, not only because of the no-herbicide rule, but because fine fescue is sensitive to mesotrione, and it could have injured the new seedlings.
For any homeowner thinking about using an opaque tarp to knock out creeping Charlie, it absolutely works for that specific weed. In this case, because the site was heavily shaded, I am not sure if the soil would have gotten hot enough for true solarization with a clear tarp.
Ultimately, every site has unique features, such as full sun versus shade, irrigation availability, how the space is used, foot traffic and many other reasons that will dictate your strategy and grass selection. The good news is that I learned a lot from testing this herbicide‑free tactic, and it may help guide future research.