How to Manage Thistle without Herbicides
We know, we know: you’re not supposed to hate. But it’s hard to find anything to like about Canada thistle. We can give it credit for being a pioneer species capable of recolonizing bare ground, but no one is thrilled to find it in their yards, especially if you like walking barefoot in your grass.
It can be tempting to reach for an herbicide after a thistle leaf stabs the sole of your foot for the umpteenth time, but it’s worth trying out some natural approaches to thistle control first. While some herbicides have proven marginally effective against thistle, they also decimate the microbial life in your soil, leaving your turf weak and susceptible to future weed invasions (not to mention wreaking havoc on birds and pollinators!). Thankfully, there are some natural ways to address thistle in your yard.
Before we get there, it’s important to understand how thistle propagates. Most of us have likely seen the large flower heads that Canada thistle produces. Those purple flowers distribute upwards of 5,000 seeds each, and those seeds can stay viable in the ground for 20 years before germinating. The other way that thistle propagates is less visible: its extensive root system. A mature thistle plant has roots that stretch six feet deep and send off multiple sideways-growing rhizomes that pop up as seemingly new plants, creating the dreaded “thistle patch”.
To manage thistle’s spread and control established plants, you need to prevent the flowers from going to seed and weaken the thistle’s root system. To prevent seeding, consistently deadhead the stalks by chopping them off with a weed-wacker. Be sure to knock down not only the thistle plants growing in the yard, but also the thistle growing in unmanaged areas immediately surrounding the yard. And keep at it! Buds can regenerate in just a few weeks, so keep an eye on them and weed-wack again before the flowers appear.
In addition to preventing the plant from going to seed, you can combat thistle by weaking its root system. The best way to do this is to repeatedly remove the top-growth by snipping off the leaves. This practice effectively starves the plant by limiting the flow of nutrients from its leaves to its roots. According to guidance from Cornell University, consistently removing shoots from the plant may eliminate the weed within two years.
Of course, there’s no offense like a good defense. Your first and main priority should be to grow a thick and healthy lawn that thistle can’t infiltrate in the first place. That means mowing tall, watering deeply and infrequently, and using a holistic soil fertility program. New here? Check out these other blog posts to learn how to cultivate a healthy, resilient yard:
1. Three Management Mistakes that are Killing your Lawn