How to Control Canada Thistle

Canada thistle (Cirsium arvense) is a perennial broadleaf weed that can be especially troublesome in our lawns here in Michigan. This weed spreads quickly through wind blown seeds and a hearty creeping root system. The root system is especially difficult to control as it can grow new plants from any damaged area on the root. Due to this growth habit, it makes it so the plant can create dense patches of roots with multiple shoots, creating a challenge to control it. A major difficulty in controlling Canada Thistle is that it’s root system can be several feet deep and spread horizontally, well beyond the visible plants.

Having concerns over Canada Thistle being in our lawns isn’t just from an aesthetic standpoint. Canada Thistle can take over a lawn due to it competing with our desirable turfgrass and often winning the competition for nutrients and water resources. These plants, after they emerge in spring can continue to grow new shoots if water is available and then can produce seed once the flowering begins and the wind spreads the seeds. The seed spread and the strength of the underground root system is what makes any infestation of this plant persistent and very difficult to control. That is why early identification and treatment is an important step to keep it from taking over the desirable turf areas in our landscape.

Canada thistle leaves. | Leslie J. Mehrhoff, Univ. of Connecticut, Bugwood.org

How to tell if you have Canada Thistle growing in your lawn

In spring it starts off as a low growing rosette with deep lobed leaves and sharp spines in the leaf margins. The leaves themselves are smooth and slightly hairy. In late spring through summer, it will form a small flower head that may be pink, purple or even sometimes white. Canada Thistle is often found in colonies due to the underground roots producing new plants from buds on the root system or in damaged areas of the root system. Canada Thistle is easy to identify but it does have a look-alike in the Bull Thistle.

What can be done to prevent Canada Thistle in your lawn

Good lawn care is the best way to preventing Canada Thistle from gaining a foothold in your lawn. Keep your lawns thick and healthy with regular and proper watering, mowing and fertilization. This will lessen the open areas or thin areas of turf where Canada Thistle can establish itself. If you have any thin or sparse areas in your lawn, overseeding these areas will help the turfgrass fill in those areas and make it less hospitable to the Canada Thistle seeds if they should land there from the wind. Common areas that can be bare and need to be filled in are those lawn areas along walkway and driveway edges, fences and any areas in your lawn that may not be mowed as often as the rest of the lawn. Preventing Canada Thistle from developing flowers and seeds is also essential for effective control in the lawn.

What to do if Canada Thistle is in your lawn

Mowing before the plant develops flowers is only going to block flower growth, and only for the moment. Just mowing is not an effective control strategy for established patches of Canada Thistle. Digging out a single plant may not work completely to ensure that it will not resprout later because the roots that are left behind can resprout new plants. Using a selective broadleaf herbicide labeled for turf and for Canada Thistle or similar perennial broadleaf weed control can be effective but, proper application timing and application amount can be challenging for homeowners.

Optimal timing for control measures for Canada Thistle is in late summer or early fall when the plant is building its root system up for winter. A systemic herbicide applied during this time and stage of growth is more likely to have a greater control of the plant, as it will absorb the herbicide into its root system as part of this winter preparation process. When applying weed control measures during this time, it will have a better chance of success in controlling the plant and preventing the growth of new plants in the spring. Canada Thistle regrows from underground buds on the existing root system, thus having the herbicide in the root system will help to stunt or even prevent regrowth in the next growing season.

What we can do for you

Canada Thistle is a persistent turf weed because of its aggressive root system and its ability to spread to other areas of the landscape by seed disbursed by the wind. Successful control consists of early identification, proper lawn maintenance and timely control measures to reduce existing infestations. Owen Tree and Lawn Care can come out and positively identify if you have Canada Thistle in your lawn and develop a treatment and fertilization plan for your lawn to control the Canada Thistle and other common undesirable turf weeds so you can have a healthy and thriving lawn.

For more information or pricing information send us a message or give us a call today at 800-724-6680.