Thistles in Your Lawn? What to Know to Get Rid of These Prickly Weeds for Good

Thistles in the lawn are not unlike Lego bricks in a carpet—you often don’t notice these pesky lawn weeds with spiny foliage until you step on them barefoot and feel the pain they inflict. Because thistles grow close to the ground, they evade the sharp blades of lawn mowers. Not all thistles cause problems; it depends on the type and where they grow. Native thistles have high wildlife value while others are highly invasive species.

If you shy away from kicking off your sandals when walking across your lawn, it’s time to get rid of thistles. There are several ways to win the battle against them. Regardless of the method you choose, persistence is key. Here is how to get started on creating a thistle-free lawn.

Native vs. Invasive Thistles

There are several types of thistles growing across North America. Some of these spiny characters, such as the field thistle, are native nectar sources for hummingbirds, butterflies, and other pollinators. They are also a seed source for birds. Although native thistles rarely cause problems, they can be undesirable in garden beds and lawns where their prickly leaves could cause pain.

Non-native thistles are much more aggressive, invading pasture lands, open fields, and home lawns. Canada thistle is the most common thistle in home lawns. It produces a cluster of ground-hugging leaves with wavy, spiny margins. Step on a Canada thistle with bare feet and you’ll know it right away.

Canada thistles have a robust root system. Roots grow 6 feet or more deep and extend horizontally 15 feet or more. The vigorous roots form buds that develop shoots and tiny plants above ground. In a season or two, one Canada thistle plant can become a colony of hundreds of invasive plants thanks to a massive root network. This colony growth habit makes these thistles exceedingly tough to get rid of.

How to Remove Thistles in Lawn

Getting rid of thistles in your lawn or anywhere in your yard can be a challenge. Here's what to know about removing them by hand and with weed killers effectively.

Manual Removal

A chemical-free way of getting rid of thistles is to remove them by hand. In spring and early summer, when thistles are young, grab a thick pair of gardening gloves and get to work. Pulling thistles is easiest and most effective right after rain when the soil is moist so you can remove as much of the plant’s root system as possible. Remember, new thistles rise from the roots. Any bit of root left in the ground has the potential to produce a new plant.

Repeat hand-pulling thistles every week or two during the growing season. With vigilant work, you should see a reduced population of the spikey invaders the following year. Dispose of stems, leaves, and roots in the trash; they will quickly root if tossed in a compost pile. 

Chemical Controls

To control large patches of thistles in a lawn often requires herbicides. Apply an herbicide labeled for controlling Canada thistle in spring, early summer, or fall. The goal is to apply the chemical when the plant is actively growing so that it will take up the destructive compounds and succumb to the effects.

When applying any herbicide, follow label directions exactly. It’s important to not apply these chemicals too close to trees and landscape plants because it can harm them too.

Seasonal Tips for Preventing Thistles

Make your lawn unhospitable to thistles by creating an environment for vigorously growing turfgrass. Robust grass plants choke out thistles by shading the plant’s spiny foliage above ground and limiting rooting space underground. Practice these seasonal lawn care strategies for a lush, barefoot-ready carpet of turf.

Spring

Get in a mowing rhythm. A healthy lawn will grow fast in spring. Plan to mow every 4 to 6 days during optimal growing conditions. Regular rain and moderate temperatures are ideal for cool-season grasses. Moisture and high temperatures spur the rapid growth of warm-season grasses. Maintaining your grass at the optimal height for the species fosters dense growth that will push out thistles.

Be mindful of mowing height. The right mowing height for a lawn varies by the type of grass. Cut grass at its optimal height and form a thick mat of foliage with little space for thistles to invade. Cool-season grasses, such as Kentucky bluegrass and fescues, are generally maintained at 3 to 4 inches tall. Warm-season grasses, such as zoysiagrass and St. Augustinegrass, grow well when mowed at 1 to 2 inches tall.

Summer

Water smart. Water a lawn deeply and infrequently to promote strong growth. Aim to provide about 1 inch of water a week, supplementing with irrigation when natural rainfall isn’t adequate. Let the grass develop a deep root system by delivering all the needed water at once rather than splitting it over multiple applications.

Embrace dormancy. Summer heat and dry conditions slow down turfgrass growth; drought-tolerant grass turns dormant, a natural protective response to adverse conditions. Expect foliage to turn brown and dry temporarily. Although it might look dead, the turf is still alive and will start growing again as soon as regular rain returns.

Fall

Apply fertilizer. Autumn is the best time to fertilize a lawn. The moderate temperatures and more frequent rainfall encourage grass to grow and use available fertilizer efficiently to produce a deep root system late into fall. An extensive root system leads to dense, healthy growth take will choke out thistles. Choose an all-purpose lawn fertilizer and apply it according to label directions.

Keep mowing. Continue mowing the lawn until the grass stops growing in late fall. Grass that is too long going into winter is more susceptible to pests, diseases, and a thistle invasion. For vigorous growth the following spring, overwinter a lawn at the recommended height for the grass type.