The Worst Weeds In Each State

You’ve likely dealt with weeds if you have a residential garden or lawn. Weeds aren’t always ugly, but they can seriously threaten your landscape. Try as you might, these problematic plants reproduce rapidly even in the poorest conditions, making any weed control efforts seem pointless. Luckily, knowing what kinds of weeds you’re dealing with is a great step toward eradicating problem plants from your landscape.

Types of Weeds

The Weed Society of America defines weeds as plants that cause ecological damage, economic loss, or public health problems. In a broad sense, they wreak havoc by growing where they aren’t wanted.

You may know weeds as the troublesome plants that steal resources from your precious garden flowers and turfgrass. Weeds are a problem because they don’t stop at residential gardens; they also steal resources from agricultural operations and wildlife. Some varieties are labeled as either noxious or invasive based on their abilities to cause more widescale harm.

• Noxious weeds are those identified by local or federal governments as threatening to public health, property, wildlife, or agriculture. They’re often called pernicious and persistent for their tendency to inhibit the growth of native and beneficial plants.
• Invasive weed species are those present in a non-native environment. These weeds are often introduced accidentally to an ecosystem and, thus, have no natural enemies to keep them in check. As a result, invasive species can spread rapidly and disrupt established ecosystems.

Not all invasive species are noxious, but most noxious species are invasive. Invasive plants are those that are introduced to a place in which they didn’t evolve. Much of the United States’ diverse flora wouldn’t exist without invasive species. However, noxious plants often fall into the invasive category for their ability to spread into a non-native area and cause damage.

Weeds To Look Out for in Your State

Weeds are adaptable and pernicious, which allows them to grow in various climates. For this reason, most weed species grow in many parts of North America. Now that you know why weeds are so troublesome, let’s look at some of the most common culprits across the U.S.

Check the U.S. Department of Agriculture’s noxious weed list for a more extensive look at weeds in your state.

More on North America’s Common Weeds

The following sections dive deeper into some of North America’s worst weeds. We’ll discuss noxious plants across the country to help you understand what’s potentially popping up in your landscape.

Bindweed

Bindweed (Convolvulus arvensis) is a perennial plant found throughout most of the U.S., minus the southernmost parts of states like Arizona, Texas, and New Mexico. The plant’s twisting vines and trumpet-shaped flower heads smother other plants by climbing their stems and preventing growth. Bindweed’s taproots form far-reaching underground rhizomes that can easily break off and form new plants with little to no resistance.

Canada Thistle

Canada thistle (Cirsium arvense) is a non-native plant that arrived in the United States in the early 1600s. Canada thistle is highly adaptable to many climates, making it invasive throughout most of the U.S. It’s considered noxious for its ability to decrease agricultural yield, displace native plants, and damage habitats for important pollinators. This pernicious plant forms sprawling root systems that constantly produce new shoots, enabling it to beat other existing vegetation.

Common Tansy

Common tansy (Tanacetum vulgare) is a perennial plant known to densely carpet roadsides and pastures. This plant has unique flowers that look like small yellow buttons. Tansy is considered a noxious weed for a couple of reasons. One, it’s quite pernicious and often out-competes native plant species. Two, it emits an oil that’s poisonous to humans and animals. If you remove tansy with the hand pulling method, wear thick work gloves to prevent skin rashes or irritation.

Ground Ivy

Ground ivy (Glechoma hederacea), also known as “Creeping Charlie,” is a groundcover plant found across North America. It germinates best in nutrient-rich, heavy soils like those of the Northeastern U.S. This weed is especially hard to control because it has brittle roots and stolons that easily break off and form new plants. It also reproduces quickly and densely, often crowding out established native plants. Ground ivy is poisonous to grazing animals like goats and horses when eaten in large quantities.

Knapweeds

Spotted knapweed (Centaurea stoebe), diffuse knapweed (Centaurea diffusa), and Russian knapweed (Rhaponticum repens) are noxious weed cultivars commonly found in sandy soils along roadways, fields, and gravel areas.

Spotted and diffuse knapweeds are biennial weeds with few natural enemies, allowing them to proliferate in farmland areas and ruin crops. Their prominence in pastures lends heavily to spreading through hay bails and feed products. They also have deep-reaching taproots that prevent easy removal.

On the other hand, Russian knapweed is a perennial weed with dense, spreading root systems. This knapweed variety is the most harmful because it’s adapted to poor soil conditions, allowing it to spread almost anywhere. Russian knapweed is distinguishable from other species by its rounded, transparent seed heads.

Kudzu

Kudzu (Pueraria montana), also known as the “mile-a-minute weed,” is a fast-spreading invasive plant found most commonly in the Southeastern United States. This persistent plant gets its nickname from its ability to grow up to a foot per day in different directions, quickly overtaking abandoned homes, tree groves, and garden fences.

Though farmers originally used the plant as an erosion control tool, conservation specialists quickly discovered its overly competitive nature. Kudzu grows through stolons, rhizomes, and nodes, allowing it to invade surrounding landscapes with creeping green leaves.

Leafy Spurge

Leafy spurge (Euphorbia esula) is a noxious weed known to crowd pastures, roadsides, and prairies. The plant grows well in various sun and soil conditions, making it a prevalent problem in most of the United States, but mainly in the northern region.

Leafy spurge spreads via extensive root systems that expand underground, smothering out other plants. It’s so notorious that it can ruin entire crop yields. Hayfields infested with leafy spurge are prohibited from moving through the production line. Such weed control efforts are necessary but also result in great crop and economic loss.

Purple Loosestrife

Purple Loosestrife (Lythrum salicaria) is a perennial plant often found in North American wetland regions. This spiky purple flower once resided in home gardens and landscape designs; however, it soon earned a spot on the noxious weed list for its tendency to spread uncontrollably and negatively impact native plants. Purple loosestrife can produce over 2.5 million seeds each year, which fall from the parent plant and germinate the following season.

Toadflax

Dalmatian toadflax (Linaria dalmatica) and yellow toadflax (Linaria vulgaris) were originally brought to North America as ornamental plants. They’ve since moved onto the noxious weed list for their tendency to disrupt native ecosystems. With clusters of snapdragon-like flower heads, toadflax may look pretty, but its spreading habit poses a serious threat to other plants. With a deep, extensive root system continuously producing off-shooting plants, toadflax can out-compete annuals and shallow-rooted perennials for vital nutrients and moisture.

Both toadflax cultivars contain oil compounds that are toxic to cattle. While animals typically steer clear of toadflax, the plant still crowds out valuable foraging plants for wild fauna.

Yellow Starthistle

Yellow starthistle (Centaurea solstitialis) is a flowering plant known to infest roadsides, pastures, wastelands, and hayfields. The plant’s common name comes from its bright yellow, thistly blossoms, and spiny base.

Yellow starthistle forms extensive underground infestations that rapidly deplete soil quality, starving nearby plants of nutrients. The plant is highly toxic to horses, causing a severe and fatal disease once ingested. Horses are currently the only known animal with a severe reaction to starthistle, but the plant still harms other animals by reducing their food sources.

Garlic Mustard

Garlic mustard (Alliaria petiolata) is an herbaceous winter annual that sprouts long, self-pollinating seedpods. Without pollination needs, this plant rapidly spreads throughout riverbanks, forested areas, and pastures, overcrowding native plants as it goes.

Garlic mustard colonies typically pop up in the early spring in small mounds of leaves. After maturing through the growing season, this problematic plant sprouts flowering stems and seed pods that kick-start rapid, uncontrollable spreading. Even if the plant is damaged, the broken stems will form seeds that produce new plants.

Final Thoughts

Now that you know the common weeds in your area, you can learn how to effectively control and eradicate them. Weed control isn’t easy; it may take getting down and dirty to solve the problem completely. However, your efforts will undoubtedly be worth it when your lawn and garden can flourish to their full potential.

Our garden and lawn care experts have you covered if you don’t know where to start for weed control. For DIY solutions, read our guide to natural weed killing for more information on using physical barriers and hand pulling to rid your garden of invasive plants.