Johnsongrass, quackgrass, puncturevine, bull thistle, field bindweed, spotted knapweed, and purple loosestrife are among the common weeds in Arizona, and they can take over your lawn in no time.
Weeds compete with turf grass, depriving it of sunlight, water, and other nutrients. They create a perfect hiding spot for pests. In this article, we’ll describe the most common weeds in Arizona and how to get rid of them.
We also have an excellent guide to the Best Weed Killers for Arizona to help you eradicate weeds and keep them away.
Grassy weeds
Grassy weeds look similar to turfgrasses and share some of their characteristics, but they are undesirable and don’t produce the same quality lawn. If you suddenly notice rapid grass growth within your lawn or at its edges, there’s a good chance they are grassy weeds.
Check out our guide on controlling grassy weeds.
Johnsongrass (Sorghum halepense)
Johnsongrass is a common weed throughout the state. This warm-season perennial grows 2 to 7 feet tall and spreads aggressively by thick rhizomes. It grows densely and can quickly displace turfgrass and other vegetation.
This weed thrives in full sun but can adapt to various soil types. Apply pre-emergent herbicides in late spring to prevent johnsongrass from germinating. Johnsongrass is toxic to humans if eaten.
Learn more about Johnsongrass.
Weed type: Grass
Life cycle: Warm-season perennial
Sun: Full sun
Soil: Thrives in various soil conditions
Toxic: Toxic to humans if eaten
How to identify Johnsongrass: Narrow, smooth, bright green leaves with a vein in the center. The grass is 2 to 7 feet tall, and the stems are reddish near the base.
How to get rid of Johnsongrass: Pull the weeds by hand if the infestation is small. For larger infestations, mow repeatedly and use post-emergent herbicides with glyphosate. Then, overseed with a desirable grass type. Maintain a healthy and dense lawn to prevent the weeds from coming back.
Quackgrass (Elymus repens)
Quackgrass is a cool-season perennial that grows 1 to 3 feet tall. It can resemble desirable cool-season grasses, except it has long, flat leaves with a bluish-green tint. It’s common throughout Arizona and spreads through rhizomes, which helps it quickly outgrow turfgrasses.
This weed grows best in partial shade and thrives in loamy and sandy soils. However, it can withstand most soil types. Quackgrass is hard to eradicate once established, so apply pre-emergent herbicides in early fall to prevent it from germinating.
Learn more about quackgrass here.
Weed type: Grass
Life cycle: Cool-season perennial
Sun: Partial shade
Soil: Thrives in sandy and loamy soils; tolerates most soil types
Toxic: Non-toxic
How to identify quackgrass: Long, flat, bluish-green leaves that are coarse. It’s 1 to 3 feet tall.
How to get rid of quackgrass: Pull weeds by hand if the infestation is contained in one area. Apply post-emergent herbicides containing glyphosate for larger infestations. Then, mow and overseed your lawn. Maintain a dense lawn to prevent the weeds from returning.
Southern sandbur (Cenchrus echinatus)
Southern sandbur is a warm-season annual weed that grows up to 2 feet in height. Its stems are round with a reddish tint at the base, and the leaf blades are flat. The seedhead has sharp spines (burrs) that easily disperse by attaching to clothing or pets. Southern sandbur is a nuisance throughout Arizona, from Tucson to Phoenix.
This weed thrives in full sun and dry, sandy soils. Southern sandbur is non-toxic, but its burrs are sharp and can harm you and your pets. Apply pre-emergent herbicides in spring to prevent this weed from germinating.
Learn more about Southern sandbur.
Weed type: Grass
Life cycle: Warm-season annual
Sun: Full sun
Soil: Dry, sandy soil
Toxic: Non-toxic
How to identify southern sandbur: Flat, green leaves with round, reddish tint stem. The seedhead has sharp, spike-shaped flower clusters. It’s about 2 feet tall.
How to get rid of southern sandbur: Use post-emergent herbicides with glyphosate and then overseed with desirable grass type. Avoid pulling the weeds by hand because you can injure yourself.
Cheatgrass (Bromus tectorum)
Cheatgrass is winter- or spring-annual grass that grows up to 3 feet in height. Its stems are thin and flexible, and the leaf blades are covered with soft hairs. Cheatgrass germinates quickly and can deprive your turfgrass of water and other nutrients. This grass is common throughout the state, from Northern to Central to Southern Arizona.
Cheatgrass grows best in full sun and any well-drained soil. Apply pre-emergent herbicides in the fall and early spring to prevent this weed from germinating. Cheatgrass seeds can harm pets by damaging their lungs and abdomen if inhaled. Also, the seeds can cause extreme irritation to your pets when they attach to ears, nose, or toes.
Learn more about cheatgrass.
Weed type: Grass
Life cycle: Annual
Sun: Full sun
Soil: Well-drained soil
Toxic: Toxic to pets
How to identify cheatgrass: Leaf blades are green, flat, and 2 to 6 inches long. They are covered in short, soft hairs. The stems are thin and flexible. Cheatgrass ranges from 4 to 30 inches in height.
How to get rid of cheatgrass: Pull the weeds by hand if the infestation is contained in one area. If the infestation is severe, mow repeatedly and use post-emergent herbicides with glyphosate. Then, overseed with a turfgrass.
Broadleaf weeds
Broadleaf weeds have wider leaves than grass and often have clusters of flowers. They multiply rapidly and can be difficult to control once they start growing in your yard.
Check out our guide on controlling broadleaf weeds.
Puncturevine (Tribulus terrestris)
Puncturevine, also known as goathead, is a summer annual that grows in a mat-like form. The stems spread 3 to 4 feet radially. This weed produces fruits with long, sharp spines that can puncture feet and bicycle tires, which is how it gets its name. The fruits drop and spread easily by splitting into five hard burrs.
This summer annual thrives in full sun and sandy soil but can adapt to most soil types. Apply pre-emergent herbicides from late winter to mid-spring to prevent this weed from germinating. Puncturevine is toxic to pets.
Learn more about puncturevine.
Weed type: Broadleaf
Life cycle: Summer annual
Sun: Full sun, partial shade
Soil: Thrives in sandy soil; tolerates most soil types
Toxic: Toxic to pets
How to identify puncturevine: Mat-like growth with green leaves. The stems are round and hairy, and the fruits have long, sharp spines that resemble a goat’s head. It spreads 3 to 4 feet radially.
How to get rid of puncturevine: Uproot the plants with a hoe, being careful not to get injured by the sharp fruits. If the plants are young, use post-emergent herbicides with glyphosate.
Bull thistle (Cirsium vulgare)
Bull thistle is a biennial that germinates in the fall and spring and flowers from summer to early fall. This weed is 2 to 5 feet tall and is self- or insect-pollinated. It produces 10,000 seeds per plant each season, quickly displacing desirable grass and plants from your lawn. Bull thistle has purple flowers and green spines.
This broadleaf biennial thrives in full sun and moist clay, loamy, or sandy soils. Apply pre-emergent herbicides in early fall and spring to prevent seeds from germinating. Bull thistle is non-toxic but has spiky rosettes and thorny spines around the stem that pose a threat to you and your pets.
Learn more about bull thistle.
Weed type: Broadleaf
Life cycle: Biennial
Sun: Full sun
Soil: Moist clay, loamy, or sandy soil
Toxic: Non-toxic
How to identify bull thistle: Branches have green spines, and the leaves are hairy on the upper side and cottony below. Flowers are purple with sharp spines. It’s 2 to 5 feet tall.
How to get rid of bull thistle: Uproot the weeds with a hoe, being careful not to get injured by the sharp spines. Use post-emergent herbicides with glyphosate for larger infestations.
Field bindweed (Convolvulus arvensis)
Field bindweed looks beautiful with trumpet-shaped flowers like morning glories, but don’t let that deceive you. This perennial vine spreads by rhizomes and can quickly choke desirable grasses and plants by growing along the ground or up through structures. Field bindweed is common throughout Arizona, from Sedona to Scottsdale to Flagstaff.
This perennial thrives in full sun and moist clay, loamy, or sandy soils. It can also survive in soil with moderate moisture. Field bindweed is hard to eradicate once established because the roots can grow as deep as 30 feet. We recommend applying pre-emergent herbicides in early spring to prevent it from germinating. This vine is non-toxic.
Learn more about field bindweed.
Weed type: Broadleaf vine
Life cycle: Perennial
Sun: Full sun
Soil: Moist clay, loamy, or sandy soil; tolerates soil with moderate moisture
Toxic: Non-toxic
How to identify field bindweed: Heart-shaped leaves and trumpet-like whitish-pink flowers that resemble morning glories. Its stems are twining and 1 to 6 feet long.
How to get rid of field bindweed: Pull weeds by hand for smaller infestations. If the infestation is severe, mow repeatedly and apply post-emergent herbicides with glyphosate. Then, overseed with a turfgrass.
Spotted knapweed (Centaurea maculosa)
This perennial looks beautiful with vibrant lavender flowers, but don’t fall for it because spotted knapweed can quickly outgrow desirable native plants. The seeds are spread by the wind, which makes it highly invasive. This weed has grayish-green leaves and grows up to 5 feet in height.
Spotted knapweed thrives in full sun and dry, sandy soils. Apply pre-emergent herbicides during spring to prevent this weed from germinating. Spotted knapweed is non-toxic.
Learn more about spotted knapweed.
Weed type: Broadleaf
Life cycle: Short-lived perennial
Sun: Full sun
Soil: Dry, sandy soil
Toxic: Non-toxic
How to identify spotted knapweed: Grayish-green hairy leaves and vibrant lavender flowers. Bracts (the part at the base of the flower head) have triangular black spots. It ranges from 1 to 5 feet in height.
How to get rid of spotted knapweed: Pull weeds by hand or spot-treat them with post-emergent herbicides containing glyphosate for larger infestations. Then, mow and overseed your lawn.
Canada thistle (Cirsium arvense)
Canada thistle is a broadleaf perennial that spreads by rhizomes. It quickly outgrows desirable turfgrass and native plants. This weed is 2 to 5 feet tall and produces small violet flowers that grow in clusters. The leaves have wavy edges and are spiky like other thistles.
This perennial thrives in full sun but can also withstand partial shade. It prefers well-drained clay soil. We recommend using pre-emergent herbicides in spring to prevent Canada thistle from germinating. This broadleaf perennial is toxic, and the thorny spines around the stem can harm you and your pets.
Learn more about Canada thistle.
Weed type: Broadleaf
Life cycle: Perennial
Sun: Full sun
Soil: Well-drained clay soil
Toxic: Toxic to humans and pets
How to identify Canada thistle: Lance-shaped, spiky leaves with wavy edges. Teardrop-shaped purple and pink flowers appear in the summer. It’s 2 to 5 feet tall.
How to get rid of Canada thistle: Spot-treat the weeds with post-emergent herbicides containing dicamba or glyphosate. Mow repeatedly and overseed with a desirable grass type.
Purple loosestrife (Lythrum salicaria)
Purple loosestrife is a broadleaf perennial that spreads by rhizomes and seeds. The thick roots spread vigorously, depriving native plants of water and other nutrients. This weed is 6 to 10 feet tall, and showy purple-pink flowers appear during mid to late summer. The lance-shaped leaves are hairy and stemless.
This weed thrives in full sun and well-drained soils. Purple loosestrife is difficult to control once established, so apply pre-emergent herbicides in spring to prevent it from germinating. This broadleaf perennial is slightly toxic to humans and pets.
Learn more about purple loosestrife.
Weed type: Broadleaf
Life cycle: Perennial
Sun: Full sun
Soil: Well-drained soil
Toxic: Toxic to humans and pets
How to identify purple loosestrife: Lance-shaped, hairy leaves arranged in opposite or whorled patterns. Tall, narrow spikes of purple-pink flowers appear during mid to late summer. It’s 6 to 10 feet tall.
How to get rid of purple loosestrife: Uproot the weeds with a hoe if the infestation is contained in one area. For severe infestations, apply post-emergent herbicides with glyphosate. Mow repeatedly and then overseed with a desirable turfgrass to prevent regrowth.
Yellow star thistle (Centaurea solstitialis)
This winter annual spreads by seed and grows fast, developing roots that extend over 3 feet deep. Yellow star thistle depletes soil moisture, reducing the water available for desirable grasses and plants. It produces bright yellow flowers with sharp spines at the base from summer to mid-fall. This weed is 1 to 3 feet tall and is common throughout Arizona, from Yuma to Tempe to Prescott.
Yellow star thistle thrives in full sun and well-drained soil of any type. We recommend applying pre-emergent herbicides in early spring to prevent this weed from germinating. Yellow star thistle is non-toxic.
Learn more about yellow star thistle.
Weed type: Broadleaf
Life cycle: Winter annual
Sun: Full sun
Soil: Well-drained soil
Toxic: Non-toxic
How to identify yellow star thistle: Gray-green leaves and stems. Bright yellow flowers with sharp spines at the base appear from summer to mid-fall. It’s 1 to 3 feet tall.
How to get rid of yellow star thistle: Hand-pulling or hoeing the plants is effective for small infestations. Mow repeatedly and apply post-emergent herbicides with glyphosate or imazapyr for larger infestations. Then, overseed with a desirable turfgrass.
When to hire a pro
Keeping your Arizona lawn lush and healthy is a challenge, regardless of where you live in the state. If you need help with weed control or any lawn maintenance, get in touch with Lawn Love. We connect you with the best pros in Arizona who can take care of your yard while you’re out enjoying all that the Grand Canyon State has to offer.
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Main Image Credit: Joshua Mayer | Flickr | CC BY-SA 2.0
