Look Out For These Invasive Plants in Arizona

Salt cedar and noxious grasses are among some of the worst invasive plants in Arizona.
Written by Amber Reed
Reviewed by Melanie Reiff
From Stinknet to Camelthorn, here are eleven of the most invasive and problematic plants in Arizona. 
Abundant plant life might not be the first thing that comes to mind when you think of Arizona, but there are more than 4,000 native species of plants in the Grand Canyon State. Unfortunately, there are also a lot of non-native species that displace the locals and disrupt the natural ecosystem.
 If you own property in Arizona or are thinking of moving there, it’s wise to be on the lookout for invasive plant species that could mean damage not just to the ecosystem, but also to your home and property value. 
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The top 3 invasive plant species in Arizona

1. Buffelgrass

Scientific name: Cenchrus ciliaris/Pennisetum ciliare
What it looks like: Fairly large, ragged bunchgrass with leaves that are brown in the winter and green in the summer. It produces many small bristly seedheads, which are wind-dispersed. 
Why it’s a problem: These plants form dense patches that are difficult to eradicate, and take space and water resources away from native plants. Additionally, Buffelgrass gets bone dry and provides major fuel for wildfires. 
What to do: This plant presents a serious fire hazard to homeowners, so any Buffelgrass should be completely removed by pulling or digging up the plant. Dispose of the plant entirely and make sure no seeds are left behind. Seeds can lay dormant in the soil for years, so monitor for regrowth. 

2. Fountain Grass

Scientific name: Cenchrus setaceus/Pennisetum setaceum
What it looks like: Large bunchgrass with long, slender blades and pink, purple, or brown colored bottle-brush-like stalks.
Why it’s a problem: Fountain Grass is quite pretty, and was initially introduced in the 1940s for extensive use in landscaping. They’ve now run amok and are no longer permitted to be sold or planted. Like Buffelgrass, Fountain Grass competes with native plants for resources and poses a fire hazard. 
What to do: Manual removal and disposal—much like Buffelgrass—with close monitoring for any stray seeds. Targeted herbicides can be used as well.

3. Stinknet (aka Globe Chamomile)

Scientific name: Oncosiphon piluliferum
What it looks like: Small winter annual with dark green leaves and a distinctive, bright yellow, ball-shaped flower.
Why it’s a problem: This one is a new offender, having just been declared an official Arizona noxious weed in 2020. It can quickly overtake a landscape and its dry parts are extremely flammable. They can cause serious allergic reactions when growing, and yes—they stink. Reports have likened it to a strong turpentine odor, and they produce acrid smoke when burned.  
What to do: Dig it out immediately if you see it, and wear appropriate protection if you have allergies. It’s important to get this one out before it goes to seed. If it does go to seed, then herbicide will be needed. The Arizona Native Plant Society recommends Glyphosate with MSO surfactant and recommends professionals for thick patches. 
PRO TIP Many plants in the desert have natural cycles of green and brown coloration. If you choose to apply herbicides, make sure you do it when at least 50% of the plant is green. 

Some other notable plant offenders in Arizona

4. Onionweed

Scientific name: Asphodelus fistulosus
What it looks like: Two to three feet high, with leaves that look (but don’t smell) like an onion plant. Flowers have six petals and are small, with white to pink coloring and a brown stripe down the middle of each petal.
Why it’s a problem: Like a lot of now-invasive plants, Onionweed was first introduced for landscaping. Onionweed is quite aggressive and spreads quickly, and takes away space and resources native plants need. It’s also unpalatable to cattle and Arizona wildlife, so once it takes hold there’s not much to keep it in check. 
What to do: Actively remove the plants fully during the growing season. It will likely take repeated efforts, and herbicides may be needed if you choose. 

5. Tree of Heaven

Scientific name: Ailanthus altissima
What it looks like: Smooth grey bark with large, green quill-shaped leaves and red and yellow colored seeds and flowers.
Why it’s a problem: The Tree of Heaven is considered a problem species nationwide and was dubbed a “hellish invasive” by National Geographic. It grows quickly via underground “suckers” and prolific seeds and can kill nearby native plants with toxins excreted into the soil. It also smells bad and can serve as a home to invasive insect species. 
What to do: For starters, don’t plant them. If you have one on your property, it has to be cut down and the stump painted with herbicide. Whether or not you want to consult a priest is entirely up to you. 

6. Scotch Thistle

Scientific name: Onopordum acanthium
What it looks like: Can range from 2 to 12 feet high, with large purple or reddish thistle-like flowers.
Why it’s a problem: It may be the national emblem of Scotland, but it’s not welcome ‘round these here parts. The Scotch Thistle is particularly problematic in cooler northern Arizona, and aggressively crowds out native species. 
What to do: Pulling them out is most effective before they go to seed. The leaves have spines on them, so make sure to wear gloves and long sleeves. 

7. Salt Cedar

Scientific name: Lonicera japonica
What it looks like: Small bush or tree with reddish brown bark and small, scaly flat leaves. Produces small pink or white flowers.
Why it’s a problem: Another good idea gone awry, the salt cedar was introduced in the 1800s for erosion control and landscaping. They have long, deep roots that can penetrate into underground water tables and disrupt the natural aquatic systems. It outcompetes native plants for resources, and serves as fuel for wildfires.
What to do: Don’t plant it. If you do have any on your property, cut them down and treat the cut area with herbicide. 
MORE: Everything you need to know about buying a house in Arizona

8. Yellow Star Thistle

Scientific name: Centaurea solstitialis
What it looks like: Two to three feet tall with ray shaped yellow flowers. 
Why it’s a problem: Like many AZ invasives, this plant uses up resources needed by native plants. It’s also toxic to horses. 
What to do: Consider planting western goldentop or the golden crownbeard instead! If you have Yellow Star Thistle on your property, pull them out by hand or use an herbicide. The Bureau of Land Management often uses controlled burns to combat Yellow Star Thistle, but we do not recommend you try that at home. 

9. Morning Glory 

Scientific name: Ipomoea spp.
What it looks like: Long stems that frequently vine, large heart-shaped leaves, funnel shaped flowers in a variety of colors. 
Why it’s a problem: There are several species of Morning Glory that are classified as noxious weeds in Arizona, and here’s the plot twist: some of them are actually native. Despite their lovely and delicate outward appearance, Morning Glory have thick, aggressive root systems that interfere with and choke out surrounding plants.
What to do: You have to pull out the whole thing, roots and all, which is quite the task. Cutting it back won’t work for long, as it grows quickly. 

10. Sweet resinbush 

Scientific name: Euryops multifidus
What it looks like: This low shrub has thin green leaves that look almost needle-like, and blooms with an abundance of small yellow flowers. 
Why it’s a problem: This plant was introduced in the 1930s to provide grazing for cattle and to help with soil erosion. It’s now considered invasive, as it spreads quickly and pushes out local plants. It gets its name from its smell, which is frequently described as “sweet but disagreeable”. 
What to do: Most effective methods include pulling it out by the roots and herbicide. 

11. Camelthorn 

Scientific name: Alhagi maurorum (A. pseudalhagi)
What it looks like: Creeping shrub with green stems and spines, and reddish seed pods.
Why it’s a problem: This nasty guy has deep roots that spread horizontally and make dense groups of plants. The spines can shoot upwards through asphalt and can puncture car tires. They are also a hazard to animals and people. 
What to do: Camelthorn is exceedingly difficult to get rid of once it’s established, and it’s prohibited to plant it. If you are unlucky enough to have some on your property, experts say that pulling it out will have little effect. You’ve got to go with the herbicides, not once but twice—once when it’s budding and once after regrowth. 
MORE: Cost of living in Arizona
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Invasive plant species aren’t just bad for the plants and animals around them—some can be a risk to people and property. Species like the Buffelgrass pose a severe fire hazard, and our poky pal Camelthorn can ruin your day and your tires. 
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