Purple Fountain Grass: Sterile or Invasive?

It’s a well-established fact that fountain grass is invasive in the desert. Purple fountain grass is often recommended as a “sterile” variety that can be planted safely instead. But is it truly sterile? And can it become invasive, too?

I love the looks of ornamental grasses. When I lived in Maryland, purple fountain grass was a favorite that I would grow in containers as an annual, since it didn’t survive winters there.

When I moved to Tucson, I was delighted to see that they could be planted in pots or in the ground as a perennial.

I heard repeatedly that fountain grass (Cenchrus setaceus, formerly known as Pennisetum setaceum) was invasive in the Sonoran Desert, but that purple fountain grass was a sterile “safe” variety that had no potential for being invasive.

After all, you can buy it just about anywhere plants are sold. And nurseries wouldn’t sell it if it was invasive… would they?

But I recently learned that purple fountain grass is potentially invasive, too, and that experts warn gardeners not to plant it.

Why Fountain Grass is a Problem in the Desert

You may wonder exactly what’s so bad about fountain grass and whether it’s really necessary to remove your plants. Here are some of the problems fountain grass causes in the desert:

• It grows fast and since it has no natural enemies, it readily out-competes native plants.
• It creates fuel for wildfires. As it dries out, it becomes extremely flammable 🔥, more so than native grasses.
• It blocks the natural flow of water in washes and alters the habitat for animals.
• It provides no benefits to native wildlife or pollinators.

Did you know?
Fountain grass is closely related to buffelgrass (Cenchrus ciliaris),
a highly invasive grass the National Park Service calls
“the archenemy of the Sonoran Desert.”

How Did Fountain Grass Get Here?

Fountain grass seeds were first brought to the desert southwest around 1880. It’s believed fountain grass was planted to prevent erosion.

But more recently, since around 1940, it’s been cultivated as an ornamental plant. Records show that fountain grass began spreading to the Santa Catalina Mountains in 1946.

Fountain grass was officially listed as an Arizona Noxious Weed in 2020 and consequently can no longer be sold in nurseries.

Purple Fountain Grass: What the Experts Say

However, that ban does not apply to purple fountain grass (Cenchrus setaceus ‘Rubrum’) which you can still buy at any nursery or big box garden center. The rationale behind this is that purple fountain grass is purported to be sterile.

I’ve heard and read this repeatedly from many sources, often from nurseries that sell it. I did not question whether this was true and planted a few in my own yard.

So I was dismayed when my arborist pointed out that its sterility has been exaggerated and that plants can still disperse viable seeds which grow outside of cultivation.

Here’s what a few local experts have to say about the sterility of purple fountain grass.

I contacted Ben Tully, Pima County invasive species outreach coordinator, about the invasiveness of purple fountain grass. He advised that gardeners avoid this grass and plant native grasses instead. He also directed me to Saguaro National Park’s website, which states this about fountain grass varieties:

Although some nursery varieties are considered “sterile”, no varieties are recommended for planting and landscaping.

Nurseries may offer “sterile” plants, which are not really sterile, they are just unsuitable for deliberate propagation; these plants still produce a small percentage of viable seeds that can escape and harm our desert.

When I questioned him about why it isn’t on the Arizona Noxious Weed list if it’s known to be problematic. He said that it’s not easy to get a plant on the list. It takes years of lobbying and that nurseries that sell it exert pressure to keep if off the list. 😠

The Desert Botanical Garden in Phoenix concurs, stating this on its website, “Replanting with purple fountain grass may not be a suitable option. This grass is reportedly sterile and does not generally form seeds, but this doesn’t guarantee it won’t.“

The Arizona Native Plant Society has this to say, “Fountain grass comes in many varieties. All should be considered invasive until tested and verified. No variety is recommended for planting.“

Now you might think that it’s unlikely to escape your yard, but seeds are spread by wind, water, and animals. You may even carry them on your clothes or shoes. And after seeds are dispersed, they’re viable in soil for up to 6 years.

I’m as bummed about this as anyone — I had several thriving plants in my yard that I felt obligated to remove. But in view of everything I learned, I accepted that replacing them with something native was the responsible thing to do.

And then I remind myself, it’s not all bad. I get to go shopping for new plants. 😉

What to Plant Instead?

There are plenty of attractive non-invasive ornamental grasses that can take the place of fountain grass in the garden.

You can’t go wrong with native plants and deer grass (Muhlenbergia rigens) should be at the top of your list. It is a southwest native that’s widely considered the region’s most spectacular ornamental grass. In the fall, it sends up elegantly arched 5-foot seed stalks covered in creamy white flowers.

If you have your heart set on a colorful ornamental grass, consider pink muhly grass (Muhlenbergia capillaris )which has gorgeous pink plumes. Note that is an eastern US native, but it thrives in the desert southwest and does not escape cultivation.

Other popular native grasses that look great in desert gardens include big muhly (Muhlenbergia lindheimeri), bull grass (Muhlenbergia emersleyi), and side oats grama (Bouteloua curtipendula).

For more options, check out the list of native grasses at Spadefoot Nursery, a top source of native plants in Tucson.

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Additional Reference

California Native Plant Society

Photo Credits

Arizona Native Plant Society

“Pink Muhly Grass” by Under the Same Moon is licensed under CC BY 2.0