Mexican feather grass is an unusually delicate, airy desert plant, but don’t let its appearance fool you. It’s surprisingly tough and reseeds aggressively. Here’s how to grow this desert native.
Mexican feather grass (Nassella tenuissima) is a southwest native ornamental grass that’s delicately beautiful, a description that rarely applies to desert plants.
Everything about this plant is light and airy. It has slender, almost thread-like, bright green leaves. Its soft, silvery inflorescences sway in the slightest breeze which has a softening, cooling effect in the garden.
But this native grass is much tougher than it looks, which can be a benefit and a problem.
It withstands our desert sun and temperature extremes and only needs a low-to-moderate amount of water to keep it looking fresh. But it puts out thousands of seeds and may not stay where you plant it.
Why I Like This Plant
- Beautiful bright green leaves and silver plumes
- Delicate, light, and airy — rare attributes in desert plants
- Low-maintenance desert native
- No thorns, non-toxic
Things to Watch Out For
While individual plants are relatively short-lived, plants reseed readily, sometimes aggressively. It is considered invasive in California and is potentially invasive in other parts of the southwest.
Optimal Growing Conditions
If you’re thinking of adding Mexican feather grass to your garden, you need to find a suitable place that will keep your plant healthy and looking good… while minimizing maintenance for you.
Here are key factors to keep in mind.
Temperature
Mexican feather grass should be grown in USDA Hardiness Zones 7 – 11. It handles extreme heat and is cold-hardy down to around -10°F.
Sun Exposure
Mexican feather grass is happy in either full sun or part shade. In the hottest lower desert climates, plants appreciate some dappled shade.
Size and Growth Rate
Mexican feather grass is a fast grower that stays a manageable size of 2 feet tall by 2 feet wide.
Soil
Mexican feather grass is not particular about soil. It grows in sandy, rocky, or clay soil, provided it’s well-draining.
Other Location Considerations
Because it has no thorns and produces minimal litter, it’s a plant you can feel comfortable placing near a pool or sidewalk, or anywhere it might come in contact with pets and people. (The only time it’s messy is when it’s time to prune.)
But you can expect that anyone walking by will be tempted to run their hands over the silky inflorescences! Fortunately, they are not spiky, irritating, or toxic.
Because of its relatively small size, Mexican feather grass is a good choice for narrow spaces or containers.
It can be planted on banks or slopes for erosion control.
If possible, plant where the sun will shine behind it at least part of the day, since it glows beautifully when backlit.
Mexican Feather Grass:
The Essentials
| Common Name | Mexican feather grass |
| Scientific Name | Nassella tenuissima |
| Origin | Texas, New Mexico, Mexico |
| Plant Type | Bunch grass |
| USDA Zones | Zones 7 – 11 |
| Cold Hardy | To -10℉ |
| Flower Color | White |
| Flower Season | Summer |
| Mature Size | 2’ high x 2’ wide |
| Growth Rate | Fast |
| Sun Tolerance | Full sun, part shade |
| Water Needs | Low to moderate |
| Pests & Diseases | None |
| Garden Friendly | No thorns, non-toxic |
| Concerns | Potentially invasive |
| Wildlife | Deer, rabbit resistant |
How to Plant
The rule of thumb when planting any ornamental grass is to dig a hole three times as wide as the root ball but no deeper. Amending the soil is not recommended. Counterintuitively, backfilling with the same native soil you just dug up helps your plant develop a stronger root system.
When to Plant
The best time to plant Mexican feather grass is in the fall. This gives your grass three seasons to grow roots and get established before the following summer.
The second best time is in spring, the earlier the better. This still gives your plant time to get established before the intense heat of June arrives.
How to Care for Mexican Feather Grass
Whether you’ve recently planted Mexican feather grass or have an existing plant in your yard, here’s how to take care of it to keep it healthy and looking its best.
How to Water New Plants
As a southwest native, Mexican feather grass needs very little water once established, but it does need regular watering after being planted.
Here is the recommended watering schedule for new ornamental grasses.
| Weeks 1 & 2 | Every 3 – 4 days |
| Weeks 3 & 4 | Every 6 – 7 days |
| Weeks 5 & 6 | Every 7 – 10 days |
| Weeks 7 & 8 | Every 10 – 14 days |
How to Water Established Plants
Once your Mexican feather grass is established, water it deeply every few weeks during the summer.
Since plants go dormant in the winter, they only need water once a month, which is typically provided by winter rains.
Overwatering can cause root rot. So can the use of organic mulch.
Should You Fertilize?
There is no need to fertilize Mexican feather grass since it gets all the nutrients it needs from native soil.
How to Prune
Mexican feather grass should be pruned hard once in late winter or early spring. Cut it down to 3 – 4 inches above the ground.
You can cut it straight across, but slightly irregular cuts look more natural and mimic the grazing that would occur when growing in grasslands. This lets light penetrate the crown and makes way for new spring growth.
To prevent any possibility of reseeding, cut back the seed heads before they ripen.
Pro Tip!
Tightly tie the dried leaves and flower stalks
with string or duct tape before cutting.
This makes clean-up much easier.
Is It Aggressive or Invasive?
Mexican feather grass may or may not behave in your garden. I’ve heard conflicting reports that range from “it reseeds a bit” to “it reseeds aggressively.”
My HOA planted many of these and I now see them popping up in common areas adjacent to our community, so my experience is that they are fairly aggressive.
But is it actually invasive?
It has already naturalized in many regions of the world including those as diverse as the United Kingdom, Italy, New Zealand, Spain, Switzerland, and South Africa. It’s considered an invasive species in Australia, where it threatens the Eucalypt Woodlands.
It’s already considered an invasive species in California, especially in the southern part of the state and in the San Francisco area. Each plant produces tens of thousands of seeds, which are dispersed by wind, water, and animals.
According to the Lady Bird Johnson Wildflower Center, its natural range only covers the mountains in west Texas and adjacent New Mexico. In areas outside its natural range (i.e., the rest of the southwest), it has the potential to become invasive.
Arizona State University also acknowledges that Mexican feather grass has the potential to become invasive in the grasslands of Arizona.
For these reasons, I won’t plant it in my yard (even though I love the way it looks). I don’t want to risk contributing to any more grass invasions in the Sonoran Desert. (We already have enough problems with buffelgrass and fountain grass.) I’ll stick with non-aggressive natives such as sideoats grama or bull grass.
Pro Tip!
Tightly tie the dried leaves and flower stalks
with string or duct tape before cutting.
This makes clean-up much easier.
Plant Lover Facts
Mexican feather grass has a few alternative common names including silky thread grass, Mexican needle grass, Texas needle grass, and, my pony tails.
Its current scientific name is Nassella tenuissima, but it is still often referred to by its former name, Stipa tenuissima.
It’s native to the desert southwest, but unexpectedly, it also has separate native populations in Argentina and Chile.
Have you grown this plant?
Was it a “hit” or a “miss” in your garden?
Please share your experience in the comments below!
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for 15 years.
