Ornamental · Poaceae
Mexican Feather Grass
Nassella tenuissima
Pop it in lean soil and full sun and this breezy grass pretty much takes care of itself, as long as you watch the seed.
Full sun
Every 10–21 days
90–120 days
USDA 7–10
Overview
Mexican feather grass is the one that's always moving. Those hair-thin blades catch even a whisper of wind and roll like water, and they shift from green to a warm wheat color as the season wears on. It keeps itself in a neat, fountain-shaped clump, so it looks great in a gravel garden and just as good woven through a border. What's not to like?
It's a tough, drought-hardy perennial from the dry country of the southwest and Mexico, which tells you everything about how little it needs. Once it's rooted in, it barely asks for a thing and just shrugs off heat and poor soil that would stop fussier plants cold. And don't panic when it browns off and goes quiet in high summer, because that's just it taking a breather before it greens back up when things cool down.
So what's the catch? It's the seed. One clump can fling out thousands of wind-borne seeds, and in mild-winter spots like California it's hopped the garden fence and gone invasive in open grassland. Stay on top of it, snipping the seed heads before they ripen, and it's a graceful, no-trouble plant. Ignore it, though, and it'll turn up where you never invited it.
Care
The short version: it wants full sun and sharp drainage in lean, sandy soil. Water it sparingly once it's settled, forget the fertilizer, comb it out every late winter, and clip off the seed heads before they ripen so it stays put.
Light
Give it full sun and you'll get the best color and the tightest, most upright clump. A bit of afternoon shade won't hurt, but pile on too much and the plant just flops open and loses that nice fountain shape.
Water
Once it's settled in, this grass is very drought tolerant and only wants a drink every 10 to 21 days, even less when it's cool out. Give it a good soak now and then through a long dry spell, but don't ever let it sit in soggy ground, because that's what rots the roots.
Soil
It loves lean, sharply drained sandy loam, and it'll cope with rocky or clay ground too, as long as that ground stays dry. It's easygoing about pH across a wide 5.5 to 8.0 range, so acidity is hardly ever the problem; it's wetness you've got to keep an eye on.
Temperature
It's hardy across a big swing, from about 0°F to 100°F (-18°C to 38°C), which lines up with USDA zones 7 through 10. Drop below that in a hard winter and it won't make it, so colder gardens are better off treating it as a short-lived seasonal plant.
Humidity
Dry air suits it just fine, since it's a desert kind of plant at heart. High humidity does nothing for it and can even cause trouble by keeping the crown damp, so give it some open space and moving air instead of a stuffy, sheltered corner.
Feeding
You can basically skip feeding altogether. It does great in poor soil, and a light spring feed is the most it'll ever want, if even that, because rich ground just makes it floppy and pushes out even more seed.
Pruning
Comb or cut the strawy old blades back in late winter or early spring before the new growth kicks in, and don't sweat the ragged look it gets during its summer rest. The job that really counts is shearing off the seed heads before they ripen, which keeps it from wandering.
Repotting
In a pot it hardly ever needs moving, but lift and divide it when the roots start circling, the middle dies out, or it dries out fast after every watering. Replant the healthy outer pieces in fresh, gritty mix and just toss the worn-out center.
Size & spacing
A grown clump tops out around 12 to 24 inches (30 to 61 cm) tall and about the same across. Set your plants the same 12 to 24 inches (30 to 61 cm) apart so each little fountain has room to arch out without bumping into its neighbor.
When to plant
There's nothing fiddly about the timing here. Start seed indoors in late winter, six to eight weeks before your last frost, then move the young plants outside once the cold's gone for good, anywhere from spring into early summer. Those feathery heads turn up from June through September, and if you'd rather it didn't spread, just snip them off before they ripen.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Late winter to early spring, 6-8 weeks before last frost
- Plant: After last frost, spring through early summer
- Harvest: June to September
Hardiness
USDA hardiness zones: 7–10
Temperature: down to -18°C
Troubleshooting
Honestly, most of what goes wrong here is one of two things: the seeding running away with itself, or the roots sitting too wet. And that scary-looking browning in midsummer? That's usually just the plant resting. Find what matches below and you'll know whether to step in or leave well enough alone.
Seedlings turning up all over, even past the garden edge
That's self-seeding, and it's hands down the plant's biggest downside. One clump tosses out thousands of wind-borne seeds that build a long-lived seed bank and drift off into lawns, paths, and wild ground. Cut and bag the feathery seed heads before they ripen, dig out the young volunteers roots and all, and bin the spent plants instead of composting them anywhere the grass runs wild.
Fix:
- Cut off and bag the feathery seed heads before they ripen and shed seed
- Pull or dig volunteer seedlings while young, including the roots
- Remove and dispose of spent plants in the trash, not compost, where invasive
The middle of the clump going brown and mushy
Soggy soil's behind this, bringing on root rot, and this grass has zero tolerance for wet feet. When drainage is poor or the watering's too heavy, the crown and roots go soft and dark. Ease off the water, sort out the drainage, then lift the clump, keep the healthy outer growth, and ditch the dead center. Sometimes, though, an old plant is just reaching the end of its short life.
Fix:
- Improve drainage and reduce watering
- Lift and divide healthy outer portions, discarding the dead center
- Replant in sharply drained, lean soil
Strawy, brown foliage that looks dead by midsummer
Nine times out of ten this is just summer semi-dormancy, the plant's normal way of handling heat, not anything to worry about. The crown's still alive underneath, and fresh green growth comes back once it cools off or you cut it down. All that old dead blade piling up just makes it look worse, so comb it out by hand or rake and shear the clump in late winter.
Fix:
- Comb out dead blades by hand or rake
- Cut foliage back in late winter to early spring to refresh growth
Sticky blades, twisted growth, or little leaf spots
Sticky, distorted foliage usually means aphids are at the blades, while spotting points to leaf spot disease. Neither one's a big deal, honestly. Blast the aphids off with a strong jet of water and they rarely come back in any number, and you can just pull off the badly spotted leaves and open the clump up so air can move through.
Fix:
- Rinse aphids off with a strong jet of water
- Remove badly spotted foliage and improve air circulation
Toxicity
Good news if you've got pets: Mexican feather grass is not toxic to cats, dogs, horses, or anything else, and it won't hurt people either. The only real nuisances are the bristly seeds, which can tangle in fur or catch in a dog's paw like a foxtail, and the pollen, which might set off hay fever in folks who get it.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats Safe
There's nothing toxic here, so a nosy cat is totally fine. One that chews the blades might bring them back up, and the fine seeds can catch in a long coat, but that's about it.
Dogs Safe
Dogs are safe to hang around it and even nibble it. Just remember the bristly awns can tangle in fur and burrow into paws or ears like a foxtail, so give them a quick brush after a walk through the clump.
Horses Safe
Horses are fine with it too, since it's not poisonous and they graze it without any harm.
Rabbits Safe
A rabbit can nibble the foliage all it likes with no risk of poisoning.
Livestock Safe
Cattle, goats, and sheep can graze it freely, though it doesn't offer them much real feed value.
Birds Safe
It's harmless to birds, which love to pick at the ripe seed and end up helping carry it way beyond the garden.
People Safe
No part of the plant is poisonous to people, so handling it is no problem. The grass pollen can set off symptoms in anyone who's prone to hay fever, though, so that's worth a heads-up.
The fine, bristly seeds and awns can cling to and tangle pets' coats (a minor foxtail-type mechanical nuisance), and pets that nibble grass may vomit. Grass pollen may bother allergy-prone people.
Varieties
There isn't a whole lot to choose from beyond the plain species, which keeps things simple. A couple of names pop up at the nursery, and there's one group of look-alikes worth knowing if you love the look but could do without the spreading.
Pony Tails
Pony Tails is the one you'll see for sale most, loved for its unusually soft, fine foliage that flows in the lightest breeze, though it self-seeds and runs just as freely as the species does.
Stipa tenuissima (synonym)
Stipa tenuissima is the exact same plant under its older botanical name, and since plenty of nurseries still use it, you'll often find the grass labeled Stipa rather than Nassella.
Native needlegrasses (Nassella / Stipa species)
Native needlegrasses like purple needlegrass hand you that same airy texture without the invasive streak, which makes them the smarter pick wherever the Mexican species causes trouble.
How to propagate
Want more of it? You've got two easy ways to go, and it mostly comes down to whether you mind it seeding around the place.
SeedEasy
Sow indoors late winter to early spring, or it self-sows readily outdoors · One growing season
Seed is the easy route, and let's be honest, the plant does most of the work itself, sprouting all over once it sets seed. Start it indoors in late winter to early spring, or just let it self-sow outside, and a seedling fills out into a proper clump within one growing season. That same eagerness is exactly why it spreads where you don't want it, so keep the seeding in check anywhere it's a problem.
DivisionEasy
Spring · One growing season
Division is the clean way to get more without scattering seed everywhere. Lift an established clump in spring, pull it apart, throw out any dead center, then replant the living outer pieces, and they'll settle in over a single season.
Myths
Mexican feather grass is a well-behaved ornamental no matter where you plant it.
Not quite. It self-seeds hard and is listed as invasive in California and other mild-winter regions, where it jumps the garden fence and crowds out native grass in open country. Some areas have even started to discourage or flat-out restrict planting it. So here's the deal: cut the seed heads off before they ripen, and where it runs wild, go with a native bunchgrass instead.