Ornamental · Poaceae
Mexican Feather Grass
Nassella tenuissima
Settle it into lean soil and full sun, and this soft, swaying grass will reward you all season with almost nothing asked in return.
Full sun
Every 10–21 days
90–120 days
USDA 7–10
Overview
If you have ever felt unsure about grasses, this is a lovely one to start with. Mexican feather grass forgives a lot, and its hair-thin blades catch the smallest breeze and roll in gentle waves. Through the season the green softens to a warm wheat color, and the plant gathers itself into a tidy, fountain shape that looks at home in a gravel bed or tucked along a border.
Think of it as a tough, drought-hardy perennial that grew up in the dry country of the southwest and Mexico, so a little neglect suits it. Once its roots have settled in, it asks for next to nothing and takes heat and poor ground in stride. Do not worry when it quiets down and browns off in the hottest part of summer, because that rest is normal and fresh growth comes back as the weather cools.
The one thing worth your attention is the seed. A single clump can set thousands of wind-borne seeds, and in mild-winter places like California it has slipped past gardens and turned invasive in open grassland. The good news is that the fix is simple and well within your reach: snip the seed heads before they ripen, and this stays a graceful, easy plant you can feel proud of.
Care
The short version: full sun and sharp drainage in lean, sandy soil suit it best. Water lightly once it has settled, leave the fertilizer in the shed, comb it through each late winter, and trim the seed heads before they ripen so it stays politely in bounds.
Light
Treat it to full sun and you will see the truest color and the neatest, most upright clump. A touch of afternoon shade is fine, so do not fret over a slightly shaded spot, but too much and the plant relaxes open and loses that pretty fountain form.
Water
Once it has found its feet this grass is very drought tolerant, so a drink only every 10 to 21 days will do, and even less when things are cool. Give it a good soak now and then through a long dry spell, but please do not let it stand in soggy ground, since wet roots are the one thing it cannot shrug off.
Soil
It is happiest in lean, sharply drained sandy loam, and it copes kindly with rocky or clay ground as long as that ground stays dry. A wide pH band from 5.5 to 8.0 keeps it comfortable, so soil acidity is rarely your worry; it is wetness you want to watch.
Temperature
This is a hardy plant across a wide swing, from about 0°F to 100°F (-18°C to 38°C), which lines up with USDA zones 7 through 10. If your winters dip below that, do not be discouraged, since colder gardens can simply enjoy it as a short-lived seasonal beauty.
Humidity
Dry air is exactly what it likes, coming as it does from arid country. High humidity does it no favors and can even harm the crown by keeping it damp, so give it open space and a little moving air rather than a stuffy, sheltered corner.
Feeding
You can almost forget feeding entirely, which is one less thing to remember. It does well in poor soil, and a light spring feed is the very most it ever wants, since rich ground only makes it floppy and pushes it to throw even more seed.
Pruning
Comb or cut the strawy old blades back in late winter or early spring before fresh growth begins, and try not to mind the ragged look it wears through its summer rest. The kindest, most useful job of all is shearing off the seed heads before they ripen so the plant stays where you want it.
Repotting
In a pot it seldom needs moving, so there is no fuss there, but lift and divide it when roots circle the pot, the middle dies out, or it dries out quickly after every watering. Replant the healthy outer pieces in fresh, gritty mix and let the worn-out center go.
Size & spacing
A grown clump settles in at about 12 to 24 inches (30 to 61 cm) tall and just as wide. Give each one room by spacing plants the same 12 to 24 inches (30 to 61 cm) apart, so every little fountain can arch out without crowding its neighbor.
When to plant
There is no rush and no tricky timing here. Start seed indoors in late winter, six to eight weeks before your last frost, then move young plants outside once the cold has truly passed, anywhere from spring into early summer. The feathery heads show up from June through September, and if you would rather it did not spread, simply 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
Almost everything that goes sideways with this grass comes down to one of two things: the seeding getting ahead of you, or the roots sitting too wet. That worrying brown look in midsummer is usually just the plant taking a nap. Find your situation below and you will know whether a gentle hand is needed or whether you can simply let it be.
Little seedlings turning up everywhere, even beyond the bed
What you are seeing is self-seeding, and it really is the plant's one big drawback. A single clump lets go of thousands of wind-borne seeds that build a long-lasting seed bank and drift off into lawns, paths, and wild ground. You can stay ahead of it easily: cut and bag the feathery seed heads before they ripen, dig out young volunteers roots and all, and bin spent plants rather than composting them where 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 soft, brown, and mushy
Soggy soil is the culprit, bringing on root rot, and this grass simply will not tolerate wet feet. When drainage is poor or watering runs heavy, the crown and roots go soft and dark. Ease off the water and improve drainage, then lift the clump, keep the healthy outer growth, and let the dead center go. Take heart too, since an old plant may just be reaching the natural 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 leaves that look done for by midsummer
More often than not this is simply summer semi-dormancy, the plant's natural way of handling heat, and not a sign of trouble at all. The crown stays alive underneath, and fresh green growth returns once the weather cools or you cut it back. Old dead blades piling up only make it look sadder than it is, so comb them 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 small spots on the leaves
Sticky, distorted foliage usually means aphids are feeding on the blades, while spotting points to leaf spot disease. Neither is anything to lose sleep over. A firm jet of water knocks the aphids off and they rarely return in numbers, and you can simply pull off the worst spotted leaves and open the clump up so air moves through it.
Fix:
- Rinse aphids off with a strong jet of water
- Remove badly spotted foliage and improve air circulation
Toxicity
You can relax on this one. Mexican feather grass is not toxic to cats, dogs, horses, or any other animal, and it is safe around people too. The only small bothers are the bristly seeds, which can tangle in fur or catch in a dog's paw like a foxtail, and the pollen, which may nudge hay fever along in those who are prone to it.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats Safe
There are no toxins here, so a curious cat is in no danger at all. One that chews the blades might bring them back up, and the fine seeds can catch in a long coat, but nothing about it is harmful.
Dogs Safe
Dogs are perfectly safe to be around it and even nibble it. Just keep in mind the bristly awns can tangle in fur and burrow into paws or ears like a foxtail, so a quick brush after a walk through the clump puts things right.
Horses Safe
Horses are in no danger either, since it is not poisonous and is grazed without any harm.
Rabbits Safe
A rabbit can happily nibble the foliage with no risk of poisoning whatsoever.
Livestock Safe
Cattle, goats, and sheep can graze it freely without harm, though it offers them little in the way of real feed value.
Birds Safe
It is harmless to birds, which often pick at the ripe seed and end up helping carry it well beyond your garden.
People Safe
No part of this plant is poisonous to people, so you can handle it with ease. The grass pollen can stir up symptoms in anyone prone to hay fever, which is the only thing to keep in mind.
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 is not a long list to puzzle over here, which keeps things easy. A couple of names show up at the nursery, and one friendly group of look-alikes is worth knowing if you love the look but would rather skip the spreading.
Pony Tails
Pony Tails is the one you will see most often, loved for its especially soft, fine foliage that flows in the lightest breeze, though it self-seeds and wanders just as freely as the species, so keep an eye on it.
Stipa tenuissima (synonym)
Stipa tenuissima is simply the same plant under its older botanical name, which plenty of nurseries still use, so do not be thrown when you find it labeled Stipa rather than Nassella.
Native needlegrasses (Nassella / Stipa species)
Native needlegrasses such as purple needlegrass give you that same airy, dreamy texture without the invasive habit, which makes them the kinder choice wherever the Mexican species causes problems.
How to propagate
Making more of this grass is genuinely simple, and you have two gentle ways to do it. Which one you pick mostly comes down to whether you mind it seeding around.
SeedEasy
Sow indoors late winter to early spring, or it self-sows readily outdoors · One growing season
Seed is the easiest path of all, and honestly the plant does most of the work for you, sprouting all around once it sets seed. Start it indoors in late winter to early spring, or just let it self-sow outside, and within one growing season a seedling fills out into a proper clump. That same eagerness is why it strays where you would rather it did not, so keep the seeding gently in check where it tends to be a problem.
DivisionEasy
Spring · One growing season
Division is the tidy way to make more without scattering seed everywhere, which feels good. Lift an established clump in spring, pull it apart, and throw out any dead center, then replant the living outer pieces and watch them settle in comfortably over a single season.
Myths
Mexican feather grass behaves itself everywhere and never causes any trouble.
In truth it self-seeds hard and is listed as invasive in California and other mild-winter regions, where it hops the garden fence and crowds out native grass in open country. Some areas now discourage or even restrict planting it. None of this should worry you, though, because the answer is simple: cut the seed heads off before they ripen, and where it runs wild, choose a native bunchgrass instead.