Ornamental · Poaceae
Mexican Feather Grass
Nassella tenuissima
Thread-fine blades spill into a soft green fountain that turns wheat-gold and trembles at the slightest air.
Full sun
Every 10–21 days
90–120 days
USDA 7–10
Overview
Up close, Mexican feather grass is almost more texture than plant. Each blade is hair-thin, soft, and pliant, finer than a needle and supple enough to bend at the touch of a breath. The blades arch up and spill back over themselves, so the whole clump reads as a loose, flowing fountain of fresh green that shivers at the slightest stir of air.
As the season runs on, that green warms into a pale wheat and straw color, the fine foliage drying to a tawny gold that catches low light. By bloom time the clump throws up airy, feathery seed heads on slender stems, soft plumes that rise just above the leaves and add a hazy, shimmering layer over the green and gold below.
The shape stays neat even as the texture loosens. The plant gathers into a compact, rounded mound of densely packed thread-like blades, roughly as wide as it is tall, with the outer leaves arching toward the ground. Run a hand through it and the foliage feels weightless and silky, every strand fine enough to ripple as a single soft mass.
Care
The short version: these thread-fine blades want full sun and the sharp drainage of lean, sandy soil, only sparing water once settled, no fertilizer, a combing out each late winter, and the feathery seed heads cut before they ripen to keep it in bounds.
Light
In full sun the blades hold their brightest green and the clump stands at its most upright, every thread packed densely together. A little afternoon shade is fine, but in too much the fine foliage slackens and the clump splays open, loosening that tight fountain of leaves.
Water
Once settled the fine roots make this grass very drought tolerant, content with water only every 10 to 21 days and less when the air cools. An occasional deep soak suits a long dry spell, but the thread-like crown rots in wet ground, so it must never sit in it.
Soil
The plant sinks its fine roots best into lean, sharply drained sandy loam, and it manages rocky or clay ground too as long as that ground stays dry. It takes a wide pH range from 5.5 to 8.0, so soil acidity rarely marks the blades; wet soil does.
Temperature
The foliage is hardy across a wide swing, from about 0°F to 100°F (-18°C to 38°C), which covers USDA zones 7 through 10. Cold below that range kills the fine crown, so colder gardens grow it as a short-lived seasonal plant.
Humidity
Dry air keeps the thread-like blades at their best, as suits a plant of arid country. High humidity is no help and can rot the crown by holding it damp among the densely packed leaves, so open space and moving air serve it far better than a sheltered, muggy corner.
Feeding
The fine foliage wants almost no feeding. It thrives in poor soil, and a light spring feed is the most it ever takes, if that, since rich ground makes the slender blades flop and drives still more of the feathery seed.
Pruning
The strawy old blades are combed or cut back in late winter or early spring before fresh threads of growth push up, and the fine foliage looks ragged through summer dormancy. The feathery seed heads matter most, sheared off before they ripen to keep the plant from spreading.
Repotting
In a container the fine roots rarely need moving, but the clump is lifted and divided when roots circle the pot, the center of the mound dies out, or it dries out fast after every watering. The healthy outer threads are replanted in fresh, gritty mix, and the spent middle is discarded.
Size & spacing
A mature mound of these fine blades reaches about 12 to 24 inches (30 to 61 cm) tall and just as wide. Plants sit the same 12 to 24 inches (30 to 61 cm) apart so each soft fountain of foliage can arch fully without tangling into its neighbor.
When to plant
Seed starts indoors in late winter, six to eight weeks before the last frost, and the young plants move outside after the cold passes, from spring into early summer. The fine, feathery flower heads rise above the foliage from June through September, soft plumes on thread-like stems. Cutting them before they ripen holds the spread down.
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
Most of what shows up on this grass is written in the blades themselves: a flush of new seedlings, a soft browning at the heart of the clump, or strawy color across the fine foliage in midsummer. That midsummer fade is usually just the plant resting. Match what you see in the leaves below to know whether to step in.
Fine grass seedlings springing up everywhere, even past the bed
This is self-seeding, the plant's biggest drawback, and the feathery seed heads are the source. A single clump sheds thousands of light, wind-borne seeds that build a long-lived seed bank and drift into lawns, paths, and wild ground. The feathery heads are cut and bagged before they ripen, young thread-fine volunteers are dug out roots and all, and spent plants go in the trash, not the compost, 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 center of the clump going brown, soft, and mushy
Wet soil softens the crown into root rot, and these fine roots have no patience for wet feet. The crown and roots turn dark and mushy where drainage is poor or watering runs heavy. The water is cut back and drainage improved, then the clump is lifted, the healthy outer threads kept, and the dead center discarded. An old mound may also simply be 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 blades that look dead by midsummer
Most often this strawy fade is just summer semi-dormancy, the fine foliage's normal answer to heat rather than a sign of trouble. The crown stays alive beneath the dry threads, and fresh green blades return once the weather cools or it is cut back. Old dead blades caught in the clump make it look worse, so they are combed out by hand or rake, and the clump is sheared 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 threads, or small spots on the foliage
Sticky, distorted blades point to aphids feeding among the fine foliage, while small marks on the leaves signal leaf spot disease. A strong jet of water washes the aphids off the threads, and they rarely come back in number. The worst-spotted blades are pulled, and the clump is opened up so air moves through the dense foliage.
Fix:
- Rinse aphids off with a strong jet of water
- Remove badly spotted foliage and improve air circulation
Toxicity
There is nothing in these fine blades to fear. Mexican feather grass is not toxic to cats, dogs, horses, or any other animal, and it is not poisonous to people. The only catch lies in the seed: the bristly, awned seeds can hook into fur or a dog's paw like a foxtail, and the fine pollen shed by the plumes can bother hay fever sufferers.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats Safe
No toxins run through these fine blades, so a curious cat is in no danger. A cat that chews the threads might bring them back up, and the bristly seeds can catch in a long coat.
Dogs Safe
Dogs are safe around the foliage and may nibble it. The bristly, awned seeds tangle in fur and burrow into paws or ears like a foxtail, so they are brushed out after a walk through the clump.
Horses Safe
Horses are not poisoned by the grass and graze the fine blades without harm.
Rabbits Safe
A rabbit can nibble the soft foliage with no risk of poisoning.
Livestock Safe
Cattle, goats, and sheep graze the thread-like blades freely, though they offer little real feed value.
Birds Safe
It is harmless to birds, which often pick the ripe seed from the feathery heads and help carry it well beyond the garden.
People Safe
No part of the plant is poisonous to people. The fine pollen shed by the plumes can set off symptoms in anyone prone to hay fever.
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
The choices are few, set apart mostly by just how fine and soft the foliage runs. A couple of names turn up at the nursery, and one group of look-alikes shares the same thread-like texture if you want it without the spread.
Pony Tails
Pony Tails is the most widely sold selection, prized for blades even softer and finer than the species, so fine they stream in the lightest breeze, though it self-seeds and spreads just as freely.
Stipa tenuissima (synonym)
Stipa tenuissima is the same fine-bladed plant under its older botanical name, which many nurseries still use, so it often turns up labeled Stipa rather than Nassella.
Native needlegrasses (Nassella / Stipa species)
Native needlegrasses such as purple needlegrass carry the same airy, thread-like texture without the invasive habit, which makes them the better choice where the Mexican species is a problem.
How to propagate
More of this fine-bladed grass comes two ways, and the pick rests mostly on whether you mind the feathery seed scattering. Both are easy.
SeedEasy
Sow indoors late winter to early spring, or it self-sows readily outdoors · One growing season
Seed is the easiest route, and the plant does most of the work itself, the feathery heads scattering thread-fine seedlings all over once they ripen. It is started indoors in late winter to early spring, or it self-sows outdoors, and a single seedling fills out into a soft, rounded clump within one growing season. That same eagerness is why it spreads where it is not wanted, so the seeding is kept in check where it is a problem.
DivisionEasy
Spring · One growing season
Division makes more without scattering the feathery seed. An established mound is lifted in spring and pulled apart, the dead center thrown out, and the living outer threads are replanted, settling into a fresh clump over a single season.
Myths
Mexican feather grass is a harmless, well-behaved ornamental everywhere it grows.
Those soft, feathery seed heads tell a different story. The plant self-seeds hard and is listed as invasive in California and other mild-winter regions, where it jumps the garden and crowds out native grass across open country. Some areas now discourage or restrict planting it. The feathery seed heads are cut off before they ripen, and where it runs wild, a native bunchgrass is the better choice.