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Ornamentalornamental grassStraightforward

Mexican feather grass

Nassella tenuissima

A fine-textured hummock of hair-like leaves that moves in the slightest breeze, which is the whole reason to grow it. Short-lived, and it seeds itself around freely enough that it has become a genuine invasive problem in warm dry countries — worth deadheading rather than ignoring.

Position
Full sun
Water
low demand
Drainage
Free-draining
Grows to
40–60 cm × 40–60 cm
Hardiness
H5
Flowers
June to August
Difficulty
Straightforward

August

In flower

Mexican feather grass’s year

Resolved for United Kingdom (general). Every window is stored against a climate event rather than a date, so a late frost pocket runs later than the band shows. What else August calls for.

ActivityJFMAMJJASOND
PlantApril. May.
In flowerJune. July. August.
PruneMarch. April.

Names that cause confusion

stipa — Still sold universally as Stipa tenuissima though it was moved to Nassella. Also confused with Stipa gigantea, golden oats, which is a much larger plant with tall oat-like flower stems.

Timing that travels

The band above resolves this plant's windows into months for one region. These are the windows themselves, stored against a climate event rather than a date — which is the form that survives being carried to a colder garden, a frost pocket, or next year.

Conditions it needs

Light
Full sun
Frost
Hardy
Hardiness rating
H5 (RHS)
Grows best at
12–30 °C
Soil
Sandy, Loam, Chalky
Soil pH
6–7.8
Drainage
Free-draining
Water needs
low
Drought
good tolerance
Waterlogging
poor tolerance
Heat
good tolerance
Wind and exposure
good tolerance
Where these figures come from
LightSourced guidancemoderate confidence
  • Royal Horticultural Society: Mexican feather grass — position

Checked 2026-08-13

FrostSourced guidancehigh confidence
  • Royal Horticultural Society: Mexican feather grass — hardiness

Checked 2026-08-13

Hardiness ratingSourced guidancemoderate confidence
  • Royal Horticultural Society: RHS hardiness ratings

Checked 2026-08-13

Grows best atSourced guidancemoderate confidence
  • Royal Horticultural Society: Mexican feather grass — temperature

Checked 2026-08-13

SoilSourced guidancemoderate confidence
  • Royal Horticultural Society: Mexican feather grass — soil

Checked 2026-08-13

Soil pHSourced guidancemoderate confidence
  • Plant Finder — Missouri Botanical Garden: Nassella tenuissima — culture

Checked 2026-08-13

DrainageSourced guidancemoderate confidence
  • Royal Horticultural Society: Mexican feather grass — soil

Checked 2026-08-13

Water needsHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

DroughtHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

WaterloggingHorticultural consensusmoderate confidence

Winter wet kills it far more often than cold does.

No external citation — see the evidence type above.

Checked 2026-08-13

HeatHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Wind and exposureHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

On your soil

Computed by comparing this plant's recorded requirements against each soil's recorded characteristics. A recorded horticultural fact overrides the comparison where GrowingHQ holds one.

SoilVerdictWhy
Heavy clayWorks, with one conditionMexican feather grass will crop on heavy clay, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. A plant that stays in the ground through winter with its roots in cold, saturated soil rots — which is what kills most of what fails on heavy ground, rather than the cold.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.
SandyPrefers this soilSandy suits Mexican feather grass as it stands: The pH suits it: it wants 6 to 7.8, and this soil is in that range. The free drainage is exactly what it wants. Sandy soil is among the soils it is recorded as suiting. It stands dry conditions better than most, which this soil will test.
Chalky and alkalinePrefers this soilChalky and alkaline suits Mexican feather grass as it stands: The free drainage is exactly what it wants. Chalky soil is among the soils it is recorded as suiting. It stands dry conditions better than most, which this soil will test.
LoamPrefers this soilLoam suits Mexican feather grass as it stands: The pH suits it: it wants 6 to 7.8, and this soil is in that range. The free drainage is exactly what it wants. Loam is among the soils it is recorded as suiting. The soil holds moisture, which saves a great deal of watering.
SiltyPrefers this soilSilty suits Mexican feather grass as it stands: The pH suits it: it wants 6 to 7.8, and this soil is in that range. The free drainage is exactly what it wants. The soil holds moisture, which saves a great deal of watering.
Peaty and acidWorks, with one conditionMexican feather grass will crop on peaty and acid, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. A plant that stays in the ground through winter with its roots in cold, saturated soil rots — which is what kills most of what fails on heavy ground, rather than the cold.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.
Shallow over rockPrefers this soilShallow over rock suits Mexican feather grass as it stands: The free drainage is exactly what it wants. Loam is among the soils it is recorded as suiting. It stands dry conditions better than most, which this soil will test.
Made ground and urban soilWorks, with one conditionMexican feather grass will crop on made ground and urban soil, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. A plant that stays in the ground through winter with its roots in cold, saturated soil rots — which is what kills most of what fails on heavy ground, rather than the cold.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.

Not sure which you have? Four hand tests will settle it.

Space and spacing

Mature height
40–60 cm
Mature spread
40–60 cm
Rooting depth
30 cm
Spacing
30–45 cm apart
Where these figures come from
Mature heightHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Mature spreadHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Rooting depthHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

SpacingSourced guidancemoderate confidence
  • Royal Horticultural Society: Mexican feather grass — spacing

Checked 2026-08-13

How far apart to plant mexican feather grassThree mexican feather grass plants drawn in a row at their recorded spacing of 30–45 cm between plants. The spacing is drawn to scale against a one metre rule; the plants themselves are symbols rather than scale drawings, so the distance between them is the part to read.30–45 cmone metre
Measured centre to centre. Plants set closer than this compete for light and water long before they look crowded, and the crowding cannot be undone once they are in.

Habit and ultimate size

What the plant becomes, rather than what it is when you buy it. The gap between the two is where most planting mistakes live.

Grass and sedge stems comparedTwo stem cross-sections side by side. On the left, a grass stem: a circle with a hollow centre, drawn with a swollen node and leaves arranged in two ranks on opposite sides. On the right, a sedge stem: a solid triangle with no hollow centre, with leaves arranged in three ranks, one from each face. Beneath each, the practical consequence — a deciduous grass is cut to the ground in late winter and regrows; an evergreen sedge is combed through by hand and must not be cut down.Grass (Poaceae)hollowRound stem, hollow centreLeaves in 2 ranksUsually deciduousCut to 10 cm in late winter.It regrows completely.Sedge (Cyperaceae)Triangular stem, solidLeaves in 3 ranksUsually evergreenComb the dead leaves out.Shearing it disfigures it for years.
The stem section is the reliable test in any season. What follows from it is how the plant is cut back, which is where getting it wrong actually costs something.
Foliage
Semi-evergreen — holds its leaves in a mild winter
In a container
Good in a container long-term
Where these figures come from
FoliageSourced guidancehigh confidence
  • Royal Horticultural Society: Nassella tenuissima — foliage

Checked 2026-08-13

In a containerHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Where and how you can grow it

Each way of growing is assessed separately, and “not assessed” is a real answer rather than a gap we have filled in with a guess.

MethodSuitabilityWhat it needs
Open groundWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

Traditional dug bedWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

Raised bedWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

ContainerWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

Growing it

  • PruningRake or comb the dead blades out with gloved fingers in spring rather than cutting the clump down. It is evergreen to semi-evergreen and does not regrow from a shorn base the way a deciduous grass does — a sheared plant looks wrong for the rest of the season and sometimes never recovers.
  • ProtectionCut the flower heads off before the seed ripens if you do not want seedlings throughout the garden. Nassella tenuissima is listed as an invasive weed in Australia and parts of the United States, which is a warning about its behaviour in a warm dry climate rather than a UK legal restriction — but it does seed prolifically here and the habit is worth managing.
Where this guidance comes from
PruningSourced guidancehigh confidence
  • Royal Horticultural Society: Nassella tenuissima — care

Checked 2026-08-13

ProtectionSourced guidancemoderate confidence
  • Royal Horticultural Society: Nassella tenuissima — self-seeding

Checked 2026-08-13

Where to make a pruning cutFour stems compared. The first is cut cleanly on a slope about five millimetres above an outward-facing bud, sloping away from it, and is labelled correct. The second is cut too far above the bud, leaving a long stub that dies back. The third is cut too close, into the bud itself, which loses the shoot. The fourth is cut sloping towards the bud so rain runs onto it rather than away, which rots it. In every case the bud points outwards, away from the centre of the plant.Correct5 mm, sloping awayToo highstub dies backToo closebud lostSloping inrain sits on the bud
The bud you cut to becomes the new shoot, and it grows in the direction it points — which is why an outward-facing bud opens the plant up and an inward-facing one crosses the middle.

Sources for this page

GrowingHQ editorial synthesis · Plant Finder · Royal Horticultural Society

Each figure on this page carries its own citation, under the “where these figures come from” note in its section. Record last reviewed 2026-08-14.