Frost grass
Spodiopogon sibiricus · Poaceae
Leaves held out horizontally from upright stems give it the look of a small bamboo. Airy, purplish plumes open in late summer, and the leaves turn wine red in autumn.
- Size
- 4½ ft tall, 2½ ft wide
- Zones
- 4 to 8
- Light
- Full sun to part sun
- Flowers
- Late July to early September
- Pets
- No toxicity recorded
- Job in a bed
- Specimen
A bed built around frost grass
The planner designed this bed around frost grass when this page was made: a 12 × 6 ft (3.7 × 1.8 m) naturalistic planting in zone 6, full sun. It chose the other plants from the 966 that suit those conditions, and says below why frost grass stands where it does.
The plants
- 1 Frost grass × 1, purple
- 2 Lingonberry × 8, pink
- 3 Mouse-ear coreopsis 'Nana' × 3, yellow
- 4 Swamp milkweed 'Ice Ballet' × 3, white
- 5 Gray's sedge × 4, green
- 6 Spurge 'Chameleon' × 3, purple leaves
- 7 Asiatic lily × 5, orange
- 8 Meadow saffron × 7, pink
Why this plant
- The only plumes. The others are bells, daisies, flat plates and others. Shape reads at a distance, where colours blur.
- The only purple.
- Part of the bed's structure. Shrubs and grasses keep their shape when the perennials die down. So do lingonberry and Gray's sedge.
Why here
- Anchors a back corner. At 4½ ft it is the tallest plant here, and the tallest close the ends of the bed, where they stand in front of nothing.
- A step in the back row. Next to Gray's sedge (2½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- One plant, alone. A feature plant is seen as an object, and needs clear ground around it.
Why now
- In flower for 7 weeks. From late July to early September.
- Part of the bed's peak. With swamp milkweed 'Ice Ballet' and Gray's sedge in late July: 3 kinds at once. No week has more.
- Stands through winter. Left uncut, it holds its shape until March, when the perennials have gone.
Planned as a naturalistic planting: low grasses and groundcovers, the matrix, make up 54% of the planted ground. The back corners are held by swamp milkweed 'Ice Ballet' and frost grass, the tallest plants on the plan. Cool colours (purple and pink) with yellow and orange as the warm notes, and white and green to calm things between them.
The planner's own design check: 8 Excellent, 8 Good, 1 Satisfactory.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where frost grass goes in a border
At 4½ ft it belongs at the back of a bed. In the planner's ten height classes it is tall (4 to 5 ft).
Its job: specimen. A feature plant with a shape of its own. It stands alone with room around it, and repeats only at a distance.
The horizontal leaves make a distinctive, layered outline. It tolerates part shade and likes moisture; in dry soil it browns early.
- A rounded specimen grass
- Part shade
- Autumn colour
What to plant with frost grass
Plants recorded as good partners for it, and what each pairing does:
- Japanese anemone: in flower together for four weeks, from mid August; happy in the same moist soil.
- New England aster: happy in the same moist soil.
- Joe Pye weed 'Little Joe': in flower together for seven weeks, from late July; bold leaves against its medium ones; happy in the same moist soil.
Questions about frost grass
Does frost grass need sun or shade?
Frost grass grows in full sun (6 or more hours of direct sun a day) and part sun (4 to 6 hours of sun, including some afternoon sun).
It wants soil that stays evenly moist, of average fertility, and a good soak in dry spells.
What zones does frost grass grow in?
USDA zones 4 to 8. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).
Above zone 8 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does frost grass flower in my zone?
In zone 5 it flowers late July to early September. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 4 | Early August to early September |
|---|---|
| Zone 5 | Late July to early September |
| Zone 6 | Late July to early September |
| Zone 7 | Mid July to early September |
| Zone 8 | Mid July to early September |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should frost grass be planted?
24 in (60 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 2½ ft (75 cm), so a group knits into one patch.
It grows 4½ ft (130 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many frost grass plants do I need?
At 24 in apart, set out in staggered rows:
- 3 to fill 10 square feet (about 1 m²)
- 6 for a single row 10 ft (3 m) long
- 10 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as one, with clear ground around it: a feature plant is seen as an object, and a group of them is a thicket.
In the bed above, the planner used one in one group.
Is frost grass poisonous to dogs and cats?
No toxicity is recorded for dogs, cats, horses or people, according to NC State Extension.
"Not toxic" is not "edible": a pet that eats a lot of any plant can be sick.
Is there a native plant like frost grass?
Frost grass comes from Siberia to Japan and China. Southeaster temperate Asia. These North American natives come closest to doing its job:
- Switchgrass 'Heavy Metal': the same size and the same flowering time; an accent, not a specimen, pink, not purple.
- New York ironweed: the same job in a bed, the same flowering time and the same colour; 2½ ft taller, 6 in wider.
- Garden phlox: the same flowering time and the same colour; a drift, not a specimen, 12 in shorter.
Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.
Do deer eat frost grass?
They may. NC State does not list it as resistant to deer or rabbits. Where they visit, protect it, or plant it among ones they avoid.
What flowers after frost grass?
Frost grass is over by early September. These start as it finishes and carry the same spot on, so it never goes flat:
- New England aster: from early September to mid October, 4 ft tall (a recorded partner).
- Garden chrysanthemum: from mid September to late October, 24 in tall, to stand in front of it and cover its fading stems.
- White snakeroot: from late August to mid October, 3½ ft tall, to stand in front of it and cover its fading stems.
What does frost grass look like in winter?
Frost grass turns the colour of straw and, left uncut, stands through the winter. Cut it down in late winter, before the new shoots come up.
In these guides
- Plants that grow near black walnut
- Pet-safe plants for a sunny border
- Tall perennials and grasses for the back of a border
- Plants with purple and burgundy leaves
Every fact on record
- Type
- Grass
- Size
- 4½ ft (130 cm) tall, 2½ ft (75 cm) wide
- Plant
- 24 in (60 cm) apart
- Height class
- Tall (4 to 5 ft)
- Place in the bed
- Back
- Flowers
- Late July to early September; feathery plumes; purple
- Leaves
- Medium texture, herbaceous; green, burgundy
- Shape
- Upright, clumping
- Hardy in
- USDA zones 4 to 8
- Light
- Full sun, part sun
- Soil
- Average, evenly moist
- Water
- Moderate
- Feeding
- Light, in spring
- Family
- Poaceae
- Comes from
- Siberia to Japan and China. Southeaster temperate Asia
- Stands up to
- Black walnut, pollution
Checked against NC State Extension. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.