Irish moss
Sagina subulata · Caryophyllaceae
A dense, emerald-green cushion that looks like moss but is a flowering plant, dotted with tiny white stars in late spring. It tolerates light foot traffic.
- Size
- 1 in tall, 12 in wide
- Zones
- 4 to 8
- Light
- Full sun to part sun
- Flowers
- Mid May to late June
- Pets
- No toxicity recorded
- Job in a bed
- Carpet
A bed built around Irish moss
The planner designed this bed around Irish moss when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border in zone 6, full sun. It chose the other plants from the 966 that suit those conditions, and says below why Irish moss stands where it does.
The plants
- 1 Irish moss × 32, white
- 2 Carpathian bellflower × 8, blue
- 3 False sunflower 'Summer Sun' × 3, yellow
- 4 Brown-eyed Susan × 3, yellow
- 5 Globe arborvitae 'Danica' × 1, green leaves
- 6 Chives × 8, purple
- 7 Hardy gladiolus × 4, pink
Why this plant
- The only white. White sits between stronger colours and calms them.
Why here
- Under the taller plants. It runs back between them as living mulch: there its job is to cover the soil, not to be looked at.
- 32 plants in 8 groups (5, 5, 5, 5, 3, 3, 3 and 3). Seen again further along, the same plant ties the bed together.
Why now
- In flower for 7 weeks. From mid May to late June.
- Part of the bed's peak. With chives and hardy gladiolus in late May: 3 kinds at once. No week has more.
- One of two evergreens. They are what the bed has to show from November to March.
Planned as an English border: 6 of the 7 groups (86%) are drifts, longer along the bed than they are deep. The scheme leans cool (blue, purple and pink) and uses yellow for warmth, with white to calm things between them. Irish moss is planted in 8 places along the bed, which gives it rhythm.
The planner's own design check: 11 Excellent, 6 Good. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where Irish moss goes in a border
At 1 in it belongs at the front of a bed. In the planner's ten height classes it is ground-hugging (up to 6 in).
Its job: carpet. A groundcover planted in threes and fives to cover the soil: along the front, and just behind it.
It gives the look of a moss garden where real moss would burn. It needs even moisture and good drainage: it browns in drought and rots in wet clay.
- Between stepping stones
- A moss effect in sun
- Small-scale groundcover
What to plant with Irish moss
Plants recorded as good partners for it, and what each pairing does:
- Blue star creeper: in flower together for six weeks, from late May; tall enough (3 in) to stand behind it; happy in the same moist soil.
- Mazus: in flower together for five weeks, from mid May; tall enough (2 in) to stand behind it; happy in the same moist soil.
- Black mondo grass: its black leaves are a setting for the flowers, before and after; spires rising out of its mound; tall enough (8 in) to stand behind it.
Questions about Irish moss
Does Irish moss need sun or shade?
Irish moss 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 Irish moss 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 Irish moss flower in my zone?
In zone 5 it flowers mid May to late June. As a spring flower it moves about a week for every zone: earlier where it is warmer, later where it is colder.
| Zone 4 | Late May to early July |
|---|---|
| Zone 5 | Mid May to late June |
| Zone 6 | Early May to late June |
| Zone 7 | Early May to late June |
| Zone 8 | Late April to late June |
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 Irish moss be planted?
8 in (20 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 12 in (30 cm), so a group knits into one patch.
It grows 1 in (3 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many Irish moss plants do I need?
At 8 in apart, set out in staggered rows:
- 27 to fill 10 square feet (about 1 m²)
- 16 for a single row 10 ft (3 m) long
- 86 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as threes and fives, along the front and just behind it.
In the bed above, the planner used 32 in eight groups.
Is Irish moss 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 Irish moss?
Irish moss comes from Chile to Argentina and the Falkland Islands. These North American natives come closest to doing its job:
- Common blue violet: the same job in a bed and the same colour; 7 in taller, flowers mid April to late May.
- Blue-eyed grass: the same flowering time; an edging, not a carpet, 13 in taller.
- Iceland poppy: the same flowering time and the same colour; a drift, not a carpet, 15 in taller.
Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.
Do deer eat Irish moss?
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 Irish moss?
Irish moss is over by late June. These start as it finishes and carry the same spot on, so it never goes flat:
- Black-eyed Susan: from mid July to mid September, 24 in tall.
- Butterfly weed: from late June to early August, 24 in tall.
- Carpathian bellflower 'Blue Clips': from late June to late August, 8 in tall.
What does Irish moss look like in winter?
Irish moss keeps its green leaves all winter, so it is one of the plants that hold a bed together from November to March, when the perennials have gone.
In these guides
- Plants you can walk on
- Pet-safe plants for a sunny border
- Low plants for the front of a border
- Groundcover plants
- Evergreen perennials, ferns and grasses
- Plants for a white garden
Every fact on record
- Type
- Perennial (groundcover)
- Size
- 1 in (3 cm) tall, 12 in (30 cm) wide
- Plant
- 8 in (20 cm) apart
- Height class
- Ground-hugging (up to 6 in)
- Place in the bed
- Front
- Flowers
- Mid May to late June; white
- Leaves
- Fine texture, evergreen; green
- Shape
- Mat-forming, spreading
- Hardy in
- USDA zones 4 to 8
- Light
- Full sun, part sun
- Soil
- Average, evenly moist
- Water
- Moderate
- Feeding
- None needed
- Family
- Caryophyllaceae
- Comes from
- Chile to Argentina and the Falkland Islands
- Stands up to
- Foot traffic
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.