Irish moss

Sun

Full sun to partial shade; provide afternoon shade where summers are hot.

Water

Keep evenly moist but not waterlogged. Its shallow roots dry out quickly, especially beside paving.

Soil

Humus-rich, moisture-retentive soil with good drainage; avoid compacted clay and sites that stay wet in winter.

Height

0.1-0.2 ft (0.03-0.06 m)

Spread

0.5-1 ft (0.15-0.3 m)

Flowers

Tiny white, five-petalled flowers in late spring and summer.

Foliage

Evergreen. Fine, narrow, bright to deep green leaves form dense cushions; foliage may brown during severe cold, drought or summer heat.

Growth

Moderate in cool, moist conditions.

Care needed

Medium

• Cold hardy
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Moderate

Toughness

Needs looking after

Pick your zone, country, light and whether you have pets.

1. Planting day

   0 ft (0.01 m)

2. After 1 year

   0.1 ft (0.02 m)

3. After 2 years

   0.1 ft (0.04 m)

4. After 3 years

   0.1 ft (0.05 m)

   full size

About 3 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Growth rate

Moderate

• Water when the soil surface begins to dry; do not let newly planted cushions dry out.
• Work a little compost into the soil before planting; avoid heavy feeding, which encourages loose growth.
• Keep mulch off the foliage and crowns.
• Remove weeds by hand while they are small, before their roots become tangled in the mat.
• Divide crowded or uneven cushions in spring and replant healthy pieces to fill bare patches.

Pruning. No routine pruning or mowing is needed. In spring, trim away dead foliage and lift out dead patches; cut back edges whenever they spread beyond their allotted space.

Spring

Plant or divide cushions once the soil is workable, and water them in thoroughly.

Late spring

Hand-weed between cushions before surrounding growth closes over.

Summer

Check moisture regularly, particularly along paving, and water before the mat dries out.

Early autumn

Repair bare patches with rooted divisions where there is enough mild weather for establishment.

Late autumn

Clear fallen leaves from the mat and check that water drains away freely.

Winter

Avoid walking on frozen or saturated cushions.

• Plant in wide joints between stepping stones on lightly used paths for a soft green contrast to stone.
• Use around small rocks in a cool rock garden, keeping it away from plants that need dry soil.
• Create a small moss-like carpet in a sheltered courtyard with morning sun.
• Edge a moist border beneath dwarf conifers or alongside compact shade-tolerant perennials.

Garden styles it suits: Moss and fern garden, Japanese, Zen dry garden, Alpine rock garden, Cottage garden and Small-space.

Plant it with: Dwarf hostas, Japanese painted fern, Primroses, Dwarf astilbes and Dwarf conifers.

Wildlife: The small flowers may attract small visiting insects, but this is not a major nectar plant. Dense cushions provide shelter for small ground-dwelling invertebrates.

• Summer browning or dieback: check for dry soil and heat reflected from paving; water thoroughly and provide afternoon shade.
• Rot and winter losses: improve drainage and keep crowns out of standing water rather than watering on a fixed schedule.
• Slugs and snails: inspect damp cushions and remove pests; use a labelled iron-phosphate bait if necessary.
• Weeds invading the mat: pull seedlings promptly and remove established weed roots carefully to avoid tearing up the groundcover.

Not known to be toxic to cats, dogs, horses or people; no poisonous parts are established. Species-specific safety information is limited, and it should not be treated as an edible plant.

• Scotch moss (Sagina subulata 'Aurea')

  This is a golden-leaved cultivar of the same species, with yellow-green rather than deep green foliage; its flowers and cushion-forming habit are similar.

• Procumbent pearlwort (Sagina procumbens)

  Usually forms flatter, less cushion-like patches. Its tiny flowers normally have four sepals and absent or very short petals, rather than the conspicuous five white petals of Irish moss.

The species name subulata means awl-shaped, referring to the narrow, pointed leaves, while Irish moss describes its moss-like appearance.

Propagation. Divide rooted cushions in spring or early autumn and keep the pieces moist until established. Seed can be surface-sown in spring; do not bury it deeply.

Accepted botanical name

Sagina subulata

In the US and Canada

Introduced in Hawaii and the lower 48 states.

Sources: GBIF (CC BY 4.0) and USDA PLANTS. The care and design notes are LandscapeGPT's own.