How to Plant and Grow Irish Moss

Don’t worry about treadling lightly on Irish moss (Sagina subulata). The traffic-friendly groundcover is a smart choice for blanketing the ground around flagstones or along the edges of gravel paths where plants sometimes struggle to grow. What’s more, the handsome, lush, deep green foliage forms a soft, cushy mat that bounces back from occasional damage.

Despite its name, Irish moss is a member of the carnation (Caryophyllaceae) family. It is evergreen in many climates and bears dainty white flowers in spring that emit a light fragrance. It grows just about 1 inch tall and will readily self-sow if you let it. In fact, many golf course professionals, nursery growers, and greenhouse managers consider Irish moss (also known as pearlywort) a bit weedy. When pearlwort pops up in turf grass and other unexpected spots in nurseries and greenhouses, it's sometimes tough to eradicate. In the average home lawn and landscape, however, it is quite easy to remove. 

Where to Plant Irish Moss

Plant Irish moss in full sun (in cooler climates) or slightly shady spots where you want walkable swaths of green. In small yards, it can even be used as a lawn substitute. Too much shade may cause Irish moss to grow leggy; however, in warmer climates, afternoon shade may be a welcome respite.

Irish moss is perfect for creating a barefoot-friendly path or for building a soft carpet of evergreen color among the rough-and-tumble boulders of rock gardens. Its delicate, ferny foliage is also a favorite for fairy gardens or dish gardens. For a stunning effect, plant it in a trough (stock tank) or container planting and let it slowly creep to cover the open soil. 

How and When to Plant Irish Moss

Plant Irish moss plugs or transplants in spring or early summer. Prepare the soil of your planting location by working some compost into the top 6 inches of soil and watering it until it is evenly moist. Using your hands or a trowel, dig a hole just large enough for each plug and just deep enough to accommodate the root system. Fill in the soil around the plug and keep the soil evenly moist (but not wet) for at least 2 weeks after planting.

If you want to cover a large area, collect several plants, and situate them 8 to 10 inches apart. In ideal conditions, they will grow together to form a carpet of color in just a couple of seasons. For a faster cover, plant them closer together.

Irish Moss Care Tips

Irish moss is a low-maintenance groundcover that grows easily in sunny and partially shady areas with moist, well-draining soil. It’s also soft on the feet, pleasing to the eye, and perfect for planting in spots where grass won’t grow.

Light

In cool climates, select a full-sun planting site. In warmer climates (zones 7 and above), plant Irish moss in a spot that receives morning sun and afternoon shade.

Soil and Water

Irish moss grows best in evenly moist, rich, well-drained soil. In water-logged soil, it is likely to fail. If your soil is poor, sandy, loamy, or chalky, consider amending it with organic matter before planting your Irish moss.

Irish moss is more finicky about water than it is about soil. It is not drought-tolerant, so aim to keep the soil consistently moist, but not so wet that the roots stay soggy. In a wet climate (like the Pacific Northwest), Irish moss may not need much supplemental watering during the rainy season. In the summer or in warmer, drier climates, it is likely to need watering every few days. To maximize hydration, water in the morning when the sun is lower.

Temperature and Humidity

Irish moss thrives in cool environments with a temperature between 55- and 65-degrees Fahrenheit. It is not frost tolerant. It tolerates relatively high humidity (60% to 80%) when temperatures remain cool, but prolonged periods of hot, humid weather are likely to cause browning. If you live in a hot, humid climate, don't be surprised if your Irish moss dies out in the heat of summer.

If you are growing Irish moss in a container, bring your container in whenever the thermometer dips below 30 degrees Fahrenheit or climbs above 80 degrees.

Fertilizer

Irish moss needs little (if any) fertilizer. If your soil lacks nutrients, apply a slow-release fertilizer once in the spring. following product label instructions. Avoid fertilizers with a high nitrogen content. Too much nitrogen can cause irregular, leggy growth.

Pruning

It is not necessary to prune Irish moss, but you can trim unruly areas with scissors to keep the sections looking tidy. You can also remove areas that are yellowing or cut out old brown patches to make room for new growth. If unwanted sections appear due to self-seeding, simply pull them up and trim away any stray growth.  

Potting and Repotting

Irish moss grows best in shallow containers where the roots won’t have to struggle for moisture and nutrients. With container-grown Irish moss, it is best to water from the base of your plant. Set it in a tray of water and allow the moisture to absorb through the drainage holes into the soil. This will help prevent fungal diseases and pests.

Repot your Irish moss every 2 to 3 years or when it’s clear that the roots are outgrowing the pot. To do so, ease the plant from its container and use your fingers to gently loosen up the roots and shake some of the soil free. Add fresh soil to the new container, moisten it, and place the plant in the fresh soil. Add additional soil around the edges if necessary. Keep the soil evenly moist for at least 2 weeks after repotting or until the plant is re-established.

Pests and Problems

Irish moss isn’t plagued by many pests, but slugs are often drawn to the plush foliage. If you spot slugs, remove them by hand or steer them away with organic slug bait. Powdery mildew and fungal diseases are also common when Irish moss is over or under-watered.

Indoor and container-grown Irish moss may have issues with aphids, mealy bugs, thrips, and spider mites from time to time.

How to Propagate Irish Moss

The easiest ways to propagate Irish moss is via seed or division. If you wish to grow Irish moss from seed, you can start them indoors at any time or outdoors in the spring after the danger of frost has passed (just watch out for hungry birds). Sprinkle the dust-like seeds on the surface of the soil and do not cover them. Keep the seeds in an area with bright, indirect light that stays between 65- and 75-degrees Fahrenheit. Keep the soil consistently moist. The seeds should begin to germinate in 2 to 3 weeks. Harden off your Irish moss seedlings for approximately 7 days and then transplant them outside after the danger of frost has passed.

To divide your Irish moss, wait until early spring after the plant has had at least one full season of growth. Use a shovel or trowel to lift a clump of your moss and separate the clump into 2 or 3 sections—each with a good number of roots attached. Replant each section and water the newly planted patch well. Keep the new sections evenly moist until new growth emerges.

Types of Irish Moss

Sagina Subulata 'Pearlwort'

‘Pearlwort’ is a traditional Irish moss cultivar that grows bright green with a soft texture and tiny white flowers in the spring and summer (in zones 4-8). It withstands light foot traffic and grows to 1 foot tall or less.

Sagina Subulata ‘Aurea’

Although many people use the terms “Scotch” and “Irish” interchangeably when referring to Sagina sublata varieties, this type of groundcover is more commonly referred to as Scotch or Scottish moss. It forms a dense carpet of neon-yellow foliage and features tiny star-shape flowers in the spring.

Irish Moss Companion Plants

Hosta

If you need a showy plant that will fare well in the understory of trees, a hosta is a classic choice. They are easy to maintain once established and will provide a dramatic backdrop for your low-growing Irish moss.

Foamflower

Foamflower (Tiarella cordifolia) is flowering perennial that—like Irish moss—thrives in partial sun. It is hardy in zones 3-9 and features pink or white blossoms that typically last 4 to 6 weeks. Foamflower is easy to cultivate and there are several shapes and cultivars to choose from.

Creeping Thyme

If you are looking to vary your groundcovers, consider creeping thyme. It’s a close relative to the common culinary thyme (so it is beautifully fragrant) and easy to maintain. Creeping thyme is hardy in zones 4-9 and thrives in full to partial sun. Let it fill the sunnier spots of your landscape while Irish moss occupies the cooler, shadier areas.

Coral Bells

Coral bells prove that gorgeous gardens aren’t always green. This perennial grows well just about anywhere and features foliage in a wide variety of colors including yellow, peach, purple, chartreuse, copper, and green. They are hardy in zones 3-9.