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Irish Moss Plant: Perennial, Plush Ground Cover

If you’re looking for a ground cover that produces tiny star-shaped flowers, look no further than the Irish moss plant. It’s a great addition to a shady rock garden, the spaces between stepping stones, and next to water features. Irish moss (Sagina subulata) can even be a lawn substitute in some areas. 

Its creeping stems tolerate light foot traffic, and as it grows it creates a dense mat that is not only pleasing to the eye but soft on feet. It’s relatively disease-free, too. Growing Irish moss and its cultivar that’s also referred to as golden Scotch moss (Sagina subulata “Aurea”) can add so much dimension to a garden space.

So what do you need to grow a fine-textured carpet of Irish moss or Scotch moss? And what’s the difference between the two? Where do these plants even come from? Well, read on, and we’ll tackle all those questions here. 

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Quick Care Guide

Irish moss plant
Irish moss plant is a lovely, soft ground cover plant. Source: beautifulcataya
Common NameIrish moss, heath pearlwort, awl-leaf pearlwort, Scottish moss
Scientific NameSagina subulata
FamilyCaryophyllaceae family
Height & Spread1 to 2 inches tall, 1 foot wide
LightPartial shade to full sun
SoilAverage to fertile, well-draining
WaterRegular light watering, once per week
Pests & DiseasesSlugs, moles, crown rot

All About Irish Moss

Sagina subulata aurea
Sagina subulata aurea is sometimes called golden Scottish moss. Source: Starr

Irish moss (Sagina subulata) is commonly referred to as heath pearlwort and awl-leaf pearlwort. Scottish moss is technically not the same plant, but it’s a species that is often grown similarly in gardens, although there is a specific cultivar of Irish moss (“Aurea”) that also shares the common name. Both plants are native to Western and Central Europe. You’ll find these moss plants growing on banks and slopes near the fertile coast of the British Isles. But they’re also found anywhere between there and Romania in sandy well-drained soils. A perennial, Irish moss grows only 1 to 2 inches tall and spreads about 1 foot wide. It and the Scotch moss cultivar are often grown in rock gardens, between stepping stones, or as a lawn substitute. Both are members of the carnation family and readily self-sow, creating a lovely mat of soft, green grass-like moss. 

The plant is known as awl-leaf pearlwort because its green leaves are shaped like an awl, a tool used for poking holes in leather or fabric. However, the dense, small clusters of awl-shaped leaves are soft, and the creeping stems don’t reach out to poke anyone. Small, white, star-shaped flowers with five petals bloom in spring at first and then sporadically throughout the growing season.

After each of the white flowers blooms and dies, small brown oblong capsules form, and triangular seeds are produced. These drop from the low-growing plant at a moderate rate, self-sowing as they go. This is how the thin stalks manage to spread out and self-propagate. One of the main differences between Irish moss (Sagina subulata) and Scotch moss (Arenaria verna) is leaf color. Whereas Irish moss has rich green foliage, Scotch moss has gold to chartreuse leaves. Both have white flowers, and both grow similarly. So if you’re looking to fill space in between garden pavers either let color be your guide. 

Planting Irish Moss

Plant Irish moss in spring after the danger of frost has passed. Choose a space in partial shade to full sun with fertile, well-drained soil. This could be on your lawn, in your garden, and even in a walkway where foot traffic is expected. Select a space where you’d like to fill in a gap with low-growing, green foliage, and white flowers.

If you live in an area with drought conditions or extreme heat, plant Irish moss in a container and place that container intentionally in your garden. Make sure the container has rich and well-drained soil that this moss likes. The same timing applies to containers too. Wait until spring when the last frost has passed. To plant this moss (Irish and Scotch varieties), rake about an inch into the soil surface. Then take plugs with adequate roots, and place them on the ground or in your planter. Lightly press the plugs into the soil. You should have no issue getting these plants started from seed too. Either start them indoors in winter a few weeks before the last frost or direct-sow them in spring outdoors. Give them a generous amount of sunlight or grow light. In 2 to 3 weeks, they’ll sprout. 

Care

Irish moss without flowers
A closeup of Irish moss when it’s not in flower. Source: Starr

Once it’s established, Irish or Scotch moss takes off and does well all by itself. Let’s discuss some of the conditions required for growing ground cover of this kind. 

Sun and Temperature

Irish moss prefers full sun to partial shade. In areas where heat gets high, partial shade or shade in the afternoon is a must. Grow Irish moss in an area that gets at least 6 hours of partial shade, and no more than 1 hour of scorching sunlight per day. Ideal Irish moss growing zones include 4 through 8. Scotch moss prefers zones 4 through 7, as zone 8 is too hot for this delicate ground cover.

If you live outside this range, grow Irish moss in a container and bring it in when temperatures dip below 30 degrees Fahrenheit, and above 80 degrees Fahrenheit. Either extreme produces brown patches in Irish moss that can bounce back in fall, restoring it to its lovely green color. Ideally, Irish moss prefers temperatures right around 60 degrees. Because it is low to the ground, using frost or shade cloth may not be as effective as it would be for other plants. This is why ground cover plants need to be selectively placed and situated from the start. 

Water and Humidity

Always water your Irish moss in the morning, before the sun has warmed the ground. Keep the ground around your plant sufficiently moist, but not waterlogged. Especially when it has just been transplanted, it will need a consistent amount of water to root effectively. But light watering with a soaker hose is best for this sensitive ground cover. Insufficient or excessive water causes brown patches. Plants like these prefer rich, moist soil near the coast. That’s one indication that Irish moss is not a drought-tolerant plant.  So keep it evenly moist! If the season has been particularly rainy, do not water your moss plant. Again, excessive water on this low-growing plant will create brown patches rather than the lovely green-colored foliage you’d like in your lawn or garden. 

Soil

Flowering Irish moss
Irish moss in full flower looks like a carpet of green and white. Source: mrburnes99

Grow Irish moss (and its close relative Scotch moss, or Arenaria verna) in soil that is rich, fertile, and well-draining. Think about its native habitat. Native moss plants like to grow on lush coastal hillsides in sandy soil. Underneath the sand, the coast is filled with rich humus soil. So choose an area that is similar to this, or create one in your garden, lawn, or containers. Prepare a mix of compost, rich garden soil, and sand to fill in the area or containers you’ve chosen. Many guides suggest the plant can adapt to poor soils, at least after it’s established. The ideal pH range for Irish moss is 5.6 to 7.5.  

Fertilizing

Irish moss likes a slow-release fertilizer applied to the ground cover once in the spring, annually. But fertilize sparingly, because high nitrogen levels can alter the spread and growth of Irish moss. Instead of growing in a compact and low-lying fashion, with too much nitrogen, it will grow in a mound. Especially if you’re trying to cultivate a garden or lawn with a low ground cover, too much nitrogen is something you want to avoid. Use a full-spectrum 5-5-5 NPK fertilizer, or opt for something that’s slightly lower in nitrogen. This provides adequate nutrition to foliage and flowers without overpowering green growth. 

Pruning

There isn’t much pruning to do with ground cover plants like Irish moss. However, if there are yellowing or brown leaves, remove them as needed. 

Propagation

Propagating Irish moss is easy because it’s a self-sowing plant. Give it a good start in the garden and let it do its thing. Seeds tend to pop out of pods from flowers and help moss plants spread as they would in the wild. However, you can collect seeds and sprout seeds indoors in winter before the last frost. Plant the seeds on the soil surface in a rich starting mix that has a good amount of soilless content included. You can also plant seeds directly in the garden ground or on your lawn. Space the seeds at least 8 inches apart. 

Another way to propagate these plants (outside of seeds) is to divide them from a healthy section of green growth in spring or fall. Simply remove a section of the moss from your garden and pull it apart so that each resulting section has healthy roots. Then place them in partial sun to full sun spots of your garden. Provide adequate moisture to the plants and seeds, and you’ll have more Irish moss plants in your garden, and flowers that bloom in spring. 

Troubleshooting

Sagina subulata
Sagina subulata can tolerate partial shade conditions. Source: Klasse im Garten

When gardening with Irish moss, don’t fret too much if problems arise. Here are a few things to consider, which we have already covered in the previous sections. 

Growing Problems

As mentioned in the fertilizer section, don’t give Irish moss too much nitrogen. This makes it grow into a mound instead of low. High nitrogen could prevent flowering too, which means no seed for self-sowing. Instead, use a full spectrum, balanced, slow-release fertilizer sparingly. 

Remember not to water too much, as this can create brown patches when gardening with Irish moss. The same goes for too little water. If brown patches emerge, no problem. Remove them and let the rest of the patch continue to grow with the correct amount of water. Too much sun causes browning in Irish moss patches too. So if you’re not sure whether or not the space you’ve chosen is too sunny, plant the moss in a container first and move it around as needed, then plant it in the ground once you’re sure of its placement. 

Pests

The only pest Irish moss has to contend with inside the garden is the infamous slug. The easiest way to deal with them in the garden is to give them an intoxicating beer trap. They can’t resist the beer and will perish as they drink. If slugs get out of hand and infest your Irish moss, try an organic slug bait. You should only have to apply this once per season. 

Diseases

Crown rot is the only disease that affects Irish moss. This usually occurs when there is too much water present in the soil, and it’s caused by the same fungal pathogens that cause root rot. Prevention is the best method for controlling crown rot, as it can cause the death of the entire organism. If you notice yellowing leaves in areas where moisture is high, remove them and let the plant dry out. Then apply small amounts of water only after the soil has dried. If this doesn’t improve conditions, remove the entire plant to prevent the spread of fungus to the rest of your garden. 

Frequently Asked Questions

Heath pearlwort
Sometimes referred to as heath pearlwort, the fine leaves are awl-shaped. Source: Futureman1

Q: Where does Irish moss grow best?

A: Irish moss prefers rock gardens, spaces between pavers, or anywhere in your garden ground cover is preferred. Foot traffic is totally ok!

Q: Does Irish moss spread fast?

A: Even though it self propagates by seed, it’s not a vigorous spreader, and it’s easy to remove. There’s no need to worry about planting an aggressive moss. 

Q: Does Irish moss come back every year?

A: In hotter areas, it may get a little scorched in summer and die back in winter. But this perennial will return in temperate seasons. 

Q: Can you walk on Irish moss?

A: Absolutely. Even though the leaf shape is compared to the pokey awl, it’s soft on feet. That’s why it’s often chosen as a ground cover.


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