How to Grow and Care for Irish Moss

Irish moss (Sagina subulata) is a low-maintenance groundcover that is perfect for use in rock gardens, between pavers, at the edges of a path, and as a limited-area lawn substitute. Contrary to its common name, this lush and low-growing evergreen perennial only resembles moss—it's actually part of the carnation family (Caryophyllaceae) and has very different growing requirements than actual moss. This is a very hardy but slow-growing plant that can take many months to fill out in the garden but has many practical uses once it's established.

Irish Moss Care

Irish moss is a popular landscaping solution, offering up visual interest and an English garden-like charm. It can tolerate light foot traffic and can be used anywhere carpet-like coverage is desired, such as a rock garden or even a lawn where it's difficult to grow grass. Unlike true moss, Irish moss doesn't do well in full shade or in wet conditions. It prefers a sunny or partially shady position and doesn't like intense heat. In the right conditions, though, this plant grows well and adds a rich and dense spread of color to your garden. Plant Irish moss in the spring after your average last frost date—in generally, the seeds should take about two to three weeks to sprout and will establish shortly thereafter.

Light

Irish moss grows best in full sun or partial shade. If you live in a zone with high heat, try planting your Irish moss in an area that gets afternoon shade, though too much shade results in the plant becoming leggy, losing some of its compact quality, and developing less attractive mounds.

Soil

Irish moss prefers good quality soil that is rich and fertile. That being said, it can adapt to sandy, loamy, and chalky soils, provided they're packed with nutrients. You may need to add organic matter to help it survive in areas where the summers are hot and dry, or if the soil isn't particularly fertile. Irish moss doesn't do well if the soil becomes water-logged, so ensure that you plant it in a spot that does not have sitting or retained water.

Water

It can be tricky to get the watering levels right with Irish moss. If you go too far in either direction, brown patches can develop. In general, you should aim for soil that is consistently moist but never waterlogged. Water your Irish moss in the morning to avoid any premature evaporation—a soaker hose set to a mild rainfall setting (versus a heavy jet) is preferred. Keep in mind, Irish moss isn't at all drought-tolerant, so it will need consistent watering every few days, depending on the heat.

Temperature and Humidity

Irish moss is fully hardy in USDA Zones 4 to 8. This ground cover will struggle when planted in areas that experience intensely hot or dry summers—if you live beyond its ideal hardiness zones and want to grow Irish moss, it is best done in a container that can be moved into the shade when necessary.

Fertilizer

Use a slow-release fertilizer annually in the springtime to help your Irish moss grow to a tidy, uniform 1 to 2 inches in height. You should opt for a balanced 5-5-5 NPK fertilizer or even a slightly lower nitrogen formula. If Irish moss receives too much nitrogen due to overfertilization, it can result in an irregular growth pattern, developing in an undulating shape rather than a compact and low-growing form.

Pruning

Pruning Irish moss is not necessary, though you might want to trim the plant back from steps, pavers, and other structures to keep the area looking neat. If you choose to do so, you can use clean scissors or sheers to trim it. Otherwise, Irish moss will perform best if left to grow freely.

Propagating Irish Moss

To propagate Irish moss, divide it in early spring so it has the entire growing season to get established. Division is also a good way to thin out and rejuvenate an Irish moss patch if some of the mounds have become unsightly, browned, or have failed to flourish over time.

1. To divide the plant, lift out the entire clump with a shovel.
2. Separate the clump into smaller sections using a shovel (or pruners, if the clump is small). Make sure that each section has decent roots attached.
3. Replant the sections in a new location, burying them to the same depth as the original plant.
4. After replanting the moss, go back and trim any wayward stems. Water the newly-planted patch well and keep the plants moist until you see new growth begin to establish.

How to Grow Irish Moss From Seed

It is possible to sow Irish moss directly in the ground in the spring. However, because birds like to eat the seeds, it's better to start Irish moss in seed flats indoors about one month before your last average frost date. To do so, lightly press the seeds into the soil but do not cover them, as they need light to germinate. Kept the flat moist at all times and at a temperature between 55 and 60 degrees Fahrenheit. Harden off the seedlings before transplanting them outdoors after the last spring frost.

If you already have Irish moss established in your landscape, we have good news: It will self-seed regularly, eliminating any need to plant additional seeds. If you want Irish moss in a spot that it hasn't naturally spread to yet, you can propagate it using the method outlined above.

Potting and Repotting Irish Moss

Although it is mostly grown as a groundcover, Irish moss is also suitable for container growing. It will look best planted in a pot that is wide and shallow, which will help accentuate its natural spread. Fill the container with potting mix and keep the plant well-watered at all times. It's helpful to choose a pot made of terracotta or clay, which will naturally wick any excess moisture away from the soil and prevent the Irish moss from getting waterlogged. Potted Irish moss will need repotting about every three years, or when it outgrows its container.

Overwintering

Irish moss is cold-hardy to USDA zone 4 and can survive the winter without protection. The moss will likely turn brown during the winter but will burst back to life once warmer temperatures and spring rain hit.

Potted Irish moss can remain outdoors during the winter but the containers will need some sort of winterization, such as a silo around them, mulch atop them, or a protective wrap that will prevent cold damage.

Common Pests

Irish moss is a relatively pest- and disease-free plant, which is one reason why it's so popular. It can, however, be attractive to slugs. To treat this issue, you can look into an organic slug bait, which can be applied annually to eradicate your pest issue. Likewise, you may find that moles wander beneath the moss and lift it as they bore underground. Be sure to pat the moss back down against the soil to prevent it from dying.