Irish moss, Sagina subulata, is sometimes called Scotch moss. Cold hardy in USDA Zones 3 to 9, the evergreen perennial is easy to grow and spreads quickly. It thrives in full to partial sun and enjoys moist, well draining soil. Add Irish moss to any spot that needs a mat of ground cover. It's perfect for low borders or small or limited areas such as between stepping stones, spaces that are often impossible to fill in. Irish moss will also thrive in rocky areas, where little else will grow. Although it becomes a little ratty looking during the heat of the summer, Irish moss typically revives when the weather begins to cool.
Space Irish moss plants in full or light partial shade with about six inches between each in early spring or fall. They should receive at least four to six hours of full sun daily, and the planting area should provide good drainage.
Water enough to evenly moisten the soil, but not so much that it's soggy. These plants hate wet feet. Keep the planting areas evenly moist throughout the growing season.
Apply a thin layer of mulch around the plants, if desired, but don't cover them with it.
Pinch off any yellowing leaves as they may occur throughout the season.
Divide existing clumps in early spring or fall if you'd like to add some Irish moss to other locations. Dig or gently but firmly pull up part of the clump and tear the desired amount off with your fingers. Transplant divisions immediately and keep them evenly moist.