Irish or Scotch moss (Sagina subulata) is not a true moss but a flowering plant with tiny, needlelike leaves and insignificant white flowers. It can grow in shade, just as mosses do, but will also take full sun. Irish moss is the common name for the ordinary green form. The greenish-gold form, S. subulata "Aurea," is often called Scotch moss. It is also called pearlwort.
Ease of Care
Irish moss is native from Iceland to Spain growing on dry, sandy or gravelly soils and needs no more care in cultivation than it gets in the wild. Of course, like all plants, it needs extra water the first few years to help it establish a good root system and it may look better with regular soakings in summer, depending on the dryness of your climate and how much sun it receives. Do not fertilize.
The only other maintenance needed could be cutting out portions that have mounded up, spoiling the smooth surface, or mowing the "Aurea" form to prevent seeds that might sprout as the green form.
Irish moss is rarely bothered by disease, though heavy soil or poor drainage may cause crown rot. If you have clay soil, plant on a slope for good drainage and improve the soil with organic matter.
Ease of Propagation
Irish moss can be easily grown from seed, an economical way to cover a large area. Sow the seed on a flat of potting soil in fall. Cut the flat into plugs several inches wide and transplant to their permanent position after the last frost in spring. You can also start new plants easily by pulling apart a clump.
A Lawn Substitute
Sagina can take some foot traffic without damage, though not as much as lawn grass. It is best used in small areas, where its smooth texture contrasts with the flowers and foliage of other plants. It can also be planted between stepping stones. Since it will grow well with more shade than lawn grass, it's often a better choice under trees and tall shrubs.
A Nurse Plant for a Moss Lawn
When Irish moss is grown in full shade, it is often invaded by the true mosses. You can take advantage of this trait to create a lawn of true moss by planting Irish moss and then allowing the true moss to take over. The Irish moss dislikes complete shade and will gradually die off.