Irish moss is actually not a true moss, but rather the common term for two plants, Sagina subulata and Arenaria. Irish moss is also known as Scottish moss, and differs from the Irish moss seaweed, Chondrus crispus. For walking paths, lawns and rock gardens, look for the plant with a dark green color that grows approximately 1 inch high.
Use Irish moss between flagstone pavers, which will absorb the brunt of the foot traffic. Irish moss will break down if you subject it to heavy foot traffic and reduce your walkway to a mud path. Irish moss will never grow very high above the flagstones. The plant rarely lays perfectly flat, but grows in small mounds. To create a flatter appearance, cut out small sections and push down the remaining plant into the soil. The deep green color creates a striking contrast to lighter-colored flagstones. Keep the moss moist and it will grow to fill in all of the gaps.
Use Irish moss as a grass substitute for your lawn, but heed the precautions against using it in high-traffic areas. Similarly, if you do not use your lawn as a play area for children or pets, you will be able to create a grass-like area with this plant. Irish moss grows in areas where the soil is relatively shallow, and in places where grass is not able to extend its roots deep into the earth. A field of mature Irish moss resembles a lush green meadow. In the late spring and summer, it will sprout small white flowers. Start the moss from seed indoors or direct sow after the last frost. Plant seedlings at the same depth they were in their container. Water the plant frequently while it is establishing itself in the new location and keep it evenly moist thereafter.
Irish moss adds contrast and interest to a rock garden, and will not interfere with other plants growing in the garden. Allow the plant to grow on stones for a more natural presentation. If you prefer a more structured and tailored look to the space, trim the Irish moss if it begins to encroach on the stones. To give the plant more room, cut out sections and let it re-grow in the newly available space. Do not discard the parts of the plant you have cut out; instead, use those pieces to propagate the plant in other areas of your rock garden or elsewhere