Answer: Sagina subulata and Arenaria verna, Irish and Scotch Moss, are two different plants with similar appearance. Both make dense, compact, mosslike masses of slender leaves on slender stems. While both resemble moss, their growing requirements are quite different from the moist, shady conditions under which true mosses thrive. Both Irish and Scotch Moss produce tiny flowers which develop seeds. In fact, they can self-sow to the point where they become pests in the garden. Your plants should grow well in full sun to partial shade, with regular water. They require good soil and excellent drainage. The yellowing of your plants might indicate overly moist soil conditions and the development of a fungal disease. Dig out the affected plant parts and adjust your watering practices. Instead of keeping the soil constantly moist, allow it to dry out a bit between waterings. The plants are not heavy feeders and too much nitrogen will cause the foliage to grow into mounds rather than to create a low carpet. One fertilizer application in the spring and another in the late summer should keep your plants growing at just the right rate. In my garden I propagate Irish Moss by cutting 1"-2" strips from established plantings and replanting them. The empty spaces fill in rapidly and I think it helps to prevent overcrowding of the existing plants. Hope this information helps!
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