Of two different prostrate plants of similar appearance, Sagina Subulata is the more common. The other is Arenaria Verna, usually called A.V. Caespitosa (Moss Sandwort). Both of these European natives make dense, compact, moss-like masses of slender leaves on slender stems. But Arenaria Verna has tiny white flowers in few-flowered clusters, while Sagina Subulata bears flowers singly and differs in other details.
Irish Moss vs Scottish Moss
What is the difference between these two plants? Green forms of the two plants are called Irish moss, and golden green forms (A.V. Aurea and S.S. Aurea) are called Scotch moss.
Use as Ground Covers
Both Sagina and Arenaria are grown primarily as ground covers for limited areas. They're also useful for filling gaps between paving blocks, however they won't grow well under conditions that suit true mosses.
How to Plant and Care for Irish and Scottish Moss
They need good soil, good drainage, and occasional feeding with controlled-release fertilizer. They take some foot traffic and tend to hump up over time. This can be controlled by occasionally cutting out narrow strips, then pressing or rolling lightly. Set out plants 6 inches apart for fast cover. Irish and Scottish Moss can tend to 'melt away' during long stretches of hot, humid weather.
Pests to Avoid
Control snails, slugs, and cutworms.
White flowers bloom in Summer through green foilage.