How to Grow Irish or Scotch Moss (Sagina Subulata). Though not a true moss, Irish moss (sometimes called Scotch moss) forms a tight mound like moss does, and it works well as a ground cover around stepping-stones and in rockeries. Irish moss thrives in USDA zones 6 to 9. By jamiemazdain Gardening Tipswith gardeninggrowirishmosssaginascotchsubulatatips