Irish moss, sometimes known as Scotch moss, isn't actually a moss at all. The perennial mat is seaweed that has tiny lime green leaves and blooms with little white flowers in the spring and summer. The most common use for Irish moss is a ground cover or filler in rock gardens or in the spaces between pavers. Irish moss is easy to grow and care for and is surprisingly useful. Properly prepared, the seaweed is used for tea, as a gelling agent in many foods and as a softening agent in some skin lotions.
Cultivate the soil for Irish moss by digging down an inch or two and then mixing in sand and compost to make the soil drain well. Choose a location that has full sun to partial afternoon shade.
Plant seeds on top of the soil one inch apart, or two inches apart for the spreading variety. Cover the seeds with a light coating of sand, making sure you can't see the seeds. Water carefully, so as not to float the seeds all into one place. You can plant the seeds in the spring after the threat of frost is gone or in the fall. Fall planting may result in birds or other animals eating the seeds during the winter, however, so it is best to plant in the spring.
You can also start the seeds indoors about six weeks before your last frost date. You can plant them in the same manner and transplant the seedlings outdoors right after the last frost.
Water to keep the plants damp but not soaked. Water once a week if that is enough to keep the soil moist. If it becomes very hot and dry, you may need to water as much as every other day. Because the roots are not very deep, long waterings are not necessary.
Use a water-soluble plant food that can be watered on once a month. Because the plant is thick, you will not be able to get a granular feed to the soil, and it may burn the tiny plants.
Plant another plant near the Irish moss that attracts ladybugs, such as dill, dandelion or coriander. Aphids have been known to be an occasional problem to the Irish moss, and the ladybugs will eat the aphids. This way, you will not have to use a pesticide on your plants.