Irish moss, or Sagina subulata, is often referred to as Scottish moss or sandwort. This sturdy, versatile perennial ground cover spreads rapidly to produce a soft, lush carpet of bright emerald green. Irish moss adorns its lance-shaped leaves with tiny white summer blooms. It also serves well as an attractive addition to the pond or rock garden and is commonly used to fill gaps between flagstones and in dry walls. Irish moss is typically available from local plant retailers and home improvement centers in time for spring planting.
Choose a very well-draining location in full sun or partial shade for your Irish moss plants after all danger of frost has passed for your area. Cultivate the soil to a depth of about six inches and work one or two inches of organic compost into it. Add an all-purpose fertilizer to the planting holes. Follow the packaging instructions carefully. Plant Irish moss at the same level it occupied in the growing container and space plants about six inches apart.
Apply about an inch of organic compost to your planting site. This will serve to retain moisture for the plants and discourage weed development.
Water the planting site slowly and thoroughly. The area should remain evenly moist but not wet or soggy throughout the first season after planting. This will ensure that your Irish moss becomes well established. While these plants don't like wet feet, it's important that you don't allow the youngsters to dry out. Foliage will turn brown and dead spots will develop as a result of excessively dry growing conditions.
Weed your Irish moss plants often and aggressively. You need to get rid of weeds before they grow tall enough to begin poking up into the thick carpet and become entangled in it. Weeds will be much more difficult to remove if that occurs.
Feed the Irish moss liquid fish emulsion in April. Repeat the application in late June or early July when the plants have finished blooming for the season. Follow the manufacturer's recommendations carefully.
Do your best to protect your Irish moss by discouraging people and pets from treading on it. The thick, low-growing carpet appears soft and cushion-like, seeming to nearly beg for foot traffic. The truth is that these plants won't respond well to being trampled.