Sandworts in Brief
There are a number of Arenaria species, but only a few are commonly used as landscaping plants, and there is one that's considered a weed. Sandwort is a common name for minuartia, as well, but those are obscure arctic plants that aren't commonly grown by gardeners.
Growing six inches tall and spreading about 12 inches wide, mountain sandwort (Arenaria montana) bears one-inch white blossoms that cover the plants throughout the spring season. It has tiny elliptical leaves and is suitable for USDA zones 4 to 7.
Mountain sandwort is used mainly in rock gardens as a small scale groundcover or as edging materials along pathways. If you can't find mountain sandwort in your local nursery, Outside Pride is a good source for ordering seeds online.
This is another type of sandwort that is sometimes referred to as Scotch moss (Arenaria verna). This species is a mat-forming groundcover, growing just two to four inches high. It has tiny white flowers in summer, but is largely grown as a foliage plant for its miniscule, moss-like leaves. Grow it easily in USDA zones 4 to 9.
Irish moss tolerates some foot traffic and can be used as a small scale lawn substitute or to fill the spaces between stepping stones. It's also useful in pots and hanging baskets around upright plants.
This species is common in nurseries, especially the form 'Aurea', which has golden yellow foliage.
Corsican sandwort (Arenaria balearica) closely resembles Irish moss, except the flowers are slightly larger and held a couple inches above the foliage. Try Sandy's Plants for ordering this species online. It's hardy in USDA zones 4 to 11.
Thymeleaf sandwort (Arenaria serpyllifolia) is an annual species that is considered a weed. It resembles the other Aernarias, but the flowers are smaller and fewer and the leaves are larger. It is easily pulled by hand or removed with a garden hoe if you should happen to find it in your garden.
Sandworts like full sun and well-drained soil. Their shallow roots make the prone to drying out, so they may need water several times each week in hot weather. They are adaptable to various soil types, but prefer loose garden soil that has been amended with compost.
Care and Maintenance
Sandworts are virtually immune to pests and disease and require very little care besides watering.
The one other maintenance activity is to trim off the spent flowers after they fade in early summer. Giving the foliage a slight trim in early fall will keep the plants looking lush the following year. Where it is used as a groundcover it is feasible to use a lawnmower to trim sandwort.
A Splash of Green
Sandworts are covered in white flowers for part of the year, but they are even more celebrated for their tidy appearance as an evergreen groundcover or accent plant. They create a lush carpet of green that looks soft and inviting, which lasts through the winter months in mild climates.