Installing an Emerald Carpet: Thank you, Irish Moss

Lots of plants have a “carpeting” growth habit. But Irish Moss grows into such a dense and cushioned carpet, it seems to beckon us to run our hands through it.

Irish Moss is in the same family as much-loved carnations and pinks. But while these other family members grow into fairly compact mounds, Irish Moss spreads a bit. This plant known as Sagina subulata will not exceed a height of an inch or two, but it can spread to around one foot. And when it does, its fluffy emerald growth is hard not to touch, and impossible not to admire.

When gardeners shop for Irish Moss, they also tend to come across Scotch Moss, which is very similar. But the Irish cousin is the spreader, and the plant you want if you aim to fill an area with low and cushiony greenery. With both of these plants working well together, some gardeners use the two in patchwork displays that show off slightly different hues, with Irish Moss being emerald and Scotch Moss being chartreuse.

Now, for me, Irish Moss comes to mind at this time of year for several reasons: At the time of holiday egg hunts, Irish Moss, or Sagina subulata, provides the perfect base upon which to place a special treat or two. And shortly after the earliest spring holidays, Sagina subulata will begin to show off tiny white flowers, five petals each and beautiful in their simplicity. Furthermore, this is also the time when this strong little “carpet” can travel without issue: This plant is prone to overheating in transit, so this is the right (cooler) time to order up a few greenhouse trays, get them shipped, and get them dug in before flowers emerge.

When choosing a spot for Sagina subulata, make sure there is enough sun to keep this plant looking its best. It can handle some shade, but it does crave light. And when planting, note that Sagina subulata appreciates some amount of richness to the soil it is in. While some carpeting plants seem to spread well in very “thin” soil, Sagina subulata does better in soil that is slightly more nutrient-rich.

Once you find the right location, expect Irish Moss to go about its work of looking healthy and green, even under occasional foot traffic. It is perfect near the garden path, draping slightly over rocks, or as an underplanting in some areas. 

Now I hesitate to tell sad tales, but when I moved into my home, I inherited an elevated and very visible garden bed with creeping phlox that apparently had done well for years. But I like to think that the phlox was close to the end of its lifespan, as it slowly faded. (I hate to think that I was responsible for its demise.) First it failed to flower. Then it dried and slowly died back over the couple of years that followed. When I finally dug it out, I spent one summer pulling weeds from fine mulch I had put in its place. And then came the brainstorm of covering the same area with Irish Moss. I began to feel less bad about losing the phlox. Things started “looking up” when my green carpet made its appearance.

Starting with weed-free soil, Irish Moss will not let new weeds creep in, for the most part. Able to do well in Zones 4-9, this herbaceous perennial is a workhorse.

Plant full clumps of Irish Moss to fill larger areas, and then pull apart a clump or two to cover smaller spots. This is a plant that can be divided easily, with just a little tugging and teasing apart of the roots.

A carpet of perennial greenery… yup, that’s spring (and summer, and fall). Irish Moss. Sagina subulata. Glad I found it.