Irish Moss

Family: Caryophyllaceae (Pink family)
Genus: Sagina
Species: subulata

In my garden, I sometimes have trouble leaving well enough alone. There are many moments when I envy those who put in their plants, achieve the look they’re after, and head for the lawn chair to read a good book.

My lawn chair stays empty and I’m behind in my reading. I spend my time rearranging, replacing, and re-doing. Some of this happens because of poor planning, but much of it comes from what my spouse calls a quirky desire to do something different.

Alas, I fear my garden will always be a work-in-progress. This year, I was unhappy with the inability of creeping thyme (Thymus praecox) to creep far enough in two years to fill in the spaces between the large stones in one area of my yard. The thyme spread more quickly over the rocks than it did around them. The soil might have been too damp and the thyme might have been sun-deprived. But I didn’t give it a chance to explain. Instead, I tore most of it out and looked for an interesting replacement. It would have been sensible to opt for blue star creeper (Pratia pedunculata, sometimes sold as Laurentia fluviatilis), a very dependable performer in our area. But “sensible” is not always my first choice when I’m gardening. I tend to take calculated risks and try new things. Blue star creeper was already established in another area of the yard. I wanted something different.

I like the clumpy look of Irish moss—it reminds me of the rolling green hills in the Emerald Isle—and I was attracted to the sprinkling of small white flowers I spotted in a patch planted curbside in a parking strip on South Hill. So Sagina subulata it would be for me.

Sagina subulata and Sagina subulata ‘Aurea’—Irish moss and Scotch moss, respectively, with the former deep green and the latter, chartreuse—are not true mosses. They are perennial plants, grown primarily for their foliage. They have a soft, lush feel and appearance, and they will take light foot traffic when placed—as my Irish moss is now—between stepping-stones. They hail from northern Europe and are hardy to 30 degrees below zero. The British Natural History Museum lists S. subulata as native to Scotland where it is known in English as Heath Pearlwort and in Gaelic as Mungan Mòintich.

S. subulata was one of the first plants to be named—by Antoine-Laurent De Jussieu—in the modern system of plant nomenclature. Sagina in Latin means “fattening,” attesting to the fact that sheep prospered in fields where the plants flourished. I suspect that has more to do with favorable growing conditions for forage crops—marked by the presence of Sagina subulata—than it does with the nutritional value of Irish moss. Subulata tells us that the leaves are “awl-shaped”—that is, they are slender, cylindrical, and taper to a point. The small white flowers are borne singly, from mid-spring to early summer. A similar plant—Arenaria verna—has flowers in clusters but is otherwise nearly identical in appearance and is also known as “Irish moss.” There is yet another growing thing called “Irish moss,” but it is a red seaweed with the official moniker of Chrondrus crispus. That kind of Irish moss is the source of carrageenan, a natural jelling agent that is added to edible products from bottled salad dressing to toothpaste.

But you won’t find seaweed in my back yard. Far from being true moss or red algae, the Irish moss I’ve planted is a member of the large Caryophyllaceae family. It is related to Lychnis (rose campion and Maltese cross), Dianthus (carnations and sweet William), Saponaria (soapwort), and Gypsophila (baby’s breath). Common chickweed is a member of the same family.

Because all these members of the Caryophyllaceae clan thrive in my garden—need I mention chickweed again?—I can posit that Irish moss will do well, too. I read that Sagina subulata dislikes hot summers—no problem there! I’m told that even it if does brown out, it will green up again in cool fall weather. It is bothered by slugs, evidently, so I’ll watch out for them, liquid slug-death and salt shaker at the ready. I’ve planted my S. subulata deeply in soil that is rich with organic material, and I’ve added some time-release fertilizer, which I’ll replenish next spring. The small plugs are placed six inches apart where they will receive direct sun into the afternoon—enough for Irish moss, perhaps, if not for creeping thyme. I know Irish moss demands moisture, so I’ll use the gray water from our household. In short, I’ve followed directions and now I’ll hope for the best.

In the event my Irish moss bites the dust—suddenly and completely, as some here have seen theirs do—I’ll probably go back to the tried-and-true blue star creeper. If I must have Irish moss around, I’ve just learned that it can be used as a living liner for hanging baskets, an alternative to coco fiber or sphagnum moss. Something different, a new “look”—that’s what my gardening is all about.