Growing Concerns: Gardener can patch bare spots in Irish moss

Q: I am trying to grow a bank of Irish moss in my back yard. I have been doing this for about 10 years. This year I notice that I am getting some bare spots or worn spots. There is no foot traffic, so I was wondering what I could do to preserve this beautiful bank of Irish moss. Thank you very much for your help. – Merry Staser

A: Irish moss, Sagina subulata, is one of my favorite ground covers, and I’ve been growing it for decades. Despite its common name, it isn’t really a moss, but a very low-growing, spreading perennial plant that, in the best of conditions, carpets the garden in emerald-green velvet. Its cushiony softness invites touching, and in late spring and early summer, tiny, white, star-like flowers add to its beauty. Its sibling, Scotch moss, has the same characteristics, but is golden-green in color.

Sagina thrives in a sunny or partly sunny location in well-draining soil with adequate moisture. It doesn’t like wet feet, but will develop dead, brown areas if allowed to dry out. Moderation is the key. When preparing to plant, work some compost into the soil, along with time-release fertilizer. I feed my Irish and Scotch moss well-diluted liquid fertilizer (fish emulsion works well) around April, and then again after it has finished blooming in late June or early July.

Sagina doesn’t take well to direct foot traffic, so don’t do any jigs on your Irish moss. It looks wonderful surrounding stepping stones and ponds, though, and is a natural in rock gardens and Asian-style landscapes.

Although it forms a tight carpet, it is not impervious to weeds and grasses. Check it regularly for weed seedlings and remove them immediately, because once they take hold, it’s difficult to remove weeds without harming the moss.

Although semi-evergreen in our climate, Irish and Scotch moss will occasionally freeze back during extended periods of frost. Likewise, it dislikes hot, dry conditions, which can lead to brown patches and bare spots. Other possible causes of patching include garden chemical overspray, dog or cat urine, over-fertilization, or inconsistent watering.

I’ve read that slugs will occasionally make a meal of Sagina. I haven’t personally observed that in my own garden, but I certainly wouldn’t discount it. Moles searching for insects beneath the mossy carpet may heave the roots out of the ground. These areas will eventually die out if not promptly tucked back into the soil.

Irish and Scotch moss propagate easily by division, and this may be the key to filling those bare spots in your moss bank, Merry. Here’s what I do: Fill a plastic nursery flat with clean potting soil. Using your fingers or a knife, break off small pieces of Sagina from your existing bank. Settle it into the soil in the nursery flat and water well. Place in an area that gets plenty of light (but not direct sun), and keep the flat from drying out. Within a few weeks, the moss should begin grow and spread.

As soon as the new growth looks strong and healthy, transplant pieces of it into your bank to fill in those bare spots. Keep the flat going, so you’ll always have some on hand to harvest. This method works well with other low-growing ground covers such as baby tears, Corsican mint and thyme.

Now here’s what not to do, Merry. I have a curving bed of Irish and Scotch moss (I like to combine the two) approximately four feet by four feet. Last winter, a few spots of moss froze out. In early spring, instead of filling in with more Sagina, I decided to try plugs of baby tears (Helxine soleirolii). Bad decision! The baby tears are now running rampant over the moss, and the two plants are impossible to segregate. By the end of summer, baby tears will have overtaken the moss bed entirely. My only option will be to dig out the entire bed, making sure that I remove every little shred of baby tears. Then I’ll have to start all over again with a fresh batch of moss. Duh!

By the way, Irish moss is not native to Ireland. Both Irish and Scotch moss’s ancestry is in Scotland. My guess is that Irish moss was named for its resemblance, in miniature, to the soft, rolling, green hills of the Emerald Isle. Another bit of horticultural trivia: “Irish moss” is also the common name for a red sea weed found in the North Atlantic Ocean. Go figure.

Mariana Graham writes this column as a volunteer WSU-Island County Master Gardener. Contact her at

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