Garden Myth: Lime to Control Moss

Moss growing in a shady lawn. Photo: pnwhandbooks.org

There is nothing worse than a garden myth that refuses to die, especially when it leads to gardeners wasting their money. And that’s the case with the stubbornly held belief that you can eliminate moss from a lawn or garden simply by applying lime. Unfortunately, even some garden centers repeat this false information, with the result that their customers invest their money uselessly. No, lime will not kill moss: applying it to do so is just throwing your money out the window! And it may even kill your lawn or garden!

This myth derives from the belief that moss only grows in acid soil and therefore, if there is moss in your lawn or garden, the soil must be acidic. And lime, being strongly alkaline, neutralizes acidity. But in fact, mosses are highly adaptable plants that will grow in acid, neutral and even alkaline soils. What the presence of moss really does tell you is that the soil is of poor quality, period. When other plants grow poorly, moss, being highly adaptable, moves in, occupying the empty space. The moss itself is not the problem, it’s a symptom of poor growing conditions.

When you see moss in your lawn, your flowerbed or vegetable garden, five factors may be involved:

1. Deep shade;
2. Mineral-poor soil;
3. Soggy soil;
4. Densely compacted soil;
5. Highly acidic soil (pH less than 5.5).

In fact, it’s usually a combination of these factors that so hampers the growth of other plants that moss is able to move in. Maybe the soil is compacted and shaded, or poor, soggy and acidic.

Some of these factors are easy enough to judge for yourself. You can easily see whether the location is shady and if the soil squelches when you walk on it, you can be sure the soil is soggy. Try to push a pencil into it: if that is hard or impossible to do, you can be pretty sure it is too compact.

There really is no easy way, however, to spot acid soil or mineral-poor soil at a glance. For that, you need to carry out a soil test. In particular, never apply lime before making sure that the soil really is suffering from excessive acidity. Lime is toxic to plants if misused!

How to Truly Eliminate Moss

The only real secret to controlling moss is to make sure the conditions are better for other plants. Aerate the soil if it is too compact (you can mix in lots of organic matter), drain it if it is soggy (perhaps by adding a raised bed), enrich it with compost or organic fertilizer if it is poor, thin out overhanging branches if it is too shaded and, of course, don’t hesitate to add lime if the soil test does indicate that the soil is very acid. Once that is done, other plants will be able to prosper and they will slowly, over time, take over and chase the moss out (moss doesn’t tolerate competition).

This isn’t going quickly enough for you? After making necessary changes, simply mulch the soil of your flowerbeds or vegetable garden. Mulch will cover the moss and cut off its source of light … and without light, it will die.

Moss in Lawns

You can’t mulch a lawn as you would a flowerbed, since mulch will cut off the light to the grass and kill it too. Instead, try the following:

First, fix the growing conditions. If not, all your efforts will be in vain.

Now, spray the area with one of the various anti-moss products (prefer an organic soap such as Safer’s De-Moss, widely available in garden centers) to kill the moss initially. Then rake it off and sow the area with grass seed. Try to use grass seed adapted to your conditions (there are mixes for partial shade, for example, if shade is part of the problem). If you don’t, the grass seed won’t take hold and, if there is nothing else there to take its place, the moss will return.

Why Eliminate the Moss at All?

Personally, I think this is the real question to ask. What is so wrong in having moss in your landscape?

Unless you live in a rainforest where the extreme and constant humidity can allow moss to grow up and over lower-growing plants, smothering them, moss usually hugs the ground and is not harmful to other plants. Instead its role is to “fill in the blanks,” growing where other plants won’t.

In fact, moss is even beneficial. It is essentially a living, self-maintaining mulch, growing naturally as an understory in forested areas, creating a moss layer that moderates abrupt temperature changes to the roots below, helping to keep the soil from drying out too deeply, contributing to enriching the soil and reducing weed growth. It can even form a beautiful green carpet quite as beautiful as any grass lawn. And moss between paving stones? How beautiful is that!

Of course, when the moss grows on man-made structures (roofs, wall shingles, etc.), you do need to control it as it reduces their useful life, but in a garden or in a lawn … why not learn to appreciate the beauty of moss and its benefits rather than seek to eliminate it?

Too often human beings think they know better than Mother Nature … but in my opinion, she is almost always right!

Here’s a blog on how to grow moss rather than eliminate it.

Article adapted from one published on January 15, 2016.