Moss takes advantage of cool, wet winter

By Marianne C. Ophardt, Special to the HeraldMarch 19, 2011 

KENNEWICK - I have been receiving numerous inquiries from local gardeners about how to control the moss that's invading their lawns and gardens.

Most of us know that "a rolling stone gathers no moss," but that's all we know about this primitive green plant.

Moss reproduces by spores instead of seeds. Botanists consider moss to be lacking true roots, stems or flowers. They are an opportunistic plant that can be found growing in all parts of the world, in diverse environments where there's plenty of moisture available during at least part of the year.

Mosses can be found growing in or on rocks, roofs, concrete, forest floors, local lawns, as well as at the bottom of lakes, ponds and streams.

Because mosses lack true roots and vascular tissues, one might wonder how they get needed water and nutrients. Some types have rhizoids which are rootlike filaments that act as roots. Others types of moss absorb nutrients from free water on their leaves. Most mosses require very little, if any, soil to grow.

In the Northwest, it's not unusual to find moss growing in woodland areas and plaguing structures, lawns and gardens west of the Cascades.

It is surprising that moss can be a problem in our dry shrub-steppe area of Central Washington.

During the cool, moist periods of the year, moss thrives and grows and then becomes dormant during the hot, dry times of the year. We have just experienced a cool, "wet" fall, winter and early spring during which moss apparently has prospered.

Moss is opportunistic, not aggressive. Whenever moss becomes a problem in gardens or a lawn, gardeners should investigate why it's growing there. Moss tends to grow where the soil is very compacted, the drainage is poor, the soil stays very wet for periods of time, where it's shaded, or where the fertility is poor -- or a combination of these conditions. Acid soils also favor moss growth, but that's usually not a problem in our region.

In lawns, you can rake or power rake to remove the moss. There also are chemicals that can be applied to kill moss and not harm the grass. However, the real key to control is promoting healthy, vigorous turf with proper watering, adequate fertilization, and good aeration and drainage. Dense shade leads to thinning of lawn grass and also favors moss growth. If the shade is from trees and shrubs, consider having them thinned to allow more light or tolerate the moss.

In gardens, there are no chemicals for control of moss that won't harm other plants. Your best option in flower, vegetable and landscape beds is to scrape the moss off the soil surface using a hoe. Without real roots, it's only growing on the surface and is easy to remove. Correct any drainage or compaction problems.

Moss is not harmful to your lawn or garden, but it does indicate that there may be a drainage or soil compaction problem. If these conditions don't seem to be hampering the growth of your garden plants, you might even consider yourself lucky.

One current gardening trend is moss gardening. There's even a website (mossacres.com) where you can buy moss. I guess one gardener's "trash" is another's treasure.

In addition to mosses, area gardeners sometimes are bothered by a different low-growing primitive plant closely related to moss called liverwort. Liverwort has a branching flat and wavy ribbon-like body that grows along the soil and it favors the same conditions as moss and can be controlled in the same manner.

* Marianne C. Ophardt is a horticulturist for the Washington State University Benton County Extension.

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