Ground View

By Glen Andresen

You’ve got to hand it to moss, alright. These plants in the bryophyte family lack a vascular system to carry water or food; they get both through the air. They neither flower nor produce seeds, reproducing instead via spores. Some mosses can survive long periods of drought in a dehydrated condition, only to return to life within hours of hydration. They often are considered “lower” plants because they were among the first to evolve, yet here they are today, hundreds of millions of years later, still colonizing surfaces. Dozens of species of moss grow in the Pacific Northwest but we generally only take time to notice the ones that grow in lawns, patios, walkways and roofs.

Moss growth normally starts with fall rains and reaches a peak in early spring. Because most grasses grow poorly in winter, mosses are able to invade and dominate lawns in only a few months. Moss growth declines in summer as conditions become drier and turfgrass becomes more vigorous, but under shady, irrigated conditions moss can grow through summer.

Many gardeners consider moss in lawns to be a problem. But why? That’s a very, very good question. In my opinion, unless the lawn is serving some special purpose (such as backdrop for a photo shoot for some fancy pants magazine or a wedding), moss can be left alone, because it is what is best suited to that spot. You see, moss is a symptom of poor grass-growing conditions. And unless all of the conditions that contribute to moss growth are addressed, the moss will always return (just as it has for millions of years!).

The conditions that contribute to moss growth are poor drainage, high soil acidity (that is, low pH), too much shade, compacted soil, low soil fertility, and/or excess moisture. All of these conditions can be rectified if you want to put in the time and effort. For example, you can correct poor drainage by installing French drains; low pH by regular liming; compacted soil by core cultivation, slicing or thatch removal; too much shade by cutting down trees; low fertility by applying compost and organic fertilizer every year; and excess moisture by watering only when needed. As you can see, changing all of these conditions could be overwhelming, so the best solution in my book is just to tolerate or even encourage the moss. It’s the ol’ “if you can’t beat ‘em, join ‘em” defense! I personally employ the “freedom lawn” technique, which is to allow to live anything that survives below my lawn mower’s blades.

Often the best defense against moss is to have a healthy stand of grass and to follow some very simple guidelines. What could be simpler than these three suggestions? (1) Make sure whatever blade you are mowing with is sharp, (2) adjust the height of your mower so that you remove no more than one-third of the blades of grass in any single mowing, and (3) leave the grass clippings on the lawn whenever possible.

Maybe you don’t even need turf in certain areas. For example, for wet boggy places try Gaultheria shallon (salal); for steeper slopes Mahonia nervosa (dull Oregon grape); and for shady areas a good choice would be Mahonia repens (creeping Oregon grape). There are plenty of other native plants that might fit your tastes and area.

Finally, a word or two about chemical controls. At best these offer just temporary moss control in grass, because unless the underlying conditions are corrected, the moss will come back. Most commercial formulations contain metals such as iron, copper or zinc as the active ingredient. Zinc especially is toxic to aquatic animals and can pollute rivers and streams. Iron stains concrete and copper is naturally toxic to fungus, including those fungal species in the soil.

So the word from here is to have less lawn, don’t be afraid to manually rake the moss out of your lawn (you’ll even get some exercise in the process), or just enjoy it — especially when you are barefoot!

Glen Andresen hosts “The Dirtbag,” heard every second Monday at 10:30 a.m. on KBOO 90.7 FM. He tends his bees on a three-quarter acre organic garden at a retreat in Eagle Creek. He also coordinates Metro’s Natural Gardening Program. Comments and questions may be sent to glen (at) pacifier.com or c/o The Portland Alliance.