Whether you live on the wet or dry side of Oregon's Cascade Mountains, moss can infest your lawn. To discourage its growth, Rob Golembiewski, the turfgrass specialist with the Oregon State University Extension Service, suggests asking yourself the following questions:
* Does your lawn have a poor diet?
Your lawn most likely lacks fertilizer. Moss tends to grow where grass stands are thin and malnourished. But properly timed applications of nitrogen will increase the turf's density, vigor and competitiveness. Fall and spring are the best times to apply it.
* Does your lawn get enough sun?
Grasses grow poorly in dense shade. But if you're in Central and Eastern Oregon, try planting fine fescues, which do well in dry shade. In Western Oregon's wet, shady sites, roughstalk bluegrass and bentgrass persist better than other grasses. Or consider removing shaded mossy lawn altogether and planting shade-loving, native perennials and shrubs.
* Is your lawn in a naturally soggy area?
Moss thrives in damp wet soils, which often are caused by poor drainage or excessive irrigation. Poor drainage sometimes can be improved by changing grading, aerating lawns, removing thatch, or installing subsurface drain lines to lower the water table.
* Do you water your lawn too much?
Avoid watering at night, particularly in fall or early spring when moss growth is vigorous.
* Is your lawn "injured" by the activities of children, insect pests, pets or vehicles?
Baseball games, bikes, dogs and crane fly larvae can physically injure lawns and contribute to moss encroachment.
* Are you stingy with the water in the summer?
Just like too much water, too little water can encourage moss. Lawns that are not irrigated turn brown and thin out during summer. When fall rains return, moss may grow in faster than the grass.
* Is dethatching a good idea?
All in all, the best way to discourage moss in lawns is to encourage good growing conditions for your grass. Golembiewski recommends dethatching your lawn between April and early June with a mechanical dethatcher, available at rental outlets. Dethatching will remove about 75 percent of the moss.
* Do you need to seed or fertilize?
After dethatching, seed thin areas, and fertilize the entire lawn at a rate of one to two pounds of nitrogen per 1,000 square feet to stimulate growth of grass, preferably between April and early June. Follow up in the fall with more fertilizer to reduce the problem for the following spring.
* What are the chemical methods to control moss?
Iron compounds are highly effective and work quickly to stimulate a "green-up" of turf. Complete fertilizers with iron remove moss while stimulating grass growth. A drawback to iron is that it stains concrete and many other surfaces; it must be applied carefully. Follow label instructions.
"The key to effective control with iron compounds is thorough coverage of moss foliage," Golembiewski said. "Liquid materials are very effective and give almost instant results. Smaller particle-sized fertilizer-plus-iron products are more effective than larger-sized granular products because they provide better coverage of the moss."
* Can you get rid of moss that's been around for a few years?
In older lawns that have heavy, established moss problems, you must be more aggressive, Golembiewski advised. "Moss doesn't decompose quickly like treated weeds do," he said. "As a matter of fact, moss seldom dies completely. Treated moss is merely in a dehydrated state. If any green moss still exists two to four weeks after the first treatment, a second application will be required."
An alternative product is "cryptocidal," a moss-killing soap. It kills on contact and tends to bleach moss to a whitish yellow, rather than the dark brown color of moss treated with iron. The soaps are safe on sidewalks and other structures. Follow instructions on the label.