Careful planning keeps moss where it belongs: in gardens

In February, I had a chance to visit the Bloedel Reserve’s native woodland and meadow gardens on Bainbridge Island. Most everything was still dormant, except the mosses.

In the formal moss garden under the tall firs, the late winter light and a little rain turned something most people consider a nuisance into a beautifully rich, emerald green carpet. It made me wonder why we put so much effort into getting it out of our gardens.

Most people don’t see moss as a landscape element, only as a weed. The appearance of moss in a yard or garden is the symptom of a wide range of problems that are not easy to fix for the long term. We had a mild winter this year and the moss never really quit growing and got an early start.

Moss is likely to move in when one or more of the following conditions are present: areas of thin grass cover, worn lawn areas where animals and children play, shady areas, areas of compacted soil, soggy areas, drought stressed grass, grass cut too short, lack of fertilizer, poorly prepared lawn seed bed, poor lawn maintenance, acidic soil conditions and the wrong grass type.

Because most of these conditions come down to fertility, soil acidity and growing conditions, the first thing to do is to have your soil tested for nitrogen, phosphorus, potassium and pH. The Spokane Conservation District can run this test for $30, check out their website ( www.sccd.org) for directions on how to take a sample. The test will give you recommendations of how much fertilizer to add and how to alter your pH. Lawns prefer a pH of between six and seven.

With your test results in hand, you can begin planning your remediation program. Early spring and fall are the best times to go after moss. Moss can be treated with iron sulfate or ferrous ammonium sulfate. Both are sold under a variety of trade names. Once treated moss turns black, it can be raked out of the lawn. Next, aerate the lawn well to allow air into the soil and reduce compaction. If you need to raise the pH, add the amount of lime recommended by your soil test. Reseed any thin or worn areas with the proper seed. Bluegrass does well in sun; fescues like shade. Water the lawn properly; water less often and for a longer period to get water deep into the soil. This allows the roots to grow deep where they are more drought resistant.

If you have areas that stay wet, look at changing the drainage so the excess water flows away from the area. In shady areas, look for ways to prune trees to allow in more light. Mow lawns no shorter than three inches to maintain healthy turf. Fertilize the grass in April and September with a slow-release organic fertilizer that will give the grass what it needs but doesn’t overstimulate it. Really dark green turf is not healthy.