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Some moss-lovers advocate just accepting its existence. Acknowledge that these are intriguing and often beautiful plant forms. Mosses cloak the north sides of trees with green banners, and add to the interest of winter walks in the woods. Local gardens, such as Bloedel Reserve on Bainbridge Island, have created display gardens entirely carpeted with moss. George Schenk, garden writer, devoted a book to moss, (Moss Gardening, Including Lichens, Liverworts and other Miniatures, Timber Press, 1997.)
When mosses can become enemies of gardeners when they colonize spots that we'd prefer to see filled with something else. Moss can be annoying in lawns and is downright hazardous when it flourishes on walking surfaces like decks and sidewalks. Too much moss on a roof can affect the integrity of wood shingles.
Lawns develop moss problems when bare spots give the moss somewhere to grow. Think of moss in the lawn as an indication that the turf is stressed by one or more common problems. Too much shade, poor drainage, low fertility, soil compaction, or thin spots where turf has died out all contribute to difficulties. Any one of these, or quite often a combination of these conditions, will generally be present where moss is a problem. Early October is an ideal time of year to renovate lawns and correct the problems leading to moss infestation.
Moss is a symptom of lawn problems, not a cause of them. Mosses are distinctly different plants from turfgrasses. Though they are both green, the resemblance stops at that point.
A true moss has root-like stem extensions underground. These are shallow and almost feather-like, not roots as gardeners recognize roots. Mosses do not have veins, or the vascular system that supports grasses. They do not retrieve water from soil and send it along veins out to leaves. Mosses can and do survive in distinctly different conditions than grasses. They don't make food through photosynthesis as grasses do.
The obvious place to begin with a moss management program in turf is to make sure that the turfgrasses have the best possible conditions for growth. Lawns need good light. They also need fertile, well-drained soil to support roots that can penetrate 6 to 8 inches down, or even deeper.
Start your moss control program by giving the lawn good, thorough basic care, beginning with a clear analysis of the location and how the lawn is established. Be sure to apply the late fall fertilizer in late November, using a 3-1-2 formula in a slow-release type fertilizer. Using a low percentage of nitrogen (the 3 number) in a slow-release form will help prevent large quantities of fertilizer from washing into surface water and causing potential pollution of fish populations in streams, rivers, and Puget Sound.
What about the soil conditions? Poor drainage means that the area around the grass roots stays soggy and wet. Turf requires water, but needs good drainage for root health. Any place in a lawn where water stands after rain or irrigation, or places where the ground is too compacted to drain well will be potential trouble spots for moss and weeds.
Sometimes lawns are installed over ground that's been compacted by heavy equipment, such as around a newly-constructed home. In many locations in western Washington, drainage is restricted by layers of hardpan, which is often nearly impermeable to water. A lawn planted over compacted soil or hardpan will never grow well, and cannot become thick enough to resist moss and weed invasions. Analyzing the problems may result in choosing to install drainage systems or drilling through the hardpan.
In these extreme situations, there are no easy fixes. Get a qualified turf professional to help determine what needs to be done.
If you are undertaking lawn renovation to remove moss and repair the resulting gaps in the turf, get rid of the moss first. Established moss can be removed by hand raking, though this method doesn't control moss effectively. A lot of rhizomes and spores will be left behind to regrow. If the moss is raked out but nothing else is changed in the turf situation, the moss will return almost immediately when weather conditions allow.
Correct the lawn problems in addition to reaching for the moss control chemicals.
Several common chemical compounds registered for moss control. Most of these contain iron, in the form of ferrous sulfate, ferrous ammonium sulfate, or iron chelates. These iron-containing products are sold both in granular and liquid forms. The finer the particles, the better the coverage and the better the moss control.
The moss will blacken with an iron application. Follow label directions carefully. Products containing iron will stain concrete and should be kept off sidewalks and patios.
Another type of moss control product contains potassium salts of fatty acids, essentially a soap-type compound. These cause mosses to yellow and brown out, not turn black. Some yellowing and discoloration of the turf as well as the moss will occur. These soap-type products are more commonly used to remove mosses and algae from hard surfaces in the landscape than they are for applying to moss infestations in turf.
Again, read the label to determine the best site of application and method of handling. Any surface that's covered with moss and also used for walking needs to be managed to control the pest, because it can present a significant winter hazard in landscapes. Apply the moss control and be sure to brush or scrub the walking surfaces after the moss dies. Follow directions carefully, reading the label thoroughly.
Hortsense: Managing plant problems with Integrated Pest Management
