Moss in the lawn is green flag to a problem
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Q: My lawn's full of moss. What's the best way to get rid of it?
A: After this damp winter, when temperatures generally stayed above freezing, mosses show up as one of the dominant plants in a lot of landscapes. The cool, wet months of fall and winter provide perfect growing conditions for mosses in lawns, under trees, and on hard surfaces such as decks and sidewalks.
Mosses possess unusual beauty, especially now when thriving after winter. Coexisting with them is often easier than fighting them (after all, we are in their territory).
When it appears in lawns, moss is a symptom of other troubles. Mosses erupt where the lawn dies out. Where you see moss in a lawn, suspect other problems such as too much shade or too much moisture. (Moss will move into lawns even in sunny areas when the lawn doesn't fight back.)
If you can't correct the shade or drainage, consider using a ground cover other than lawn, because the problems will simply continue.
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Logic would dictate simply dumping a discouraging chemical on the moss and getting rid of it. However, chemical control is only part of the solution, and not the first part
The best management for moss is growing a strong, well-maintained lawn. Lawn renovation and repair can be accomplished during March and early April in Western Washington. Do it now because these activities don't work well on the dry, struggling lawns of summer. The lawn needs to be growing in order to endure repair! (None of these steps is mandatory, but taken together they do help with a higher level of grass quality.)
First, check for thatch, an accumulation of roots and dead grass stems with live crowns of grass in it. Thatch prevents water penetration during dry spells and keeps the grass from growing well. Cut out a plug of turf, including the roots, and look at the soil surface/crown area. If your turf has more than 1/2 inch of thatch, take it out.
A power tool for de-thatching will make this job go much faster. It's not easy work. The result will be piles of brown, stiff root and stem pieces, and lots of moss lying loose on the ground. Thatching does loosen and pull out moss. Rake up the surface mess and compost it.
If the turf drains poorly or the soil is very compacted, you'll want to aerate after thatching. Soil cores resembling tiny cigars are pulled out of the turf mechanically, causing improved growth because more water and oxygen can reach the roots.
After these two steps, you'll have lots of scuffed bare spots, and perhaps relatively little moss. (Thatching is estimated to remove about 75 percent of moss infestation.) The lawn now needs overseeding to get strong new grass growing.
Choose a grass type suited to our area, such as a perennial ryegrass or turf-type fescue. (You will also find mixtures of seeds labeled for this area.) The package will indicate how many pounds to apply for a new lawn. When overseeding an old lawn, use half the recommended rate. Once the new grasses sprout, they will fill in and help with weed and moss resistance. If you do seed the lawn now, plan to water it during the summer to help with root establishment.
What if, after the thatching, a lot of moss remains? Consider treating it with chemical control before overseeding. Many lawn moss-control products are compounded with fertilizers, which tend to improve lawn color. However, you will have to rake out the dead moss afterward.
Iron compounds blacken moss; the moss controls with cryptocidal soaps turn the moss a sickly cream-white. Neither of these colors contributes to the beauty of the lawn. (Iron will stain concrete and stone, so apply it carefully. Cryptocidal soaps wash off without staining.)
Turf grasses love prairie conditions. Western Washington occupies a former forest land, home of mosses. You can expect to see moss return with next winter's rains. For more turf information, click on Washington State University's Puyallup Turfgrass Science Web site: www.puyallup.wsu.edu/turf
Mary Robson is area horticulture agent for Washington State University/King County Cooperative Extension.