By: Sandy Feather ©2006
Penn State Extension
Q. What do you recommend to control moss in a lawn? I have used a product called Scott's Moss Control and have applied limestone with little or no success.
A. Moss can be difficult to control. It is important to find and correct the underlying factors that have created such a favorable environment for the moss or else it will grow back quickly, as you have found. Correcting those problems will allow the grass to outcompete the moss.
Start by having your soil tested. Test kits available from your county extension office come with instructions for taking a good representative sample. Do separate tests for lawns, flowerbeds and/or vegetable gardens. If you have lawn areas that are very different -- one heavily shaded by mature trees vs. an open lawn in full sun -- have them tested separately. The results should come back in 10 to 14 days and will tell you exactly how much limestone and fertilizer to apply to correct the soil pH and improve soil fertility. To order a kit from the Penn State Extension of Allegheny County, see the end of this column.
Soil Test Results
If the area stays constantly moist, it will be very difficult to get ahead of the moss. You may need to install French drains to move water away from the area, redirect downspouts or take other steps to improve drainage. If improving drainage requires re-grading the area, be very careful around existing trees. A few inches of additional soil over a tree's root system can cause it to decline and may kill it completely. Roots cannot get sufficient oxygen if they are buried under too much soil.
If the area stays moist because of dense shade from mature trees, consider hiring a certified arborist to remove some of the lower limbs and thin dense canopies. Allowing more sun exposure and increasing air circulation will help the area dry faster after rainfall. Also, more sun will create a better environment for grass to grow. Even shade-tolerant varieties do best with some sun.
You can alleviate mild soil compaction with core aeration prior to applying limestone and fertilizer as recommended by your soil test. A core aerator is a machine that pulls out plugs of soil 3 to 4 inches long. The holes left behind promote better soil aerification.
Better soil aerification creates a more favorable environment for the development of a strong root system for the grass. Also, some of the limestone and fertilizer will filter down into those holes, affecting the change in soil pH and fertility where the grass roots live.
Finally, the species of turfgrass is important because most do not perform well in shade. Fine fescues do well in shady, well-drained areas. Rough bluegrass (Poa trivialis) tolerates shady, moist areas. Be aware that rough bluegrass has a floppy growth habit and is not the most attractive lawn grass. But it will grow where no other grass species will survive. Neither species will survive long term in extremely dense shade or constantly saturated soil.
Once you have addressed the underlying causes that permitted the moss to get the upper hand, then you can use a product registered to eliminate moss. Scott's Moss Control, DeMoss from Mycogen Corp. and LESCO Moss and Algae Eraser are chemical controls registered in Pennsylvania to eliminate moss. Be sure to read and follow label directions. If used improperly, both products can "burn" desirable turfgrasses.
You might also consider taking the path of least resistance and create a moss garden in your back yard. You obviously have ideal conditions for moss to grow. You can purchase different types of moss at garden centers and through mail-order catalogs. A woodland garden planted with native wildflowers, mosses and woody plants such as mountain laurel and rhododendrons may be more appropriate for the conditions in your yard than turfgrass. It is usually easier and cheaper to choose plants that fit your site than it is to change the site to fit certain plants.