Extension Educator, Horticulture
If I were a leprechaun I would doze away the summer on a bed of moss. It looks so pillowy soft. I know not everyone shares my love of moss. I get many questions in the Extension office about how to kill it. People are concerned it may be killing off their grass or eating a hole in a tree trunk.
Basically moss looks for a nice place to hang out. It's not good at competing for space. Any open soil or tree branches are candidates. Moss on tree trunks doesn't hurt anything. It often grows on the shady north side of the tree. Just enjoy the colors of moss or lichens decorating the trees. I call it "tree bling".
Moss invading lawns is a problem typical in shady locations, but this time of year may appear in sunny spots. Moss thriving in lawns signals that grass is weak and has thinned for some reason, allowing the moss to take over. Moss is not really the problem. UI Extension website http://www.urbanext.uiuc.edu/lawntalk/ offers these suggestions for moss in lawns.
First figure out why the grass is not growing and remedy the problem. In addition to excessive shade, other causes of grass thinning and moss invasions, include compacted soils, poorly drained soils, low soil fertility, high or low soil pH, and poor air circulation. Poor lawn care practices are another source of moss problems. General lack of care, including irregular mowing and little or no fertilizer applications are common problems leading to poor turf growth.
Adding limestone is a common "remedy" mentioned for moss control, but is not suggested unless a soil test has shown the pH needs to be raised. Acidic soils are not the only reason for moss in lawns. Adding limestone without a soil test can add to the problem.
Ferrous ammonium sulfate or ferric sulfate (iron sulfate) can be used to control moss to some extent. The moss will temporarily burn away, but tends to return quickly unless site conditions are changed and new grass added. So save your money by not buying moss killing products and instead concentrate on improving the lawn grass. Raking out moss is another option; followed by reseeding with an appropriate grass seed. April is a great time to seed grass in these bare areas.
Modifying site conditions to favor lawn grasses and discourage moss is a suggested way to manage the problem. Too much shade for acceptable grass growth is common. Pruning trees and shrubs to improve air circulation and light penetration may help. Evaluate the site to assure the proper grass for the conditions is being planted. In excessively shady areas (those that receive less than 4 hours of sun a day) ground covers may be a better choice than turfgrass.
Take a good look at the soil conditions. Reduce soil compaction by core aerifying. This may also help correct drainage problems; although serious drainage problems may require more extensive work to correct.
Evaluate lawn care procedures, especially fertilizing, and adapt to the conditions, such as shade. Mow higher (near 3 inches), and fertilize less in shade, as too much nitrogen can be detrimental to shade lawn species. About 1 to 2 pounds of actual nitrogen per 1,000 square feet per growing season is all that is needed. Reduce traffic over lawns in the shade.
Mow on a regular basis (based on rate of lawn growth) to avoid removing more than one-third of the leaf blade at any one mowing. Also avoid excessive watering, as this may contribute to moss problems. Water deeply and as infrequently as possible, based on lawn needs.
From asparagus to wildflowers check out UI Extension website http://web.extension.illinois.edu/state/hort.html for answers to all your gardening questions. Or contact your local county Extension office.