Extension Educator, Horticulture
I happen to like moss. It looks so soft. If I were a leprechaun, it's where I would doze away the summer. Not everyone shares my love of moss since I do 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 the side of a tree trunk.
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 on trees.
Moss invading lawns is a common problem typical in shady locations. Moss comes in when grass is growing poorly. Bruce Spangenberg, former Extension educator, offers these suggestions about moss in the U of I Extension website http://www.urbanext.uiuc.edu/lawntalk/
In addition to excessive shade, other causes of moss invasions, include compacted soils, poorly drained soils, low soil fertility, high or low soil pH, and poor air circulation. Moss thriving in lawns signals that grass is weak and has thinned for some reason, allowing the moss to take over. 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 may add to the lawn 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 fairly quickly. Raking out moss is another option; usually followed by reseeding with an appropriate grass seed.
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 a common underlying cause for moss invasion. Pruning trees and shrubs to improve air circulation and light penetration is a good starting point. Evaluate the site to assure the proper grass for the conditions is being used.
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 three inches), and fertilize less in shade, as too much nitrogen can be detrimental to shade lawn species. About one to two 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. Also avoid excessive watering, as this may contribute to moss problems. Water deeply and as infrequently as possible, based on lawn needs.