As lawns green-up and resume growing across Wisconsin this spring, some areas may have more moss than grass. There are several reasons why this occurs, as moss is not an aggressive plant like some other weeds that may invade lawns. Correcting the cause of lawn decline that leads to moss development is the key to solving moss problems.
Two common underlying causes typically attributed to moss issues on lawns are shade and acidic soil. Shade is usually a major factor, as lawns commonly decline in these areas allowing the moss to develop. Acidic soil can be another reason, although not as common as often thought. Unfavorable soil pH, both acidic and alkaline, along with low overall fertility may be involved.
Poor drainage and soil compaction are also common issues causing lawns to struggle, but conditions that are tolerated by moss.
Carefully assessing all these factors and conditions occurring on the specific site where moss has become an issue is necessary before taking steps to solve the problem. A soil test is an ideal starting point, as soil test results provide a soil pH value. Despite what is sometimes written or shown on gardening videos, do not assume moss is always growing on acidic soil. Always refer to soil test results. If acidic, limestone can be used to raise the pH and if alkaline, sulfur will lower the pH. How much to add of either one is based on the actual soil pH determined via soil testing.
Fine fescues are the best choice for lawns in shade. These include chewings, creeping red, sheep, and hard fescues. These are the primary components of commercially available shade lawn seed products. Two significant lawn care adjustments for shade lawns are fertilizing less and mowing taller. Apply half as much nitrogen in shade as compared to full-sun lawns over the course of the season. Excess nitrogen can lead to decline of lawns in shade. While a mowing height of three inches or higher is recommended on most lawns, it is especially important in shady areas.
Surface drainage and soil compaction issues, which contribute to lawn decline and moss development, can be corrected by core aerating. Core aerators that pull up cores and drop them on the soil surface are best. Consider aerating in spring or fall. Core aerating is also beneficial for tree root systems, so this practice can be done under trees.
Finally, another consideration in managing chronic moss and poor condition shade lawns could be converting problem areas into another type of planting. There are numerous shade tolerant ground covers or other shade loving plants to investigate as potential alternatives to lawns.
Bruce Spangenberg is a Horticulture Outreach Specialist with UW-Madison Division of Extension. Get answers to your lawn, landscape, and garden questions anytime at www.go.wisc.edu/GardenQuestions
By Bruce Spangenberg, Horticulture Outreach Specialist, UW-Madison Division of Extension
