Moss is part of a group of plants that has several thousand species, according to Clemson University. Moss does not have the typical structure of a plant, lacking the leaf, shoot and root systems. Lawn moss reproduces sexually using spores and spreads quickly through a lawn when proper prevention practices are not followed.
Moss grows in wet soils that do not drain well. This includes areas of the lawn that are bare and shady. Moss also likes acidic soil conditions, thriving where other plants do not. Soils that are compacted are also ideal locations for moss to live. Moss does not attack and kill grass, but grows in areas where grass does not thrive.
To prevent the growth of moss in areas with dense shade, Clemson University Extension recommends planting shade-tolerant grass to prevent patchy areas where moss might grow. When mowing grass in shady areas, it is recommended to mow it at the top of the recommended mowing height. Covering shady areas with mulch will also reduce the growth of moss. Growing shade-tolerant groundcover instead of grass also helps reduce moss in the lawn.
Acidic soil with a pH reading of 5.8 to 6.5 encourages grass growth. Soil with an acidity lower than 5.8 reduces a grass's ability to grow. Moss tends to spring up in the areas where the grass refuses to and thrives in the acidic soil. A pH test will determine the soil acidity and how much lime is required to amend the soil quality.
Soil compaction reduces a soil's ability to drain water properly. Aerating the lawn using a core aeration machine or hand tool will relieve compaction. Aeration removes 3- to 4-inch plugs of dirt from the soil, which increases soil drainage. When the dirt plugs break down on the soil, they eat away at thatch that collects on the lawn. Thatch is dead plant material that refuses to break down and covers the soil of the lawn, preventing grass from growing. Aeration reduces both issues and reduces the occurrence of moss.
Breaking up Moss
Moss is often removed by pulling a rake across it. This will temporarily relieve the problem but will not keep moss from returning. Proper lawn cultivation is required. If moss continues to return, ground limestone and concentrated lime will reduce moss population in the lawn.