How to keep moss from overtaking the lawn
Tim Johnson, Chicago Tribune, January 20, 2012, link
Q: We have 2 1/2 acres with a beautiful lawn and wonderful oak trees. The problem: Moss seems to be taking over. Everywhere I look there is more moss. Is there something I can do to control it?
— B. Wiley, West Chicago
A: Moss invading lawns is not unusual, especially when site conditions are shady. Moss can out-compete lawns when the conditions are better for moss than for grass. Your moss is a signal that your grass is weak and has thinned for some reason.
Moss prefers sites that have poor drainage and are shady and damp with acidic soil. Turf grass does not perform as well in those conditions. The shade in your lawn will have increased as the trees have grown, which may explain why the moss has increased over time. Grass evolved to grow in full sun.
Managing your site conditions will be the best strategy to improve your lawn. Start by reviewing your lawn care practices. Mow your lawn so it always is at least 2 1/2 to 3 inches tall, so the grass can develop a better root system that will help it resist stress and will help choke out competitors. Core-aerating your lawn will help reduce compaction and encourage a stronger root system.
Established lawns in shade require less fertilizer that those in full sun, so apply only 1 to 2 pounds of nitrogen per 1,000 square feet of shady lawn per season. If you are irrigating your lawn, switch to watering less frequently and more deeply. Soils in shade take longer to dry out, so watering the lawn three or more times a week will help the moss and discourage the grass. Most likely, you would be fine with one supplemental watering per week. Water only if there has not been adequate rain.
Have a soil test done to see if you need to apply lime to make the lawn less acidic. (Many soils in northern Illinois are alkaline, so adding lime probably is not necessary.)
You could consider some pruning of your oak trees to increase the amount of light for the lawn, but use pruning practices that favor the health of the oaks over the health of the lawn. Lawns are easier to replace than trees. It is best not to make major changes to the grade of the soil where the oak trees are growing.
You also should consider overseeding the lawn with a good-quality shade mixture of grass seed. Broadcast the seed right after the core-aerating or use a slit seeder, which is a machine that will cut a slit in the ground and drop in the grass seed into it. Using the slit seeder will likely be most effective.
In deep shade areas, consider replacing the grass with a shade-tolerant groundcover, which will be better adapted to handle life beneath trees.