(Editor's Note: This article was originally published on March 2, 2009. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
Moss in the Lawn: How Did It Get There?
Like most other invasives, moss flourishes in areas that are under stress. In neglected lawns, once the rains begin, moss can quickly out-compete the turf-grass. Additionally, moss can continue to grow through the winter, when grasses are dormant. Moss can dominate such a lawn in a matter of months. When conditions become dry, moss growth diminishes, but the plant can tolerate long periods of drought. Once irrigation begins or the rainy season returns, moss rehydrates and continues to grow.
Part of moss's hardiness stems from the fact that it can reproduce either through spores (sexually) or by breaking into smaller pieces, which then grow new plants (asexual). Given the right conditions, moss can spread at an alarming rate, eventually crowding out lawn grasses completely.
What Conditions Favor Moss Growth?
- Thin turf: caused by lack of fertilizer, insect injury (mainly chinch bugs), or heavy de-thatching just before rainy season
- Acidic soil: pH too low for good turf growth; soil has a sour odor
- Heavy shade: insufficient light for good turf growth
- Wet soil: over irrigation, heavy rain, poorly drained soil
- Injury: insects, disease, chemical overuse, or cultural practice such as scalping grass
What Solutions Will Control or Eradicate Moss Growth?
Before trying any control methods, you must determine which of the above-mentioned conditions are causing your problem.
- Soil pH is simple to ascertain. Soil testing kits are available in most garden centers, or soil samples can be taken to your local Extension office for testing.
- Changing the light conditions can be more of a challenge. One approach would be to thin out the shade trees to allow more light to penetrate. A more logical approach would be to redesign the shady areas and replace the turf-grass with landscaping or planting beds. If you must have grass in shady areas, consider replanting with shade-tolerant varieties for your particular region. Fine fescues are good choices for dry shade; for wet shade, try roughstalk bluegrass.
- Excessively wet soils encourage more than just moss growth--they are the perfect environment for diseases and molds. First, be sure to avoid nightly watering. The simplest methods for improving drainage are core cultivation, slicing, or thatch removal. In severe cases of heavy, wet soil areas, the grade might need to be changed, or subsurface drain pipes installed to lower the water table.
- Injuries can more or less be controlled.
- Chinch bugs are the most commonly found pests of turf-grass. As the bugs feed, the process blocks the grass's ability to draw water and nutrients, and the plant dies, leaving yellow patches. Grass that is under chinch bug attack is highly susceptible to moss invasion. Chemical control is the only method found in available research. Check with your garden center or lawn care specialist to find out if consumer products are available for residential use.
- Under-irrigated lawns become debilitated and thin.
- Setting mower blades too low causes scalping in uneven areas of the lawn, leaving them vulnerable to weakness, drying out, and death.
- De-thatching in mid-March through April will remove moss while it is still healthy and growing. In areas of heavy infestation, chemical sprays should be applied after de-thatching.
What Are the Chemical or Alternative Controls?
- The most common chemical most homeowners use as a nonselective herbicide is glyphosate (e.g., Roundup®), however this chemical does not work on most mosses. Professional lawn and landscapers use carfentrazone for moss control, but this is not available for consumer use.
- Many compounds have the ability to suppress moss growth by acting as desiccants. Ground limestone and hydrated lime are two such products, both easy to find and inexpensive. Specific moss control products include iron sulfate (ferrous sulfate), ferrous ammonium sulfate, and copper sulfate; the label will specify moss control. Be aware that the iron and copper materials can damage new grass growth, and should be used with care.
- Alternative methods may be less aggressive in moss control, but nevertheless, do work. Cryptocidal soaps act as contact killers. They are safe on sidewalks, driveways, decks, and other structures.
The key to controlling moss your lawn is vigilance and good turfgrass management. And a lot of patience.
Photo: IvoShandor, used by permission of GNU Free Documentation License, Wikimedia