Have you noticed any masses of light-green, plant-like material growing in your lawn? These are probably patches of moss or algae. Most people notice moss during the summer, but December to March is the best time to control moss problems.
The key to controlling any plant is to know its life cycle and the conditions that favor its growth. Mosses are small, non-parasitic plants spread by spores. They have many thread-like stems with tiny leaves, and they form thick mats on the soil surface. Mosses do not kill turfgrasses. Mosses fill in the space where conditions are poor for grass development and growth. They thrive in shady, wet areas.
Algae are simple, plant-like organisms that form a thick mat or ‘scum’ layer over the soil surface. They are usually green, but also appear in brown or red varieties. Algae need high amounts of moisture to survive. Like mosses, they don’t actively attack turfgrasses, but rather grow in the areas where turf won’t. Mosses and algae like to grow in places that are not conducive to healthy turf. They favor sites that have compacted soil, poor drainage, highly acidic soil, low soil fertility and dense shade. Controlling mosses and algae long-term means correcting these conditions throughout the lawn.
If the area has minimal grass, it is best to renovate the area. Physically removing moss with a rake is one way to get rid of it, but it’s impossible to get every single piece, and there are plenty of spores already in the soil. Remove all vegetative material that you possibly can, scratch the soil and reseed with a turfgrass that best fits the site conditions. Use a tiller to break up the soil down to 6 inches. Lightly-compacted soils can be treated by using a core aerator to take small plugs out of the soil and increase drainage.
Fertilizer and lime can be added as indicated by the results of a soil test. The new turf will grow much better with proper soil pH and fertilization.
Mosses and algae both thrive in highly acidic and low fertile soil. Satisfying the pH and nutrient needs in the soil will aid in removing mosses and algae from the lawn as well as establishing a healthy turf.
If poor drainage is a problem, contouring any low spots in the affected area will improve water retention. In extremely wet areas, you might need to install French drains to rapidly drain excess water. Organic matter can also be added to the soil to improve drainage. If you have an irrigation system, decrease the run time for the zones that cover the areas that are problematic for moss or algae growth.
Because mosses thrive in dense shade, pruning tree branches might be necessary to improve sunlight and airflow. However, this is a limited technique. In most instances, only small amounts of pruning can be done without affecting the overall look or health of the tree. If heavy pruning is not feasible, enlarging the bed under the tree is a great option. Consider using a shade-tolerant ground cover and mulch newly created bed areas under trees; this will discourage moss and algae growth.
It’s common for homeowners to attempt moss control with glyphosate, which is one of the more widely used nonselective herbicides for lawn and landscape use. However, glyphosate does not work on most mosses. There are several chemicals labeled specifically for moss and algae control.
For example, iron sulfates and potassium salts of fatty acids can be found under various brand names at most garden centers and feed stores. Always read and follow instructions found on the label.
Please note that chemicals will only help temporarily. The most effective control is altering the landscape environment to discourage moss and algae growth and promote a healthy lawn.