Lawn Moss Control

Targeting the Causes of Moss Growth

Lawn moss can be a troublesome weed and is not easy to control. Moss is a very simple type of plant that lacks conventional roots, stems, and leaves. It is very hardy and will grow almost anywhere but commonly grows in clumps or mats in damp and shady locations. In lawns, it does not kill grass but takes advantage of bare and thin areas where grass has trouble growing.

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Pictures of Lawn Moss

Lawn Moss Control - How to Kill Moss
Thin lawn taken over by moss

The key to moss control is understanding the site conditions favoring moss growth and then altering them to encourage healthy grass growth. The best weed prevention is a healthy, dense lawn — moss will not grow where the grass is thick and vigorous.

The site conditions that favor moss growth include:

  1. Insufficient sunlight due to shade
  2. Low fertility
  3. Poor drainage
  4. High soil acidity
  5. Excessively wet soils
  6. Shallow, rocky soils
  7. Soil compaction
  8. Too much thatch

Lawn Moss Control: Altering the Site Conditions to Encourage Healthy Grass Growth

1. Cool, Moist, Shady Locations

Lawn Moss Control - Prune trees and shrubs to increase direct sunlight

In-home lawns, the usual cause of moss growth is insufficient sunlight due to shade in combination with excessively wet soils.

Solution: increase direct sunlight by pruning trees and shrubs to allow sunlight to filter down to the grass. Select shade-tolerant grass types such as hard fescue or rough bluegrass to overseed or plant in these areas.

2. Proper Lawn Fertilization

Thick, healthy lawns require fertile soils while moss has a low nutrient requirement and will thrive in nutrient-depleted soils.

Solution: make sure your lawn is properly fertilized. Take a soil test to see if fertilizer or lime is needed. The soil test will determine the levels of the major nutrients and the report will suggest amounts of fertilizer to apply.

3. Excessively Wet Soils

Usually caused by frequent irrigation, over-watering, or poor drainage.

Solution: water smart, irrigate deep and infrequently. The best way to water your lawn is by soaking it so that the water moves deep into the root system and then letting it dry out between watering. Improve drainage by grading or installing a drainage system.

4. Low Soil pH (acidic soils)

The ideal soil pH for growing most grass types is between 6.0 and 7.0.

Solution: lime applications can be used to raise the soil pH. The only way to know if your pH needs to be adjusted with lime is to have your soil tested. The results will tell you if you need to apply lime and how much.

Lawn Moss Control - Fertilize and Lime

5. Soil Compaction

Compacted soils do not allow air, water and nutrient movement to the grassroots.

Solution: core aeration will reduce soil compaction and will also help break down the thatch layer.

6. Shallow, Rocky Soils

Moss will grow in shallow soils while a healthy, vigorous lawn needs between 3 and 6 inches of topsoil.

Solution: add topsoil and compost to shallow areas.

7. Excessive Thatch

A heavy thatch layer will reduce turfgrass vigor and allow moss to grow.

Solution: manage lawns to keep thatch in check. A major cause of excessive thatch is over-watering and over-fertilizing. Dethatching by power raking will remove excessive thatch and moss.

How to Kill Moss

There are products available that will kill or injure moss, slowing its growth. Killing moss will not prevent regrowth unless the site conditions do not change to favor healthy grass growth.

Lawn Moss Control - Lawn Care

Moss can be killed with products containing ferrous sulfate, ferrous ammonium sulfate, including Moss-Out, MossEx, and a variety of Lawn Fertilizers with Moss Control; or moss & algae killing soaps such as Safer’s. None of these materials pose serious threats to the environment; in fact iron and sulfur are essential nutrients for grasses and tend to improve their color. ~ WSU Extension

The use of these products in combination with aggressive power raking is a good way to remove patches of lawn moss. Follow up moss removal with re-seeding the bare areas to prevent moss and weeds from returning.

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