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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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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 grass is thick and vigorous.
The site conditions that favor moss growth include:
1. Cool, Moist, Shady Locations -- 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 over-seed or plant in these areas.
2. Proper Lawn Fertilization -- Thick, healthy lawns require fertile soils while moss has a low nutrient requirements 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 let it dry out between watering. Improve drainage by grading or installing a drainage system.
4. Low Soil pH (acidic soils) -- Ideal soil pH for growing most grass types is between 6.0 and 7.0.
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
5. Soil Compaction -- Compacted soils do not allow air, water and nutrient movement to the grass roots.
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.
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.
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.