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How to Control Lawn Moss & Algae

Cultural control and other tips to prevent buildup capable of damaging lawn grass.

Mosses and algae can often appear in areas of a lawn where growing conditions hamper grass growth. Things like excessive shade, acid soil, poor drainage, compaction, poor air circulation and low fertility levels may all contribute. Acid soil (low pH) is most often blamed for moss or algae invasion of the turf, but any factor that leads to poor grass growth can encourage the development of moss or algae in the lawn. Shady low areas which are heavily compacted and often wet for prolonged periods of time are conducive for algae growth.

Algae and moss occur in lawns where conditions are not suitable for growing dense, healthy turf. Mosses are small leafy plants, which appear to be a mass of fine stems (Fig. 1) There are a great number of mosses which are adaptable to a variety of environmental conditions ranging from dry areas to bog-like habitats.

Algae are a group of small, primitive green plants that are often mistaken for moss in moist areas under trees. Algae are not parasitic on grass, but they can produce a greenish to brownish scum on the soil surface (Fig. 2). After the algae have dried, a dark green or black green crust will form on the soil surface. This crust reduces water penetration and air movement into the soil. It must be removed before turf grass can be established.

Cultural Control

  1. Maintain good soil fertility. Always have a soil test done to determine if corrective lime and/or fertilizer applications are necessary to correct soil fertility levels and adjust to the proper pH.
  2. Improve drainage. Soils which are constantly wet because of poor drainage should be graded so that water will move off the lawn.
  3. Provide more light. Sometimes it may be necessary to choose between having trees or a good lawn. Lawn in completely shaded areas will not thrive and the removal of some trees may be the only answer. Oftentimes removing low branches and thinning out branches in the trees allows for enough light so decent good turf can be produced.
  4. Relieve compacted soils. Compacted soil may be loosened by aeration and topdressing the lawn with organic matter. The use of an aeration machine that removes soil plugs will help relieve compaction in the lawn.
  5. Improve air circulation. Removing low-hanging tree branches will help increase air circulation and allow sunlight into the area.

To achieve long term control of moss and algae, it’s important to correct the conditions unfavorable for grass growth. For questions or more information, sign up for our e-newsletter, The Monthly Dirtfollow our social channels or give us a call for the latest seasonal tips and DIY know-how.

Figure 1
Soil surface
Figure 2


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