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Is moss taking over your lawn? Spring is an excellent time to eradicate it.

Moss is generally caused by compacted soil, sour soil, overwet soil, too much shade or improper fertilization. Through a process of elimination you can determine which of these conditions is responsible, so it can be corrected. It is important to understand that until the cause is eliminated, moss will continue to grow in the affected area.

The first job is to kill the moss. There are several chemical moss-killers available at local garden outlets. Ferrous ammonium sulfate is the material most-often contained in such products and it will turn moss black in a short period of time. Once it has turned black, rake it out of the grass. Should bare spots remain, prepare the soil and reseed the affected areas.

Lawn moss control products are available under many different brand names. Some of the spring fertilizers also contain a moss killer, so you can accomplish two jobs at the same time if you have not already fertilized. This may be the easiest and most economical way to remove the moss. Follow application directions on the label of the product you use.

Once the moss has been eliminated, it is time to correct the soil condition that caused it to flourish. As I have already mentioned, it will return until the cause is removed.

The best way to find out what is causing the moss to grow is to cut a 4" X 4" plug of grass from the affected area for observation. Examine the grass plants and the soil in which they are growing. Here is what you should look for:

Compacted Soil - Hard pan or clay soil composition; restricted root growth.

If the problem is compacted, sour or poorly-drained soil, it is a good idea to perforate the lawn area with an aerating machine, a manure fork, pitchfork or spading fork. This will allow for better air circulation and will permit water and nutrients to get down into the soil where they can do some good. If possible, perforate to a depth of at least three to six inches. The holes should be about four to six inches apart. If the area is shady or if you have not fertilized properly in the past, you still may find it necessary to perforate the lawn.

Sour Soil - Sour odor.  A soil test will verify this. Contact your local County Extension Service for details.

If you determine that the soil is sour, calcium should be applied to the lawn area as an additional corrective measure. It is a soil sweetener and can be applied after the grass has been fed. Dolomite lime is often recommended for this job. It should be applied at the rate of 40 pounds per 1,000 square feet. This product will also add magnesium carbonate to the soil, an element often lacking in the lawns of this area. One application will probably not be sufficient to correct the soil condition; in fact, a second application in the fall and a third the following spring may be required. Spreader settings generally appear on the bag.

Over-wet Soil - Compacted soil that water cannot penetrate. Sour soil can be detected. Low spots in the lawn can also be the cause.

If the cause of the moss is overwet soil and compacted soil is not the problem, drainage should be improved by filling in the low spots, then reseeding. Perforating will help improve drainage if compacted soil is the problem as discussed above.

Too Much Shade - Wrong type of grass seed used.

When moss is caused by too much shade, one solution may be to eliminate the grass in that area. Ornamental flower and shrub beds can be created and shade-loving plants added. Where removing the grass is impractical or undesirable, shade type grass can be used. Such products are sold under that title or may be referred to as fescue mixtures.

Improper  Fertilization - Limited root growth; sickly green color.

If improper fertilization is the cause of the problem, start a regular feeding program at once. The grass needs to be fed in spring, summer and fall with a well-balanced fertilizer. Avoid brands that have a high nitrogen content; they tend to stimulate top growth only.

If high nitrogen fertilizers are used, they should have a calcium base and should only supplement the use of well-balanced types. If you have a moss problem and use ammonium sulfate as a supplement during the summer months to improve color, substitute calcium nitrate instead. The calcium will be beneficial in sweetening the soil. However, high nitrogen fertilizers do not provide all the nutrients the lawn requires to maintain good health and vigor.

Once you have solved the cause of the moss in your lawn, the grass should be much easier to maintain. Arrange a regular schedule for mowing and be sure the mower is set at the correct height. Most Northwest lawns contain bent and fescue grasses and should be cut at the 3/4 inch height; bluegrass lawns should be cut at 1 1/2 inches.

Be sure to provide sufficient water during the dry season and undertake insect or disease control if either becomes necessary. But, by all means eliminate any moss that may be growing and correct the cause. It will then be much easier to keep the lawn looking nice throughout the entire year.

See Also: Moss in the Garden


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