Organic Matter

Organic Matter is the result of the decay process of organic residues (plant and animal). Undecomposed organic residues such as leaf litter or thatch is not organic matter. Organic Matter ranges from .5% to 10% and is primarily determined by geographic and climatic conditions. Soils with adequate organic matter (3.0% to 6.0%) will have better structure and therefore better resistance to compaction as well as improved water and nutrient holding capacity.

Organic matter acts as a store house for plant nutrients and improves physical structure of the soil. It has a very high capacity for holding cations as well as soil water. Because of its active holding sites it is also an important factor for determining herbicide selection and adjusting application rates.

In order to consider the various problems associated with organic matter, consider the following scenario. Example: Organic Matter is very low - less than 2%.

  1. Soil will compact very easily. Low organic matter is like trying to bake bread without yeast. The soil is very "flat" and will compact very easily.
  2. Moisture (rain water and irrigation water) will tend to run off the top of the soil instead of absorbing into the soil. The result is the moisture does not reach the root zone and the grass comes under heat stress during the hot summer months. In addition, applied herbicides may not function properly, resulting in poor weed control.
  3. As we watch the lawn show signs of drying up during the summer, we water even more. The tendency is to water the lawn as much as two or three times each day, seven days per week under these conditions.
  4. As a result of these efforts to keep the lawn alive with excess watering, we create a tremendous opportunity for fungus growth due to the heat, humidity, and excessive moisture applied to the lawn.
  5. We now have a "no win" situation. If we do not "over-water", the grass dies. IF we do "over-water", we can have a fungus problem and the grass still dies.


Increase the Organic Matter content of your soil. How do we do this, short of tearing up the lawn and plowing down manure or other high organic sources?

First, Organic Matter can be increased by leaving clippings on your lawn and mowing tree leaves back into your lawn in the fall instead of raking and collecting. However, it is important to note that a "mulching mower" must be used for this process. If there is a lot of grass or leaves it may be necessary to mow the lawn two or three times in order to get the material cut into small pieces and scattered over the lawn. Failure to mulch the grass or leaves completely will result in solid masses of grass or leaves left on the top of the lawn, resulting in the grass dying under the mass. It is also important to note that a mulch layer exceeding one-half inch will severely increase the opportunity for fungus growth under hot and humid conditions. As a result, Central MO Turf Management does not recommend this approach.

Second, an organic compost material should be applied to the lawn each spring and fall. Soils low in organic matter and humus, or with poor tilth and structure, cannot be rejuvenated with chemical fertilizers. With the addition of a little moisture, Organic matter applications will quickly start to improve the condition of the entire plant and soil system, regardless of the current general soil condition. Over time lawns will become thicker and healthier; flowers and shrubs will grow and prosper; and a garden will become more productive.

Other benefits include:

  1. Increases moisture retention capability of soil.
  2. Buffers against excess sodium, magnesium and potash.
  3. Improves soil aeration.
  4. Binds plant nutrients such as nitrogen, phosphates, amino acids, certain sugars and trace minerals in soil for long lasting availability.
  5. Digests dead roots and other plant waste.

The bottom line is, you cannot grow anything in a poor or dead soil. If your Organic Matter content is lower than 3% a systematic plan should be developed to start the process of improving the OM to over 3%. This is not a "one shot" program and must be improved gradually over several years, depending on severity.

Of all of the factors influencing a "great lawn"; organic matter and pH level are probably the two most important items to consider. If these two items are not at proper levels, it is virtually impossible to have a great looking lawn that will stand the test of time.