Organic matter is vital to a healthy soil. For typical soils, the ideal composition is 25% air spaces, 25% water pores, 45% minerals and 5% organic matter or humus. Unfortunately, it can be difficult to maintain these balances due to soil compaction and to the fact that the organic matter continues to decompose in the soil. Thus, it needs to be periodically replenished and this can be a challenge in ornamental beds and borders.

Fortunately, both heavy clay and excessively sandy soils may be improved by adding large amounts of organic matter (OM). In clay soils, the OM will help to form larger aggregates or clumps which then provide pore spaces generally missing in fine textured clay. This can improve both the air content of the soil and improve the poor drainage typical of this type of soil.

In sand, OM will actually fill some of the very large pores that usually lead to excessive drainage and droughty conditions. Also, the OM will act as a "sponge" to absorb water and prevent it from running swiftly through the sandy soil. The final benefit is that OM has a great attraction to nutrients in the soil and will hold them in the root zone of plants. Sandy soils have little attraction to nutrient elements and they quickly move through the soil with water and out of the root zone of plants.

In addition to these beneficial traits, OM also acts as a great environment for soil organisms. Earthworms and a variety of decomposing organisms thrive in a soil rich in OM.
 

Sources of OM
  • Compost - The most common source of added OM for the home landscape garden is and should be, compost. This can be purchased commercially, from community composting facilities or, best of all, created in the backyard compost bin.
     

  • Peat Moss - For small areas, peat moss is another good source of organic matter. However, due to the cost and concerns over the limited availability of the product, it should be used sparingly.
     

  • Leaves - Although it would be better to run them through a composting process, the use of leaves from the trees in your yard may also help add organic matter to the beds and borders. Incorporate them into the soil as best as possible and they will decompose over the coming years.
     

  • Mulch - A layer of organic mulch such as wood chips, shredded bark or others spread on top of the beds and borders will eventually decompose and mix into the soil. This is a very slow and ineffective way of amending the soils but it does help over time.
     

  • Manures - Animals droppings are, of course, OM, however, there are some concerns that prevent most of us from using them on urban/suburban landscapes. Manures that have been run through a composting process and are broken down into their component parts are no problem. However, fresh manure from the farm or horse stables may have odor problems. Plus, such products have high levels of saturated salts which may "burn" the plants upon contact.

 

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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