TIFTON — Mulches are very popular in our contemporary landscapes and urban communities, but they are not a new concept by any stretch of the imagination. For centuries, nature has provided mulches in the forests as the leaves and needles dropped to the ground, matted together, and formed a natural protective layer on top of the soil. Many different natural and synthetic mulches are available today which provide curb appeal, reduction of soil water losses, suppression of weeds, and protection against temperature extremes.

Also, mulches in landscape plantings provide other benefits including the reduction of soil erosion and crusting, and the improvement of water infiltration into the soil profile. For example, when water droplets (rainfall or irrigation) make contact with the bare soil, this impact causes the soil particles to scatter in all directions which results in soil erosion, crusting, compaction and slow water infiltration. Many mulches buffer this impact from such droplets providing more favorable growing conditions and positive visual results.

And, mulches improve the soil structure which is critical in plant growth and development. As organic mulches decompose, they provide organic matter that encourages the soil particles to aggregate or come together into larger aggregates. These larger aggregates increase soil aeration and improve moisture conditions and availability. Such conditions favor additional root development and improved biological activity which, in turn, improve soil structure.

A good mulch will be economical (cost effective), readily available, easy to apply and remove, maintain its placement with minimal surface movement, supply organic matter to the soil, and is free of weeds, insects, and diseases. In addition, it will suppress weeds, conserve soil water, and moderate soil temperatures. A super-mulch does not exist and all mulches tend to have their positive and negative attributes in the landscape.

For example, black plastic can be used above the soil and underneath a primary mulch to restrict weeds. However, it heats the soil in summer which can be lethal to plants, restricts water movement into the profile, and holds water at the soil surface which encourages a shallow root system and thus reducing the longevity of the plant. Thus, these negatives far out-weigh any positives that might be achieved.

Straw, shredded leaves, pine needles, and wood chips are effective in curb appeal and as insulating blankets in winter, but they slow the process of soil warming in the spring. Also, pecan shells and cottonseed hulls can be used for mulches. However, pecan hulls attract insects pursuing any minute pieces of pecan that might be left in the hull and birds will scatter the hulls as they search for these insects.

There is not one definitive answer in the selection of a particular mulch to use. But understanding the characteristics and attributes of the different materials which are available can help in the selection of the best mulch to use for a particular location.

 As a general understanding, black plastic, newspaper and straw are commonly used in vegetable gardens or small fruit plantings. Wood chips, bark chunks, and pine needles are appropriate mulches for shrub beds or around trees. Fine mulches, such as bark granules and wood shavings are attractive when used in annual or perennial beds. Fine gravel or crushed stone mulches look most natural when used in rock gardens, xeriscapes or around the foundation.

Commercial bark mulches are categorized based upon particle size including bark chunks (decorative bark), bark granules (soil conditioner), and shredded bark. Of these, bark chunks are the most persistent and desirable. However, some bark mulches may be toxic to young plants, especially if the bark is fresh or if it has been improperly stockpiled or mismanaged. Such toxins can be leached from the fresh bark with multiple applications of water, evaporated by thorough aeration through turning and rearranging the stockpile, and allowed to season for at least three months before using them.

Bark mulches are most likely to cause damage to plants if the mulch particles are small, if the mulch is deep in thickness, or if high proportions of the plant roots are concentrated in the surface layer of the soil. If you are concerned about the toxicity of fresh chips, stockpile them for the specified time before use.

Commercially-available bagged bark mulch products has been allowed to weather for long periods of time to remove any toxins and are least likely to harm plants. The most desirable characteristics of bark mulches include excellent resistance to compaction, minimal movement by wind action, attractiveness or curb appeal, and availability.

Wood chips are another mulching choice made available from many different hardwood and softwood species. Fresh chips have a higher carbon to nitrogen ratio which means that during decomposition they may temporarily reduce the supply of soil nitrogen available for plant uptake. Again, age any fresh chips for about three months before using them in the landscape.

Wood chips tend to lose more of their decorative appearance quicker than bark mulches.  Thus, the frequency of replacement can be higher or more often.

Sawdust can be used as a mulch for blueberries, azaleas, and other acid-loving plants. Sawdust mulch has an acidifying effect on the soil as it decomposes and can also deprive the soil of nitrogen. Keep a regular check on soil pH to determine continued usefulness and feasibility of such mulches, and the chemistry of the soil.

Pine needles have a most pleasing appearance and acidifying effect on the soil around acid-loving plants. They are available commercially and can be raked up from around pine plantings in the woods or off the lawn. Pine needles decompose slowly (but do discolor quickly in the south Georgia heat), are resistant to compaction, and are easy to work. They provide excellent protection and ornamentation around shrubs and trees.  However, if used in deciduous beds, the combination of fall leaf drop and existing pine straw mulch can be an undesirable mix thus creating more work to address in the fall clean-up process.

Matching the mulch to the landscape bed is most critical and should be done after considering all the options. The mineral or synthetic (inorganic) mulches will be discussed in the next article and      do not contribute any beneficial organic matter to the soil as does the organic mulches but they can offer superb curb appeal and low maintenance. Always think of environmental compatibility and sustainability when selecting landscape mulches.