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Mulches: So Many Choices
The Coast Gardener Newspaper and Web Column - May 5, 2008

Now is the time of year when gardeners across the state of Mississippi and Southeast are busy preparing and planting our gardens. One of the most beneficial garden chores is applying a layer of mulch in the garden.

Mulches are beneficial in several ways.

It helps us conserve a very precious resource, water. By creating a barrier between the soil in the air, mulch helps to hold moisture in the soil and reduce evapotranspiration.

Mulch also helps us control weeds in the garden. When used in a layer 2 to 3 inches deep the mulch blocks sunlight needed by many weeds seeds to germinate.

Mulch also acts as a thermal barrier moderating soil temperature. In the summer it helps to keep the soil cool while in the winter mulch helps to keep the soil of that warmer than ambient temperatures.

Organic mulches will break down and decompose and add tilth and structure to our native soils.

And last, but certainly not least, mulch can be an aesthetically pleasing addition to any garden.

When you go to your favorite garden center there are so many to choose from. There are mulches such as chips, shredded, nuggets made from pine, cypress, eucalyptus, and just plain old wood. All are available in designer colors. There are cocoa, pecan shells, rock of all different shapes and sizes, and even imitation wood mulch made from shredded recycled tires (steel belts removed). And what about landscape fabrics. Where do those go?

But what kind of mulch do we choose? We can classify mulches into two groups: organic or inorganic. Organic mulches are materials that will decompose and must be reapplied periodically. Inorganic mulches are materials that are inert and will not have to be replied.

Organic mulches

• Pine
  • Bark: pine bark is a classic mulching material that has been used for many, many years. It is available in big chunks all the way down to the very fine, almost dust like consistency.
  • Needles: the use of pine needles as a mulch and material is a true Southern tradition and is a very effective mulching material.
• Cypress: It is desirable because it holds its color and does not tend to float out of the bed during heavy rain. There is concern however that the harvest of our native cypress trees will allow for more storm damage in the future as these trees evolved as a natural storm buffer along the Gulf Coast. Whenever possible, choose another mulching option.
• Eucalyptus: This material has been showing promise as a mulching material. It exhibits some insecticidal properties that may be of benefit in the deterring termites. It is similar to cypress mulch, but these trees are grown and harvested in a sustainable manner.
• Woodchips: These tend to be a readily available and possibly cheaper alternative to some of the other mulching materials. Woodchips however, will decompose very quickly and require frequent replenishment.
• Cocoa shells: Cocoa shells are interesting mulching material. This byproduct of the manufacture of chocolate when used in the garden will release a nice “chocolatey” aroma during warm humid weather. This aroma will decrease over time.

Inorganic mulches

• Stone: All kinds of shapes sizes and colors are available to suit your personal taste
• Landscape cloth: When using stone as mulch you really need to put a layer of landscape cloth to act as a barrier to prevent weed growth. I never recommend using landscape cloth under organic mulches.
  • Woven ground cloth is desirable if you have trees and shrubs in the landscape bed. It allows rainfall and irrigation to penetrate and allows for gas exchange.
  • Black plastic is generally a bad idea because it blocks water and gas exchange. It should only be used in beds where there are no plantings involved.

How much mulch?

The amount of mulch to use depends on a couple of things, the texture and density of the mulching material being used. The general recommendation is to use a layer 2 to 3 inches thick with coarse textured nugget-type of mulches being up to 4 inches thick.

To determine the amount of mulch needed you need to calculate the square footage of the area and the depth of material. When multiplied together will give you the volume of mulch required. The following table gives examples of mulch requirements. Many garden centers sell mulch in convenient 2 and 3 cubic foot (ft.³) bags. There are 27 ft.³ in a cubic yard (yd.³) if you want to purchase in volume.

Written by Dr. Gary R. Bachman, Assistant Extension Professor of Horticulture, Coastal Research & Extension Center.