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The amount of sand, silt and clay in the soil determines its texture. The soil texture tells you what can be planted, how well the soil drains and how prone the soil is to erosion. A soil with equal parts sand, silt or clay is loam. A loamy soil, built up over the years by decaying organic matter, is loose enough to promote good root growth yet tight and porous enough to hold moisture and nutrients. The ideal loamy soil should be 45% inorganic matter, 5% organic matter and 50% porous space shared equally by air and water. This combination gives the soil plenty of oxygen. Water can move easily through it, but not so quickly that the plant doesn’t have time to use the water.

Soil Analysis

You should have a soil analysis performed on all your projects. Knowing what you have to work with will determine your specifications for soil improvement and perhaps even the plant palette. Contact your state or county agricultural extension office for soil analysis information. It is possible that a local university or area nurseryman may have soil testing services. Charges for these services will vary depending on the agency and the comprehensiveness of testing.

Almost all soil can benefit from improvement. Soil amending should be done four or six weeks before planting by using organic matter.

Organic matter improves the soil by the chemical activity that occurs during decomposition. Some organic matter decomposes too rapidly and causes nitrogen deficiency in the soil. Fresh manures and fresh grass clippings are two examples. This type of material should be composted before being used. Organic matter also loosens tight clay, helps sand hold more water, makes the soil easier to dig and adds nutrients.

Inorganic matter is inactive in the soil and takes up space. It is used to loosen soils such as clay which are too heavy or compacted. Sand, vermiculite and perlite are some examples of inorganic amendments. Two inches of inorganic matter mixed with three inches of organic matter can vastly improve the soils.

Mulching

Mulching is man’s attempt to imitate nature. In undisputed wooded areas you may see layers of dead leaves, twigs, fallen branches and trees. Bacteria, fungi and other simple organisms are breaking down this “tree litter” and turning it into soil.

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The depth of the mulch depends on the type you specify. As a rule, the coarser the material, the deeper it should be applied. For instance, a two-inch layer of cotton seed hulls will have the same mulching effect as six inches of oat straw or four inches of coastal bermuda hay.

The Benefits of Mulching

The benefits of mulching include reduced evaporation, retarded weed growth and moderation of soil temperatures. You can use mulch to separate low-water-use areas of the landscape from turf areas. Mulches can also be used to add visual interest.

Mulch insulates the soil and protects it from the drying and baking effects of summer sun and wind. You will find that soil temperatures fluctuate less. This, combined with less moisture evaporating from the soil surface will promote a more even plant growth rate.

With the use of mulch, the ground is buffered from the force of rain and irrigation water. This reduces soil erosion, compaction and crusting. Mulches also help the soil absorb water more readily and keep plants clean and healthy by preventing soil and disease organisms from being splashed onto plants during rain and irrigation.

Time required for weeding will be reduced because weed seeds have greater difficulty germinating under a mulch cover. Your clients will appreciate reduced maintenance costs.

Your choice of many mulches available will depend on what you think is attractive and the availability of the product. The most commonly used mulches are organic. Pine and redwood bark, shredded cypress, grass clipping, hay, leaves, peanut and cottonseed hulls, pine needles, saw dust and wood chips are all good examples.

You may also specify an inorganic mulch such as gravel or crushed rock. These work well to maintain soil moisture and can be attractive if used in moderation. An inorganic mulch used in sunny areas will reflect and/or absorb heat, which can damage plants. Restrict the use of rock mulch to the outer limits of the property, such as along curbs and driveways to keep heat away from the structure.

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Martha Latta is xeriscape program manager for the city of Austin, Texas, which she has been organizing and implementing since July 1984. She serves as president of the National Xeriscape Council, Inc. and is past chairperson of the Austin section of the ASLA. She is also a member of the Texas Turf Irrigation Association’s water conservation committee.