Saturday, August 2, 2003

Submitted by Calvin Finch, Ph.D., Conservation Director, San Antonio Water System, and Horticulturist

 

ORGANIC MATERIAL AND WATER CONSERVATION

 

It is not romantic or flamboyant but there are several ways of using organic material that contribute to successful gardening and reduce water needs. Consider soil preparation, lawn top dressing, and mulching.

Not very many new homebuyers think about soil preparation when they purchase a new home. I cannot remember ever seeing a new home wish list with compost-enriched soil on the list along with drapes, new furniture, and new refrigerator. It should be, however, because, in the long run, a poorly prepared lawn will cause you ongoing stress and expense.

Every lawn in the San Antonio area should have at least 4 inches of soil under any lawn grass and 2 inches of compost should be incorporated into the soil. With 4 inches of soil your lawn can prosper with irrigation once per week and take advantage of rainfall. The soil is the reservoir for the lawn. It is where the lawn obtains nutrients and water. If there is less than 4 inches of soil and the soil does not contain organic material, there is very little reservoir. It does not matter if we get a good rain; there is no soil to store water until the roots can utilize it.

If your new home site does not include at least 4 inches of soil and you are not interested in adding compost, stick to native plants and a rustic Hill Country look. The native landscape can survive and will not bankrupt you trying to keep it watered. The good news is that the Greater San Antonio Builders Association (GSABA) is taking the leadership on this issue. Beginning in January 2006 they will support an ordinance requiring 4 inches of soil under all new lawns in San Antonio. In the meantime, SAWS will help cover the costs of a low-water-use landscape (including soil) for new homebuyers with the Welcome Home rebate. Check the SAWS website at saws.org or call Karen Guz at 704-7354 for more information.

The next logical question is “how do we add organic material to an established lawn?” The answer is “top dressing.” Top dressing is compost that is added one half inch deep to an established lawn. Some top dressing mixes include sand. To me, sand is cheap filler. Use the potent part of the mix, pure compost, to achieve the most effect for your dollar. Apply the compost after a yearly or bi-yearly aeration and the impact is especially desirable. Compost in the root zone improves both drainage and water-holding capacity by contributing to soil structures that have large and small air channels. The water stores in small channels, but air and excessive water can move through the large channels.

Apply the compost by shovel in December through March or have it applied by machine by Oak Hills Top Soil (830-249-3575). The material costs about $25/cubic yard delivered or about $55 to $65 applied. A cubic yard covers about 650 sq. ft. of lawn, a cheap way to invigorate the turf. Malcolm Beck at Garden-Ville and Kenny Weir at Fertile Garden Supply estimate that compost applied to the lawn can save 50% of your water needs. It may not be that much, but it is certainly enough to quickly repay your investment in water cost saved in just one summer.

Mulch is another important use of organic material to save water in South Texas. An organic mulch of leaves, shredded brush, bark, or lawn clippings reduces water evaporation from the soil surface. As an added dividend, mulch keeps the soil cool so roots can function near the surface, prevents soil compaction, reduces weed germination, and decomposes to provide the same benefits as compost.

Apply 4 inches of shredded brush on the soil surface over the roots of newly planted trees and shrubs to increase the growth rate by 40 or 50 percent over plants where the grass is allowed to grow over the roots. Use live oak leaves 2 inches deep in the vegetable and flower gardens to reduce water needs and increase performance. Combine mulch with drip irrigation and your gardens are almost as water efficient as xeriscape plants. In your containers add 1 or 2 inches of cocoa shell or coarse compost as a mulch for an attractive look and improved performance.

Mulch, the use of compost in soil preparation, and top dressing will save water and make your plants perform better.