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This Week at Milberger's

Mulch
By Calvin Finch, Ph.D.

Mulch is an essential part of gardening in South Texas. There is a long list of benefits to the practice of mulching. Saving water leads the list.

When we think of mulch we usually think of organic material like bark or shredded brush but mulch can be any material that covers the soil to reduce evaporation and reduce weeds. Plastic is used quite often in agricultural fields and examples of rock mulches exist in every urban neighborhood. Something that we often overlook as a mulch-like option in our landscape is pervious hardscape.

Flagstone, brick without mortar, and treated wood sidewalks and patios are almost as beneficial as organic mulches over the roots of established live oak trees. You can protect the trees from compaction and still have a usable surface for human activities. Use flagstone, patio blocks and brick without mortar placed into 2-4 inches of sand with a treated wood border, and you have a mulch that protects the roots from compaction, lets water penetrate and allows gases to escape.

As good as inorganic mulches can be for some situations, we usually think the best mulches are organic. They mimic the natural process in the prairies and forests where layers of organic material enrich and insulate the soil as time passes. In the North where cold weather slows the rotting process, the organic material accumulates. Here in the South we are like one big compost pile, and the organic material does not accumulate in the long term.

Mulch saves water by insulating the soil. Mulch also keeps the soil cool. The summer sun beating down on bare soil heats it to temperatures so high that root growth does not exist in the upper 2 inches of the soil. When we only have 4-6 inches of soil we cannot afford to lose the top 2 inches. Organic mulches usually will not eliminate all weeds, but they certainly reduce weed pressure and make them easier to remove.

The best mulch is the one that is the most available. We cannot afford to waste any mulches.

Leaves are great because they are available in the fall when the deciduous trees drop their leaves and then again in March when the live oak leaves fall. I don't know who ever started the rumor that pecan and oak leaves were not good for mulch because of acidity, but they were wrong; use them in your vegetable garden or shrub border. It is a real sacrilege to send leaves to the landfill with the garbage pickup. We waste the organic material, pay to have them hauled away and then waste valuable landfill space.

City of San Antonio residents can get free shredded brush mulch at the 1800 Bitters brush collection site, 7days a week. You have to load it yourself, but the material is excellent for placement over newly planted tree roots and in the shrub border. Three to four inches of mulch over the roots of a newly planted tree increased growth rate by about 40 percent when compared with trees where sod grew up to the trunk.

Bark mulches and cypress mulch are particularly decorative. I like cocoa shell mulch for containers and small beds. It is fine enough that it does not overwhelm small plants. Pecan shells are seasonally available in large quantities. They work fine as long as you do not want to walk barefoot in your mulched beds! Shredded cedar that has leached for a season can be used as thick as you want for mulch.

Compost is a great mulch but is most valuable as a soil enricher. If you use compost as a mulch, cover it with a coarser material like bark or shredded brush to keep weed seeds from germinating and the material from washing away.

Your favorite nursery has bags of mulch. In large quantities, or for more variety, visit Gardenville, Fertile Garden Supply, Living Earth Technology, Keller Material and other suppliers.