Wild About Texas – October, 2007

Plants have the unfortunate condition of not being able to walk over to a shady spot when the Texas sun gets too hot. But you can help them out by providing root protection in the form of some kind of mulch. In addition to keeping the soil and roots cooler, here are some other benefits that mulches can provide:

inhibits germination of weed seeds

reduces evaporation of water from the soil

lessens soil temperature fluctuation (cooler in summer, warmer in winter)

adds organic matter (organic mulches) and minerals (mineral mulches) as it decomposes

diminishes erosion during heavy rains

lessens compaction on areas with heavy foot traffic (organic mulches)

gives a more “finished” look and contributes to the “style” of garden

may help hide irrigation systems

“Organic” mulches are those that are made up of plant parts such as pine bark, leaves, hardwood and cedar mulches. Gardeners often use these to add organic matter to the soil as they decompose.

“Mineral” mulches are those such as decomposed granite, limestone sand, pea gravel, or recycled glass. These materials are typically coarse, allowing moisture to drain away from the base of the plant.

Another method of “mulching” is to use a groundcover as a living mulch. Many native plants are dense and vigorous enough to push most weeds out of the garden and shade the soil from the baking sun. In addition to regulating soil temperature fluctuations, groundcovers also minimize erosion, reduce evaporation and can certainly be beautiful. Gregg’s dalea (Dalea greggii), zexmenia (Wedelia texana), Texas lantana (Lantana urticoides), Lindheimer’s muhly (Muhlenbergia lindheimeri) and snakeherb (Dyschoriste linearis) are all plants that serve as wonderful living mulches. For more information about these plants, visit the Wildflower Center’s Native Plant Information Network at www.wildflower2.org/NPIN/Plants/plant.html

Good mulching practices:

Organic mulches may hold too much moisture during wet spells for plants that prefer dry conditions. Pull mulch back 2 or 3 inches from the stem of the plant or use a mineral mulch.

Match the mulch type to the site conditions and plant requirements. Some native plants thrive in leaner soils. Decomposing organic mulches can provide too much organic matter, resulting in fungal problems. A mineral mulch would be a better choice for native plants that are adapted to soils with relatively little organic matter or dryer conditions. These types of plants include blackfoot daisy (Melampodium leucanthum), gayfeather (Liatris mucronata), Bluebonnets (Lupinus texensis) and many species of cacti.

How much mulch is too much mulch? Layers that are too thick can absorb moisture from light rains, preventing percolation through to the soil. Soaker hoses or drip irrigation under the mulch layer mitigates this effect.

Some mulches form a hard crust or tight mat, shedding water altogether. Again, soaker hoses or drip irrigation under the mulch can solve this problem.

Mulching inhibits all seeds’ growth, so leave seeds you may be trying to germinate uncovered.

About the author: Andrea DeLong-Amaya is Director of Gardens and Growing at Lady Bird Johnson Wildflower Center in Austin. Find out more about native plants on the Wildflower Center Web site at www.wildflower.org

Posted by Neil Sperry
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