All About Mulch


PLANTS HAVE THE UNFORTUNATE CONDITION of not being able to walk over to a shady spot when the 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:

Benefits of Mulching

  • 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 course, 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.

Pecan mulch
Native hardwood mulch.
Recycled glass mulch
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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 such as 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.

Let it Rot!: The Gardener’s Guide to Composting – Kathleen Bond Borie and Stu Campbell (1988)
The Rodale Book of Composting: Easy Methods for Every Gardener – Deborah L. Martin (1992)

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