What is mulch? How much should you use?

Mulch is any material, organic or not, placed over the surface of soil. Gardeners like mulch for four important reasons.


  • moderates soil temperatures
  • conserves moisture
  • prevents weeds
  • dresses up the garden

There are many kinds of mulch. Popular ones include:

Stone. Heavy and expensive, but long lasting. Doesn't wash or blow away. Doesn't decompose so therefore doesn't improve soil. Apply 1 to 2 inches deep.
Grass clippings (from weed- and pesticide-free lawns). Free, but often contains weed seeds. Apply 1 to 2 inches deep.
Pine needles. Free if you're near a pine tree. Attractive. Apply 2 to 4 inches deep.
Seed-free straw. Almost always includes some weed seeds. Attractive and inexpensive. Lasts one season. Apply 4 inches deep.
Shredded bark. Attractive. Irregular pieces knit together to resist washing in rain and wind. Lasts at least 2 seasons. Apply 2 to 4 inches deep.
Chunk bark. Various sizes available. Apply 2 to 4 inches deep.

Mulch tips:
  • Avoid mulches greater than 4 inches deep. They might reduce air circulation into and through the soil.
  • Limit mulch thickness around soft-stemmed annuals and perennials to 2 or 3 inches.
  • Don't pile mulch around the main stem of a plant. Doing so might encourage the stem to rot.
  • Spread the mulch to cover the soil slightly beyond the plants canopy.
  • Don't use lightweight materials such as chunk bark in areas prone to flooding. They'll float and wash away.