Using Mulch in the Garden

close up of a green plant in the ground

Most gardeners have heard many times over the years the benefits of adding organic mulch to the garden. The heat of the summer reminds us of the importance of mulch for moisture retention in the soil and tempering fluctuating soil temperatures. This additional organic layer can help suppress weeds as well as help deter pests and reduce disease issues. It adds nutrients to the soil and builds great soil structure capable of holding more nutrients and water for garden plants to use.

When applying mulch, keep the following in mind:

  • Apply a layer two to four inches deep – more is not better
  • Remove weeds (roots and all) before laying mulch, consider apply a pre-emergent herbicide
  • Avoid using plastics and landscape fabrics under organic mulches – its best to have organic mulches in contact with the soil.
  • Plan for decomposition – it’s a good thing! All organic mulches will breakdown with time and the rate depends on the type and conditions.  They will eventually need to be re-applied.
  • Fungus will sometimes form. Most cause no harm and can be left alone or removed if unsightly
  • Avoid “mulch volcanoes” –where trees trunks are surrounded by a mini-mountain of mulch. Mulch should come up to, but never cover the base of any tree or shrub

Trees, shrubs, herbaceous perennials, annuals, and vegetable all benefit from mulch.  The type of mulch to sue will depend on the plant, location, and gardener preference.  Different types of mulches include:

  • Shredded bark, wood
  • Chipped wood
  • Shredded leaves
  • Grass clippings (dried are better than green)
  • Newspaper (shredded or in sheets)
  • Clean, weed-free straw
  • Pine needles
  • Leaf mold (partially decomposed leaves)
  • Cocoa hulls
  • Mushroom compost
  • Seaweed
  • And more!

Inorganic mulches can also be used, but have fewer benefits.  They include rock, black plastic, landscape fabrics (geotextiles), pebbles, gravel, volcanic rock, and recycled rubber.  While these products will prevent some weed growth and give a decorative finish, they contribute nothing to the soil and can cause the root zones of plants to get excessively hot.  Except for specific situations, these types of mulch are not recommended.

Prepared by Aaron Steil, Assistant Director