Mulch — Are There Alternatives to Bark?

By Ann M. Mason, Fairfax Master Gardener Intern

mulch volcano

Extreme example of mulch volcano

Nature shows us the importance of mulch. We observe that trees drop leaves and needles to form an organic layer that serves to retain water and reduce soil erosion. As leaves degrade, they add organic materials and nutrients, like nitrogen, phosphorus, sulfur, calcium and trace elements, to the root zone. Additionally, the organic layer warms the soil, suppresses growth of other vegetation, reduces rot and soil-borne diseases and improves landscape appearance.

Following nature’s lead, gardeners add mulch around our planted environment: trees, shrubs, perennials, annuals, vegetables — just about anything we plant.

So, with all the benefits of mulching, what are the options? How do we choose the mulch for our location? To start, consider that all mulches have differing characteristics, advantages and disadvantages. And some mulches are better for some applications than others.

Mulches are grouped into organic, inorganic and cover crops considered as green manure. Organic mulches are from plant materials, contributing nutrients as they become part of the soil. All organic mulches need replenishment periodically as they degrade.

Bark mulch is made from byproducts of pine, cypress or hardwood logs. Aged wood chips, especially the larger chip sizes, reduce the formation of a dense, compacted layer that prevents water movement. Freshly cut wood chips form organic acids as the wood decays, which can kill or harm plants. Some trees, like black walnut (Juglans nigra), contain a chemical that inhibits growth of many plants. Sawdust is helpful in acidifying soil around acid-loving plants like rhododendrons.

Straw (not hay) is a good winter mulch for the vegetable garden, but it is flammable and may contain seeds. Pine needles (also known as pine straw) decompose slowly, resist compaction and are easy to use. Shredded leaves are free if you have trees and can use a lawn mower to break up whole leaves into smaller pieces. Grass clippings can serve as mulch. But wait three lawn mowings after an herbicide or fertilizer application prior to using clippings. Grass clippings can pack down preventing water movement unless mixed with other materials like shredded leaves.

Newspaper can effectively control weeds if placed three or four layers deep and covered with some other mulch as a weight. Shredded newspaper works well, too.

Mulch 3-3-3