Mad About Mulch

Mulch by Russ on Flickr

If you are not going to be gardening for fall, or keep a smaller garden in the cool seasons, it’s time to begin putting beds to rest as their crops play out.  If you planted only in a single wave in spring, determinate tomatoes, summer squash, cucumbers and even many winter squash have finished their life cycles and are dead, dying, or just failing to produce more fruit.  After you’ve cleared away the old plant material and any other debris, put a few inches of mulch on top.

Why Mulch

Mulch has numerous garden benefits:

  • Mulch suppresses weed seed germination
  • Mulch conserves moisture in the soil, which is a benefit even when plants aren’t growing: soil infauna like worms, fungi and bacteria need moisture to thrive
  • Mulch adds to the fertility of the soil as it decomposes
  • Mulch prevents soil erosion

Choosing a Mulch

For garden growing areas, you only want to use a biodegradable mulch, like straw, wood chips, pine needles or shredded tree leaves.  You can use composted manure, but with manure and straw, be wary of persistent herbicides.  You can also extend your mulch with shredded newspaper and paper, but don’t use too much newspaper as it tends to mat down and make paper mache, starving the soil underneath for oxygen and water.  My favorites are:

  • Arborist wood chips are often available for free from tree service companies, who even deliver.  Don’t expect wood chips on demand: these companies will drop off a load when they are in your area.
  • Pine needles are great for pathways in the garden.  Stack pine needles deeper than you think you’d want.  They compact down quickly.  Pine needles are also easy to rake away from garden beds in the spring.

Mulch Myths Versus the Facts

  • Straw, hay and grass clippings have weed seeds.  Very true, and one of the reasons these are not a favored material of mine.
  • Pine needles make the soil acidic.  This common advice — or warning — is just wrong.  Fresh pine needles are indeed slightly acidic (6.0-6.5 pH), as are fresh pine chips.  But when they biodegrade, they are no longer acidic and do not affect the soil pH.
  • Wood chips rob the soil of nitrogen.  Mostly untrue.  As organic materials decompose, they temporarily bind nitrogen and then release it when fully decomposed.  Since wood chips take longer to decompose, the theory is that they will tie up nitrogen in the soil.  In reality, wood chips do not suck nitrogen deep out of the soil like iron filings to a magnet.  What does happen is that there is a sharp reduction in nitrogen at the thin layer of contact.  This is one of the ways that mulching helps reduce weed germination.  Needless to say, it can also reduce germination of vegetable seeds, so remove wood chip mulch from the soil surface when sowing seeds, and don’t use wood chips as mulch around seedlings and shallow rooted vegetable plants such as in containers and “square foot” or “square inch” methods.
  • Wood chips from some trees kill other plants.  Part true. Juglans species, such as Black Walnut and Pecan, produce an herbicide called juglone.  While it doesn’t have much effect on established plants, it can harm seedlings.  Cedars and junipers are often also labelled as killer mulches, but these are perfectly safe to use.
  • Wood chips transmit disease.  Myth.  When this theory is put to the test, it turns out they don’t transmit disease when used on top of the soil.  Back-filling soil with mulch, as in hugelkulture, does create a potential disease vector.

Go mulch!  The benefits far outweigh the cons.  Mulch feeds and protects your soil.