May 042010
Protect bare soil with mulch.

Mulch protects the ground by insulating it -- with pine needles, straw, leaves, nutshells and other suitable mulch ingredients.

Mulching is a terrific way to dispose of many organic wastes, and is required for healthy soil if the soil is bare.  Bare soil may be found around shrubs and trees in ornamental beds, or along the side of your house, or a bald spot where you haven’t been able to get anything to grow.  All bare soil should be mulched.


Mulch protects the ground by insulating it.  I performed experiments to measure the difference between mulched ground and bare, exposed soil.  Exposed soil temperatures registered as much as 35 degrees higher than mulched soil in summer heat.  In winter, mulched soil temperatures do not become as cold as those of bare soil.

A big advantage of mulch in addition to the moderation of temperature is the moderation of temperature change.  As the sun heats during the day and cools at night the mulched soil remains cooler during the day and warmer during the night.  The range of temperature is much smaller in mulched soil.  Reduced temperature range in mulched soil makes the environment more stable, thus friendlier for bacteria, fungi, earthworms and other members of the soil food web.

Mulch helps maintain soil moisture by inhibiting evaporation.  A mulch of nut shells, hay or wood chips is easily penetrated by water and will help retain that moisture in the soil.  When you choose materials to use for mulch, be sure that you select something that will not mat.  Paper shreds and un-shredded leaves of some species are not good choices for mulch because they can mat together and prevent moisture absorption and air movement.

Mulch also reduces erosion.  Exposed earth can be susceptible to hard rains or watering.  Mulch should be heavy enough to withstand these forces and remain in place rather than washing or floating away.

Materials Suitable for Mulch

The list of materials that are suitable for mulch is long and varied.  Characteristics to check for are: heavy enough that it won’t be washed or blown away, not easily matted, no chemicals, appearance.

Suitable materials include:

  • Straw
  • Shredded leaves
  • Nut shells
  • Rocks or stone chips
  • Chipped or shredded wood
  • Pine needles
  • Pine cones
  • Crushed acorns

Sometimes, depending on the situation, I use materials for mulch that have inherent problems so I can’t recommend them for all circumstances.  I once acquired a large amount of sweet gum balls.  They made beautiful mulch.  Of course, they contained the seed of the sweet gum tree, so I had to pull out a few sprouts.  I didn’t consider that an inconvenience, but others might.

Laying Mulch

Thoroughly water the area to be mulched.  If weeds are problematic, spread cardboard or a few pieces of newspaper on the ground to prevent weeds from sprouting.  The cardboard or paper will decompose so will not be effective forever, but it will help in the short term.  In the future, weeds that grow up through the mulch should be weaker and easier to remove.

If you choose, you may first spread 1” of finished compost or partially-decomposed compost.

Spread 2” – 4” of mulch.

Avoid spreading mulch right up to the base of any plant.  Mulch should be stopped 3” before reaching the base, stem, or trunk of any plant.  Plants can be damaged fatally if mulch is spread so that it is touching the bark of the plant’s stem.  If you are concerned something will displace the mulch into the space surrounding the base of a plant, you can cut the bottom out of a nursery pot and use it as edging around the tree or plant.  The edging should not be touching the base of the plant.


Soil should be watered with mulch in place.  Water will fall down around the mulch and be absorbed by the soil.  In fact, mulched soil is better able to absorb water than crusted, exposed soil.

Mulch decomposes over time, so check it twice a year and replenish before temperature extremes are expected.

Living Mulch

Another appealing option is to plant groundcover and let that act as living mulch.  I have a spot in my garden where seasonal flowers bloom for only a month or two.  That ground is bare the rest of the year.  So I planted some elfin thyme.  Flowers sprout up through the elfin thyme during their season, and the thyme looks pretty and green there the rest of the year.

Mary Tynes, Master Composter,

  3 Responses to “Mulching”

  1. great post as usual!

  2. That’s very interesting Mary. I knew somewhat that rocks, reg print newspaper and/or cardboard (shredded), leaves and twigs could be used, I never knew that nut shells could be used as well. I also didn’t think about using living mulch either.

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