All about Mulch, and how it’s Different from Compost

Leafgro Compost on the left, and Virginia Pine Fine Mulch on the right

by Susan Harris
It’s spring, and the local gardening email groups are abuzz with questions about mulch, especially:  What to use?  But before we get to what,  let’s look at why we mulch in the first place.

What Mulches Do:

  • Suppress weeds
  • Prevent drying out of soil
  • Prevent erosion
  • Reduce compaction of soil
  • Moderate soil temperature
  • Prevent mud splatter on plant and hard surfaces, like your house
  • Add nutrients to soil AND enable the soil to better use soil nutrients from any source
  • Increase the populations of earthworm and beneficial soil microbes
  • Make gardens look well kept and amenable to planting — like gardens

Why Mulch instead of Compost

Confusion about mulch v. compost abounds, but it’s really easy to remember how they’re different and when to use which one.   Mulch is something we put on TOP of the soil; compost is something we dig into the soil or plant directly IN.  Compost, like the wonderful locally made Leafgro product, is a growing medium - which is exactly why it’s not best to use on TOP of the soil as a mulch – because weeds just LOVE the stuff!   Even if you’ve weeded carefully for years and don’t have to worry about more sprouting up from seeds in your soil, remember that all season long weed seeds will land in your garden from the air, thanks to the wind and the birds.

One more reason not to use compost on top, as a mulch, is that it looks like bare soil, which many of us don’t think is as attractive as a layer of organic mulch.   

When

  • Every year, in the Mid-Atlantic region usually in spring.
  • AND immediately after disturbing the soil, especially for planting something.
  • AND to cover bare ground at any time.

How

  • Remove weeds.
  • Loosen top of soil (a tool called the cultivator does this job very quickly), incorporating what’s left of the old mulch into the soil as you do it.
  • Apply 2 inches of mulch.
  • Never mulch on top of plants or have mulch touching their stems and most important of all, don’t pile it up against tree trunks.  (The result is called a mulch volcano and it’s horrible for tree health!)
  • And avoid putting mulch against your house.

What Type of Mulch to Use

Experts agree that organic mulches are best at improving the soil and moderating soil temperature, and many of us prefer using organic products for lots of other reasons.  So, let’s consider the organic options.

  • The top pick of horticulturists and garden writers seems to be shredded hardwood bark, especially “Virginia pine fines”.  It’ll even bind together and resist washing away on hillsides, according to the Washington Post’s Adrian Higgins.
  • A growing minority of experts are recommending wood chips, including top horticulture professor Linda Chalker-Scott, who disputes the often-repeated caution that wood chips rob soil of nitrogen.  She says this happens only where the wood chips meet the soil, not lower where the roots are, but adds that if you’re worried about this happening, just add a bit of compost first, before applying the wood chips.
  • And my personal favorite is leafmold, made from partially decomposed leaves.  Several nearby jurisdictions, including Takoma Park and Arlington County, pick up leaves, chop them up and age them, then offer them to residents for a reasonable price.   If your garden is large and you need a huge quantity of mulch, this is a great option.  I recently had 7 cubic yards of  Takoma Park’s mulch delivered to my driveway.  It’s not as attractive as bark mulch, however, so I buy a few bags of bark chips every year for the more decorative parts of my garden – around the seating area, and on walkways.

One Response to All about Mulch, and how it’s Different from Compost

  1. John Dawson says:

    I enjoyed your article. Thank you for the link to Linda Chalker-Scott’s article about using wood chips as mulch.

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