• August 25, 2016

Your soil’s important minerals

Print
Font Size:
Default font size
Larger font size

Posted: Saturday, April 5, 2014 4:30 am

Look up the word “vermiculite” in Henry Beard and Roy McKie’s hilarious “A Gardener’s Dictionary” and you’ll see it defined as an “obscure order of nuns devoted to gardening.” In fact (as opposed to in fun), it is a silicate material similar to mica that is sometimes found in the potting mixes gardeners use to start seeds in spring. The word, from Latin, means “breeds worms.”

I think I can explain that. When my sisters and I were little, we would take a handful of our parents’ vermiculite, pour water on it and watch in awe as the dry, compressed flakes expanded to form wormlike columns. This is what vermiculite does in potting soil: Because it is spongy and absorptive, it holds water, so you don’t have to water a container so often. This is especially important with plug trays or soil blocks into which seeds are sown, where the mix can dry out quickly and put tiny seedlings at risk. Organic matter plays a similar role in soil, but vermiculite, mineral by nature, is sterile and inert, thus protecting the seedlings against a fungus that causes sudden collapse — damping-off — and other ills.

Gardeners don’t use vermiculite quite as much as they used to, in part because of an environmental disaster.

Vermiculite mined at a plant in Libby, Mont., once the main source of the material, was found to be contaminated with asbestos fibers. Though the plant was closed and the industry reformed, people have, to some degree, made the switch to perlite.

Perlite is made from a mined volcanic glass of the same name. As a raw material it contains water, trapped by the rapid cooling of lava.

The moisture vaporizes explosively when heat is applied.

The result is a much-expanded mineral popcorn, white in color thanks to light reflecting off tiny bubbles on the surface of its particles.

It has a texture that retains water on that surface (though not in the volume that vermiculite does) but retains air in the spaces between. That lightens your potting mix considerably, as well as providing valuable oxygen for plant roots, along with better drainage than vermiculite. Most potting mixes contain at least 25 percent perlite, which is why they look as if a takeout container had been chopped into bits and stirred in. But it’s a harmless mineral and, like vermiculite, sterile and inert.

Each material has its uses. For seed-starting, I go with a vermiculite mix for my germination but a perlite mix for growing in pots. A mix containing both also can be valuable. It is easy to mix your own, but make sure you buy horticultural-grade vermiculite and perlite. Both are available from places that sell gardening supplies, bricks-and-mortar and online. If you are using either in quantity — to lighten soil in large containers or even in small garden beds — you’ll want to shop for prices.

Some gardeners use them to store dahlias or bulbs over the winter. Or, as vermiculture mavens consistently do, employ vermiculite as a medium for, yes, breeding worms.

Barbara Damrosch’s latest book is “The Four Season Farm Gardener’s Cookbook”; her website is www.fourseason.farm.com.

More about

More about

More about

Rules of Conduct

  • 1 Keep it Clean. Please avoid obscene, vulgar, lewd, racist or sexually-oriented language.
  • 2 Don't Threaten or Abuse. Threats of harming another person will not be tolerated. AND PLEASE TURN OFF CAPS LOCK.
  • 3 Be Truthful. Don't knowingly lie about anyone or anything.
  • 4 Be Nice. No racism, sexism or any sort of -ism that is degrading to another person.
  • 5 Be Proactive. Use the 'Report' link on each comment to let us know of abusive posts.
  • 6 Share with Us. We'd love to hear eyewitness accounts, the history behind an article.

Welcome to the discussion.

Entertainment Events

  • MLK Grande Parade-2017

    • Mon, Jan 16, 10:00 am CST
    • Midtown Houston, Houston

    The MLK Grande parade Is One Of the Largest Single Day Multicultural Events In The U.S. That commemorate The MLK National Holiday Observance. …

  • MLK Battle Of The Bands Competition Houston-2017

    • Sun, Jan 15, 4:00 pm CST
    • W.W. Thorne Stadium, Houston

    The MLK Battle Of The Bands Competition-Houston Is One Of The Larger High School Marching Band Competitions In the U.S. Featuring 16 Nationall…

  • 23rd Annual MLK Grande Parade

    • Mon, Jan 16, 10:00 am CST
    • Midtown Houston, Houston

    The MLK Grande Parade Is One Of The Largest Single Day Multicultural Events In The U.S. That Commemorate The MLK National Holiday Observance. …