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I love it when I get questions to which I don’t know the answer.  It gives me a chance to learn more too:

“Hi, I have read of the benefits of using rock dust in the soil andwanted to know your experience or opinion about using it. Also, do youknow of a source in the LA area?  Thanks, Alan”

Alan, I’ll be honest – I’ve never used rock dust in my garden, but I’ve done a bit of research to answer your question, and I probably will give it a try myself.  Here goes:

What is Rock Dust?

Rock dust is crushed basalt rock, and is usually a by-product of the gravel industry.  It’s what’s left after breaking up stone into smaller bits.  (I always like to know where my soil amendments come from).  Rock dust contains minerals and nutrients – phosphorus (P), potassium (K), iron, magnesium and calcium – all good for your garden.

What does Rock Dust do?

Rock dust basically mimics the way the earth used to be.  Back when the glaciers receded, minerals were left behind in our top soil.  The practice of agriculture pulls those minerals out of the soil and can be difficult to replace (compost replaces nutrients like NPK, but not minerals).  Over the years, gardeners have experimented with adding rock dust mixed with compost (about 50/50 or less rock dust to compost) to their gardens with increased yields.  Some say really increased  yields.

For a little history about rock dust, check out this great article from Garden’s Alive that does a great job of explaining what it is, why it works and where to find it:

http://www.gardensalive.com/article.asp?ai=953

Here’s another informative article about rock dust and its benefits: http://davesgarden.com/guides/articles/view/727/

Now, as with all soil amendments, it’s important to remember that most are waste-derived, which means that they’re not always pure as the driven snow.  Make sure you check out your supplies for heavy metal content and other unsavories:

WSDA Fertilizer Content Search
Where to get Rock Dust?

You can buy rock dust from Planet Natural or Peaceful Valley Farms in 50 pound bags online (split an order with a friend).  Locally in Los Angeles, you might try calling your local nursery or Topanga Seed and Feed or Malibu Feed Bid.  Also, the Garden’s Alive article above mentions that you might be able to go to your local quarry or gravel pit and get some from them.  Gravel people don’t call it rock dust, but any one of these names:  “pond sand, pond silt, pond fines or swamp sand; crusher screenings, crusher fines, bug dust, float, fill sand, or flume sand.”

Thanks for writing in, Alan.  I hope this helps.

Hey fellow gardenerds – have you had experience using rock dust in your garden?  Share it with us here.