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Perlite; a great way to improve drainage (And a primer on what 'organic' means)


Q. Dear Mr. McGrath: My wife is an avid listener of your program, planning her Saturdays so that she can be home when your show is on. She suggested I contact you with my small concern that the perlite you often recommend isn't "organic" in any sense that I recognize as a chemist—or probably in any sense that non-scientists use the word, as it is a form of glass (http://www.perlite.net/). Now, this doesn't take away from it being a useful component for gardening as you have advised; the advice is still fine. I would just suggest adjusting your justification of "it's organic." Oh, and rest assured that I am also a listener who enjoys your show. Keep up the good work!

---Harry in Havertown, PA

A. I have to thank Harry for bringing up an important point. In the world of technical chemistry, the word 'organic' has a very different meaning than it does in the world of contemporary food and agriculture. But that's not unusual, as many English words have multiple meanings, like 'bulb', which can refer to an underground plant part, something that gives off light or even a squeezable thing, like the back end of a turkey baster. Context always reveals which version is in play (at least you hope it does, and people aren't burying CFLs in their garden or screwing tulip bulbs into table lamps.)

Let's take a look at the roots of the word 'organic' as we use it in modern gardening and grocery shopping. Back in 1940, J. I. Rodale, the founder of Rodale Press (now known as Rodale, Inc. or just 'Rodale') and originator of ORGANIC GARDENING magazine (titled "Organic Farming and Gardening" during its early years), chose 'organic' from a slew of words that the British were using to try and describe a form of agriculture that shunned the toxic chemical pesticides and fertilizers of the day; things like 'arsenate of lead' and ammonium nitrate—and later, famously, DDT. In its earliest and simplest uses 'organic' meant anything that occurred naturally—like seaweed, manure, rock dusts…

…and perlite, the misunderstood mineral. Harry is correct that perlite is a form of glass; specifically a volcanic glass that is mined and then heated in big ovens until it 'pops' into a round, white material that's used in seed-starting and potting mixtures to lighten the soil, allow more air around the roots of plants and to both help retain water and improve drainage.

A lot of people think that those little white balls are some kind of Styrofoam-type artificial substance—heck, that's what I thought they were my first couple of years gardening! But they are a mined mineral popped into little balls. Little balls that our bulb-happy friend Art Wolk (author of "Bulb Forcing for beginners and the seriously smitten") has raved about on our show, during his lectures at places like the Philadelphia Flower Show, and in his publications.

One of Art's missions as an educator is to beat the importance of air in the soil into gardener's heads, whether they're forcing bulbs in the ground or growing plants in garden beds—and perlite is a great way to do that. You may also recall that the great Four-Season farmer Eliot Coleman listed 'air in the soil' as one of his "three essential keys" in the seaweed piece we did a few shows back.

And I am proud to add that I personally use a lot of perlite. I buy a couple of big bags of it every season and mix lots into my seed-starting mixes>; however much perlite they already contain, I add more. And when I began to worry that the soil in some of my raised beds seemed to be getting a little heavy a few years back, I started mixing perlite into what's otherwise now mostly 20 years of compost. And I add a lot of perlite to my garlic planting beds in the fall to make sure the bulbs don't get waterlogged over winter.

And remember a few weeks back when we reported that Eliot Coleman said that seaweed was the only input he would buy if he didn't live right near a cold ocean where he could get it for free? Perlite is my choice in that category. And since I don't happen to live near an old volcano that's conveniently located next to a giant oven, I do have to buy mine. And I buy and use more of it every year. "Air in the soil"; it's a gardener's second best friend. (After compost, of course!)

And you can be certain that it's organic, because it's a mined mineral; like rock dust and seaweed, it's naturally occurring. It does need to be 'popped' but that only makes it more useful, not unnatural.

And you don't have to believe just me

…because it's also officially organic.

In the early 1990s, the state of California did the hard work of making the first official decisions on what inputs and products would be allowed in what would come to be called 'certified organic agriculture'. Shortly afterwards, the NOSB—the National Organic Standards Board—was formed to codify the Federal regulations that exist today. And part of that 'standard' is that all of the 'materials' or 'inputs' allowed in organic production must be on what's called the "OMRI list"—the official listing of allowed products as issued by the Organic Materials Review Institute. Access their website, type in the name of the product or material you're considering and it'll give you a thumbs up or down.

And with perlite, the thumb is up: "Status: Allowed in certified organic agriculture; a mined mineral."

Case closed. Now, where's my big bag of perlite….?

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