The next best thing to actually getting my hands dirty gardening must surely be reading about gardening, I've decided. So, since the great outdoors is frozen solid, I've cozied up with The Truth About Organic Gardening: Benefits, Drawbacks, and the Bottom Line by Jeff Gillman. A University of Minnesota professor, Gillman holds a doctorate in horticulture and a master's in entomology, so he knows a thing or two about organic and synthetic fertilizers and pesticides, and he doesn't pull any punches.

Turns out I've been guilty of perpetuating a few of organic gardening's more common myths. For instance, while I once might've encouraged the use of praying mantises in the garden to keep the numbers of insect pests down, Gillman contends buying mantises or their egg casings for that purpose is just a waste of money, because individual mantises don't eat nearly enough insect pests to protect one's crops. I used to sing the praises of manure and compost teas, too, but, while both deliver some nutrients, they can potentially spread harmful pathogens such as E. coli.

Now I was at least dimly aware that even though a particular pesticide might sport the word "organic" on its container, that doesn't mean that it is especially safe. Gillman drives the point home with details on different products' Environmental Impact Quotients (EIQ) -- a complicated measure of a compound's risk to farm workers, consumers, and the environment.

A high EIQ score -- of 100 or so -- indicates the pesticide in question is potentially very harmful, while a lower EIQ -- around 10, perhaps -- poses less danger to its human handlers, beneficial insects, and the ecosystem. Consider Rotenone for a moment. Yes, it's organic, but it has an EIQ of 33 and is quite toxic to fish. (For a point of reference, you can download EIQ values for over 200 commonly used pesticides.) In comparison, the very popular, synthetic pesticide Sevin has an EIQ of 20.9. 

All-natural, Chrysanthemum-derived Pyrethrum may also seem relatively innocuous to the organic gardeners choosing to use it, but its compounds rate an EIQ of 18. The ubiquitous synthetic Roundup is a 15.3. Of course, there is more to a pesticide than its EIQ; after all, Gillman acknowledges, pyrethrins do break down rapidly. . .

Like it or not, there aren't always easy answers for gardeners looking to lower their impact on the environment. All in all, this Timber Press book is a thought-provoking eye-opener.

Story by Susan Brackney. This article originally appeared in Plenty in January 2008.

Copyright Environ Press 2008

The truth about organic gardening
Find out what really makes your garden "organic".