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The great gardening debate: organic vs. chemical

Imagine a political debate in which a moderator could take apart the campaign promises and reveal, with Solomonic wisdom, their true benefits, drawbacks and costs.

Enter Jeff Gillman, a professor of horticulture, who is passing judgment not on the current presidential race but on an even longer-running contest: the pros and cons of organic vs. chemical gardening.

Gillman has spent years poring over scientific data to scrutinize the claims of the organic gardening movement in an attempt to give objective assessments of hundreds of products and practices.

This is not ivory tower stuff; all gardeners are faced with this vexing choice. Plants need feeding; plants get sick or get eaten.

Anyone who has haunted garden centers and mass merchandisers for many years can see there has been a profound shift in consumer demand away from the stinky chemical herbicides and pesticides that once monopolized the shelves and toward organic controls, fertilizers and soil mixes.

Trying to find definitive, impartial advice is hard. At its extreme, organic gardening isn't so much a practice as a religion, whose true believers view chemicals (and the people who make them) as devilish and assert that natural controls will keep plants healthy and the environment safe, including you. On the other side, advocates point out that chemical, or more correctly, synthetic fertilizers and pesticides are as safe as they are effective.

Confusing the issue is the fact that eco-friendly claims are a huge part of every sales pitch these days. How do you separate the hype from the facts? Spending 13 bucks on Gillman's new book, The Truth About Organic Gardening (Timber Press), may go a long way.

From the ground up

But first we need to take a step back. Gillman's fundamental argument is that if you are simply replacing synthetic products with organic ones, you are missing the point. The aim is to reduce the need for fertilizers and, especially, pesticides. How do you do that?

You build the soil with correct amounts of compost and mulch, choose plants that do well and place them in their optimum locations. "These are the true parts of organic gardening," says Gillman, a professor of horticultural science at the University of Minnesota.

In writing the book, Gillman says, he wanted to point out something that is probably not well understood: that organic products can be as harmful as synthetics, or even more so.

Not necessarily safe

Rotenone is an organic dust that gardeners place on potato plants, for example, to kill the destructive Colorado beetle. The plant-derived insecticide is highly toxic to aquatic life, and when low doses were injected into rats, they caused symptoms similar to those of Parkinson's disease. "Why would any sane person use this pesticide?" Gillman writes.

Neem oil is derived from a South American tree species. You pour a small amount of it into a gallon or two of water — the liquid turns milky and smells a little acrid — and you spray plants that are being attacked by such things as aphids, leaf hoppers and mites. It also doubles as a fungicide. It seems like the perfect alternative to synthetic and toxic rose sprays, for example. Gillman's verdict: effective as an insecticide, less so as a fungicide, and destructive to aquatic life. In addition, it has been linked to reproductive defects in rats and, if not processed correctly, may contain a carcinogen called aflatoxin. He writes he is "somewhat hesitant about using it."

In an interview, Gillman tells of coming across a woman with severe circulatory disorders in her hands. She was grossly overdosing indoor plants with neem oil, and he suspected a link. "Generally it's safe," he says. "But (as) with any pesticide, applying it again and again can have terrible effects on the human body."

Moderation is key

Organic gardeners rail against synthetic fertilizers for the destructive effect of their salts on beneficial soil creatures and soil structure. Gillman says the only real problem occurs if the synthetics are applied too frequently. "For a garden (as opposed to a farm), I would rather use organic fertilizers, but if you're using synthetics once or twice a year, that's fine," he says. Four or five applications, however, would be "nuts."

One of the hottest things in organic gardening is compost tea, a soup you make by percolating water through a sock filled with natural nutrients and compost. The resulting liquid is teeming with beneficial bacteria and fungi that are then sprayed on plants to feed and protect them. Gillman says the soil is already full of such microbes. The apparent vigor of plants sprayed with compost tea is simply a response to the nutrients taken up by the leaves. There is also a risk of brewing dangerous E. coli germs. And given the time and labor involved, Gillman says, the gardener is better off making a basic foliar spray. You could use liquefied seaweed, for example.

His book touches briefly on the omnipresent lawn and yard care services.

"I don't like yard care companies in general," he says. "They use too many chemicals too often." He urges consumers who use them to know exactly what is being applied and for what purpose, and to veto specific applications if necessary: "What's wrong with having a few dandelions in your yard?"

Gillman writes that by presenting various practices and chemicals in an objective light, he hopes he can help readers make up their own minds "without the extreme biases" on either side of the issue.

"I don't know whether it will change people's minds," Gillman says. "I want the book to, at least, start the conversation."

The great gardening debate: organic vs. chemical 03/21/08 [Last modified: Thursday, October 28, 2010 9:44am]

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