What Works (and What Doesn't) in Gardening

A horticulturist debunks some popular gardening remedies and suggests the ones that actually work.

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by Marie Hofer, Gardening editor, HGTV.com

Hot-pepper spray to get rid of insects, gravel in the bottom of containers to aid drainage, eggshells to stop slugs — the world of gardening overflows with home remedies. Many gardeners usually love to try the natural approach, believing that solutions fashioned from nature — or the average kitchen — are just as effective as commercial fixes, and if they fail, no harm is done.

Jeff Gillman has tested the theories. His search for what works in the garden began with a question from a gardener about a homemade pest remedy. His graduate degrees in entomology and horticulture and a brand-new PhD couldn't help him answer the question, and he set out to find the answer — by testing the remedy himself.

In fact, there were many such questions, and Gillman, an associate horticulture professor and nursery manager at the University of Minnesota, began his simple experiments. For the eggshell-slug question, he lined the outside perimeters of paper plates with crushed eggshells and put slugs in the center to see how long it would take for them to cross the eggshells and exit the plate (nearby, his wife made lime pies with the contents of the eggs). The slugs left the plates so fast that Gillman worried he hadn't crushed the shells enough. So he crushed more eggshells (still more pies to make, we gather). He found that the most effective strategy was a quarter-inch-thick layer of moderately crushed eggshells but that only slowed the snails and didn't turn them off. "That is not to say the slugs were reluctant because they weren't," he wrote, "but they had a tougher time getting through the shells."

What did work, Gillman tested, was diatomaceous earth. The slugs "quite clearly hated the stuff."

The Truth About Garden Remedies (Timber Press, 2006) debunks many myths (gravel in the bottom of containers) and verifies the truth about others (hot pepper spray and garlic, to name a few). Each remedy is presented with the practice, the theory behind it, the real story (his experiments and their results) and a summary called "What It Means to You," and a recommendation of anywhere from one to five flowers.

Earning three flowers was mouthwash, sometimes recommended as a fungicide. Gillman found that when diluted 4:1 with water, mouthwash beat out every other homemade remedy as a treatment for blackspot and powdery mildew, although it still wasn't as good as the commercial fungicides.

"Mouthwash surprised me to no end," Gillman says, but cautions care. "It can cause burning of the leaves so you have to be careful."

No matter which side of the natural-and-homemade fence you prefer, you will find this book useful. Gillman takes the uncertainty out of the remedies and explains the science behind their success (or lack of it). You'll have to read the book for the rest of the advice.

And he still has plenty more remedies to try. "Borax for creeping charlie--I can't believe I didn't do that one," he laughs. "And isopropyl alcohol for mites — that's a great one that just fell through the cracks."

Stay tuned.

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