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Dusting Off a Tip, Gardeners Get a Piece of the Rocks


Organic farmer Bob Cannard grows 10-pound beets and carrots for a juice company and a gourmet restaurant. Ask him his secret to large, mouthwatering produce and his answer is simple: rock dust.

Cannard has used nothing but ground-up rock and compost on his plants for 25 years. He applies no other fertilizers and never uses pesticides on his 136 acres of farmland in Sonoma.

Rock dust is found in nature and is also a byproduct of the gravel industry. Many gardeners in Orange County re-mineralize their gardens with gypsum--a rock dust made of calcium and sulfur that helps to neutralize alkaline soil.

Although almost any ground rock is a good addition to the garden, growers such as Cannard believe that adding rock dust ground naturally and mixed by a glacier or river is best because it contains a wider range of minerals from a variety of stones.

Plants are healthier and more disease resistant when the soil is re-mineralized, say rock-dust supporters. Fruits and vegetables fertilized with rock dust taste better, experts say, and rock dust helps to loosen clay soil typically found here.

"I wouldn't be a farmer today if I didn't use rock dust," Cannard says. "It's important to build the soil, because you can't grow high-life plants out of low-life soil. Thanks to the rock dust, my plants have a good mineral supply. They're strong and healthy and are never bothered by bugs."

Although soil is primarily composed of pulverized rock, years of supporting plant life depletes most of the minerals and nutrients, says plant pathologist David Miller, an associate professor at Oberlin College in Ohio.

Standard fertilizers of nitrogen, phosphorus and potassium don't contain micronutrients that plants need to thrive.

R.J. Schwichtenberg of Hummingbird Landscape Care in Orange likens the use of rock dust versus traditional chemical fertilizers to eating wheat bread instead of white.

"Rock dust is a more whole product that is sustaining and more satisfying," says Schwichtenberg, who sells organic food directly to clubs and co-ops. "Rock dust is naturally integrated into the soil. . . . Chemical fertilizers . . . leave behind a high ratio of salts, which can be damaging to the soil."

Unlike soluble chemical fertilizers that give plants a rush of food and then leach away, rock dust is a slow-release amendment that will continue to work for months.

Plant pathologist Miller has been studying soil amended by rock dust, as well as the nutrient level of plants grown in such amended soil, for six years.

"We've seen evidence that rock dust makes vegetables more nutritious," Miller says. "It definitely increases the microbe level in the soil, which means that more minerals are passed to the plants."

Soil microbes such as mites, nematodes, worms and other small insects thrive in a high-mineral environment. Once they die and decay, they release minerals in a form readily available to plants.

When it comes to soil health, concentrate on the unseen world of microbes, says Walt Zmed, owner of Earth Wealth, a mail-order company in Canoga Park that sells rock dust.

"Rock dust feeds the microbes, which helps to build soil fertility and stop erosion," says Zmed, who has been gardening for 30 years and started using rock dust six years ago. "By using rock dust, you not only improve your landscape, you also do something good for the earth."

Santa Barbara organic farmer John Givens has also had luck with the mineral-rich powder on one parcel of his 150 acres.

"We've used the dust since 1987 and have been able to grow a variety of vegetable crops on land that was difficult to farm," he says.

OK, now the bad news.

It's difficult to find.

Armstrong's Home and Garden Place in West Los Angeles is one of the few sources in the Southland.

"Rock dust sells out really quickly when we get it in," says assistant indoor garden manager Peter Crist.

Although rock dust is hard to find in the nursery, mail-order companies sell it. Bagged rock dust costs as little as $6.50 for a 20-pound bag, which will cover about 50 square feet.

Because most soils have been greatly depleted of minerals, experts suggest adding generous amounts of rock dust for the first two or three years, then switching to yearly maintenance. A mature rose bush would take three to four pounds a year, while a mature tree would require about eight to 10 pounds a year, Zmed says.


In the 1890s, American chemist Julius Hensel wrote the book "Bread From Stones," which covered the benefits of using rock dust on plants.

Don Weaver, author of the book "Survival of Civilization," which focuses on the use of rock dust to regenerate the soil and forestall the next Ice Age, discovered rock dust in the late 1970s.

Interest grew in the United States 25 years ago, and rock dust is now used by a small, growing number of home gardeners and organic farmers.

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