Rock Dust: The Secret to Healthier Plants and Soil
Organic farmer Bob Cannard, known for growing 10-pound beets and carrots for a juice company and gourmet restaurants, shares his secret to large, mouthwatering produce: rock dust.
Cannard has used 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. According to him, rock dust is a natural, effective way to nourish plants.
What is Rock Dust?
Rock dust, found in nature, is a byproduct of the gravel industry. In places like Orange County, gardeners often use gypsum, a type of rock dust made of calcium and sulfur, to help neutralize alkaline soil. Many believe that rock dust ground naturally by glaciers or rivers is the best option due to its wide range of minerals from various stones.
The Benefits of Rock Dust
Here’s why rock dust is considered an essential soil amendment:
- Improves Soil Health: Plants are healthier and more disease-resistant in soil re-mineralized with rock dust.
- Better Taste: Fruits and vegetables grown with rock dust are said to taste better.
- Loosens Clay Soil: Rock dust helps to break down dense clay soil, improving its structure.
- Long-Term Soil Benefits: Unlike chemical fertilizers, rock dust is a slow-release amendment that provides nutrients for months.
Cannard explains, “I wouldn’t be a farmer today if I didn’t use rock dust. 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.”
Rock Dust vs. Traditional Fertilizers
Unlike soluble chemical fertilizers that provide an instant nutrient boost but quickly leach away, rock dust works over time, continuously enriching the soil. Plant pathologist David Miller states that rock dust increases the microbe level in the soil, helping plants absorb more minerals.
R.J. Schwichtenberg of Hummingbird Landscape Care compares rock dust to whole wheat bread versus white bread. “Rock dust is a more complete product that is naturally integrated into the soil. In contrast, chemical fertilizers leave behind harmful salts that can damage the soil.”
Microbe Activity in Healthy Soil
Soil microbes, such as mites, nematodes, and worms, thrive in high-mineral environments. When these microbes die and decompose, they release minerals in a form easily absorbed by plants. According to Walt Zmed of Earth Wealth, “Rock dust feeds the microbes, which helps build soil fertility and prevent erosion.” Zmed believes that using rock dust benefits both your garden and the earth.
Real-World Success with Rock Dust
Santa Barbara organic farmer John Givens has also seen positive results using rock dust on his farm. “We’ve used it since 1987 and have been able to grow a variety of crops on land that was once difficult to farm,” he says.
Availability of Rock Dust
While rock dust is hard to find in local nurseries, it is available through mail-order companies. A 20-pound bag costs as little as $6.50, covering about 50 square feet. Experts recommend adding generous amounts of rock dust for the first two to three years, then switching to annual maintenance. For example, a mature rose bush needs 3-4 pounds per year, while a mature tree requires 8-10 pounds annually.
The Historical Background of Rock Dust
The benefits of rock dust have been recognized for over a century. In the 1890s, American chemist Julius Hensel published the book Bread from Stones, which promoted rock dust as a way to enrich the soil. Interest in rock dust revived in the 1970s, and today, it is used by a growing number of home gardeners and organic farmers.
