Rock Dust in the Soil

Posted by Aaron 23/03/2018 0 Comment(s)

Glacial Rock Dust 

The last glacial age (a period of time within an ice age), and the only one to occur since humans appeared began 1.5 million years ago and receded 15,000 years ago. During that time the Laurentide ice field covered all of Canada and extended as far south as Indiana. Once receded, it left behind a bed of pulverized rock dust, up to three meters thick in some places, forming much of the mineral base of north American soils, rich in elements.

This process has renewed the mineral content of soils in much of the northern hemisphere and is why Russia, Europe and North American soils generally have had a good mineral content. They were rich and deep and farmers had the benefit to go on farming them year after year. Soils close to the equator where the glacial re-mineralization process has not occur missed out, hence are generally deficient in minerals such as, phosphorus, copper, zinc, molybdenum, cobalt, and sulfur, as is the case with Australian soils.

Why Rock Dust?

Rock Dust is widely used in gardening and farming because it returns minerals to soils that have been lost due to overgrazing, leaching, urban and rural development or soil erosion. Rock dust increases the soil’s moisture holding capacity, improves soil structure, drainage and the soil’s ability to release nutrients by increasing rates of cation exchange.


While Rock Dust has many advantages, it should not be considered a stand alone fertilizer because it lacks the necessary amounts of phosphorous, potassium, and nitrogen to maintain good soil health. Further, Rock Dust products have a varying mineral content depending on the type of rock they came from. For example, Limestone has low levels of micro nutrients and minerals, whereas granite and igneous rock basalts have a high mineral content. Research shows that adding Rock Dust to farms, gardens and potting soils increases fertility and corrects many nutrient deficiencies.


A good Rock Dust should contain a diversity of minerals, volcanic materials and rich glacial sediments. For example, Basalts and Glacial sands are a good mix. Granite is a popular form and is often used because of its known potassium content and is widely available as a by product of quarrying. Also, Rock Dust that contains the remnants of living creatures such as algae, diatoms and crustaceans are high in calcium and magnesium carbonates. Like most good natural systems Rock Dust is about diversity, the best Rock Dusts provide a range of minerals (70+) that you can distribute evenly throughout your growing media. I get a trailer load of crusher dust from a quarry nearby, which is a mix of fine powdered granite and up to 1mm particle size. It costs about $50 (aus) and is normally used as an underlay for concrete footings, most raw material suppliers should have it. I've found it helps with drainage in my clay soil, particularly around my fruit trees.


  • improves drainage
  • improves soil structure
  • increases the soil’s moisture holding capacity
  • increases the soil’s ability to release nutrients by increasing rates of cation exchange

Microbes will release the Minerals from Rock Dust

Healthy soils are teaming with life and for every gram of soil there is roughly 1 billion micro-organisms. They are incredible diverse containing  bacteria, fungi, protozoa, and viruses. One handful of soil can contain tens of thousands of different species of microbes which provide food for earthworms, nematodes, arthropods, plants and each other. The abundance, diversity and  the recycling of nutrients and minerals microbes provide is the key to any healthy soil. However this is not a closed system and what we take out we must put back in to maintain the health and diversity of the soil life.


By adding Rock Dust to soil you ensure the soil food web can sustain robust microbe populations; which release minerals around the plants roots. Also, microbes respire producing carbon dioxide that dissolves in water, producing carbonic acid. This mild acid acts as a gentle weathering agent releasing minerals, particularly potassium.


The Science of Soil Health: Nature's Way of Extracting Minerals from Soil source: youtube


Use compost, worm castings. Compost Tea and Mycorrhizae directly with your Rock Dust as they will help facilitate the production of carbonic acid. Further, new research suggests that by encouraging the soil microbial life, we revitalize and accelerate soil regeneration, way beyond normal rates seen in nature.


Rock Dust in your Compost

Creating compost with rock dust is a good way to incorporate the minerals within the microbial network of your compost, making the nutrients readily available to your plants once you apply the compost. Azomite is a popular, convenient Rock Dust product which can be added to your compost. Add 2 to 20 pounds (0.9 - 9 kg) per cubic yard (0.77 cubic meters) of compost. Adding your local soil to your compost is highly recommended, as your local microbes have adapted to your climate conditions, so they will be well suited to your compost pile. The finer the Rock Dust powder the easier it is for the microbes to use it. It should feel soft like flour or talcum power. Microbes really love Rock Dust and consume it easily; and they do this particularly well!

How to Use in the Garden:

Dust lightly for Dry Applications and if possible turn in to the soil on new plantings:

Potted Plants:

  •     Use 1-2 teaspoons per 1 gallon (3.8 liters) pot size
  •     Use a high quality Potting Soil

Fruit Trees:

  •     Broadcast around center canopy and beyond the drip line
  •     At the rate of 1 lb (0.45 kg) per 100 sq ft or (9.3 m)

For Vegetables, Flowers, Lawns, Ground Covers and Shrubs:

  •     Apply 1-2 times per year
  •     Apply at every new planting
  •     10 lbs (4.5kg) per 1000 sq ft. (93 sq m)


Whether you use Rock Dust to fertilize your plants or as an addition to your compost, it is a fantastic way to help your garden achieve higher yields and increase vigor and resilience in your garden. Try the combination of Rock Dust, Mealworm Castings, Kelp, Great White Mycorrhizae and Alfalfa for a good all round fertilizer regime.


Thanks for reading the blog! If you like this article please like and share. Also, theres high quality Alfalfa Meal, Organic Amendments and Mycorrhizae for the garden, I’ve found the Cyco Ryzofuel, and the Worm Castings work extraordinary well. And Happy Gardening!