See the presentation at the bottom.

Benefits of Rock Dusts

Glaciation & Vulcanization

Extent of Glaciations

Cons of Rock Dusts

Examples of Rock Dust

I use all of these:

Basalt

Basalt is a lava rock that is high and broad in many trace minerals. It also resists weathering and has the highest paramagnetism of any of the rock dusts.

Gypsum

Gypsum (calcium sulfate) includes the macronutrients Calcium (22.5%) and Sulfur (18%), loosens soil, increases stable organic matter, increases earthworms, reduces carbon volatility, increases amino acid production, and improves root penetration. Unlike alkaline lime or acidic sulfur, gypsum is pH neutral.

Diatomaceous Earth

DE loosens soil and is a good source of micronized Silicon in the form of 80-90% Silica.

Greensand

Greensand is sandstone formed from fossilized marine life. It contains 70 minerals and trace elements, including potassium, iron, magnesium, and manganese. The Brazilian source contains 0.2% readily available and 10% total potassium.

Rock Phosphate

Rock phosphate contains high levels of phosphorus, but the amounts can vary widely, depending upon the source. The Epsoma brand contains 3% available, 32% total phosphorus.

Agricultural Lime

Agricultural lime is a form of crushed and powdered limestone that has NOT been kiln-fired. Kiln-fired limestone is often used in mortar and concrete, and is very caustic. Ag lime is often used to raise the pH of acidic soils. It is also a source of calcium (calcium carbonate) and magnesium (magnesium carbonate). On acidic soils it can improve water penetration and increase nitrogen, phosphorus and potassium plant uptake.

There are two categories of ag lime:

Azomite

Mined from an ancient volcanic ash bed, contains 0.2% available potassium and many micronutrients.

Leonardite

Rock Dust Application

Wear a Dust Mask

It’s called rock dust for a reason.

Particle Size Matters

Should I use micronized, powdered, pulverized or pelletized?

Finer Rock Dusts

Larger Rock Dusts

Pelletized Rock Dusts

Pelletized rock dusts reduce dust levels, but may not mix as well as some of the finer rock dusts.

Application Rates

Follow the package recommendations, except for leonardite and lime. It is better to dish out smaller amounts over time, as leaonardite and lime will tend to bind up nutrients.

Application Timing

Apply all rock dusts in the fall, after dormancy, to allow the rock dusts to be “digested” by the soil over winter. This is especially important for leonardite and lime. Gypsum and rock phosphate can be reapplied in the spring. Green sand can be reapplied at the flower/fruit-set stage for additional potassium. If you have never applied rock dusts to your soil and it is not yet fall, you can apply a small amount to get the minerals into your soil, then follow up with the fall application.

Mulching

Applying mulch and/or compost over the rock dusts will assist in its being metabolized into the soil by microbes and worms, and keep the rock dusts from caking on top of the soil.

Watering

Watering in with a mixture of microbial inoculants, sugar and cold processed kelp will super charge the process. If I have plants growing that I don’t want to choke with mulch, watering the rock dust into the soil can help keep it from caking and make it more accessible to the microbes and worms.

Mixing

For container soil or in-ground soil amending, using a cement mixer to mix soil, fertilizers, rock dusts and inoculants is much easier and thorough than mixing by hand. Small batches can easily be mixed by hand.

Tilling

Avoid Peat Moss

I’m not sure what it is about peat moss, but microbes, especially mycorrhizal fungi, do not seam to like it.

Additional Rock Dust Educational Resources

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