See the presentation at the bottom.
Benefits of Rock Dusts
Glaciation & Vulcanization
- Increase the variety of minerals available to microbes and, eventually, to plants. There are only 18 nutrients considered Essential to plant life. Nickel was only recently added in 2004. But what about beneficial? Iodide & selenium, among others, are now considered beneficial to plant life. As for other elements, we just don’t know what we don’t know.
- Provide a more consistent source of minerals to plants.
- Will not burn plants or harm microbes.
- Increase cation & anion exchange capacity.
- Increase paramagnetism.
- Increase moisture retention.
- Improve soil structure.
- Improve drainage.
Cons of Rock Dusts
- Requires microbial life to unlock the minerals.
- Requires sugars from well-photosynthesizing healthy plants to feed microbes.
- Soil tilling can set back the mineralization process.
- Can take some time to become effective.
- Improper use can choke the soil.
- May be unnecessary in some areas.
- Ineffective in high concentrations of salt fertilizers.
- Can be a challenge to be effective in container growing.
Examples of Rock Dust
I use all of these:
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 (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.
DE loosens soil and is a good source of micronized Silicon in the form of 80-90% Silica.
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.
- Super Greensand – Powder on Amazon
- Super Greensand – Micronized on Amazon
- Super Greensand – Granular on Amazon
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 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:
- Calcitic – contains very little magnesium, breaks down and adjusts pH quickly.
- Calcitic Lime on Amazon
- Dolomitic – contains higher levels of magnesium, breaks down more slowly, adjusts pH more slowly, but has a much longer effect.
- Dolomitic Lime on Amazon
Mined from an ancient volcanic ash bed, contains 0.2% available potassium and many micronutrients.
- Leonardite is often the raw source of humic and fulvic acids, but also includes the important humin component, which is removed through the refinement process to produce humic and fulvic acids.
- Caution should be used when applying leonardite, as it can chelate, complex, and bind up nutrients in the soil. Think of leonardite as a light nutrient magnate and the rock dusts as super strong magnates.
- Leonardite is not soluble in water, but will mix well in suspension. A small amount of yukka extract will help with the mixing process, but is not required.
- Leonardite on Amazon
- Nectar for the Gods Yukka extract on Amazon
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
- Some micronized rock dusts can be applied through irrigation lines.
- Some small rock dusts can be stirred into solution and administered with a watering can, but would be too large to go through many irrigation systems without clogging.
- The smaller the particle size, the more surface area will be available to the microbes.
- Small particle sizes act quickly and more intensely, but are soon used up.
Larger Rock Dusts
- Larger particle rock dusts will need to be directly applied to the soil surface.
- The larger the particle size, the less surface area will be available to the microbes.
- Larger particle sizes will not have quite the effect of smaller particle sizes, but will last longer.
Pelletized Rock Dusts
Pelletized rock dusts reduce dust levels, but may not mix as well as some of the finer rock dusts.
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.
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.
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 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.
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 should be avoided when possible.
- Tilling disrupts the microbial life needed to mineralize the rock dusts.
- Tilling oxidizes the nutrients already available in the soil, making them less available to plants.
- Let the worms work for you.
Avoid Peat Moss
I’m not sure what it is about peat moss, but microbes, especially mycorrhizal fungi, do not seam to like it.