Volcanic Rock Dust: How Much Should I Use in my Garden?

“How much should I use?” is probably the most frequently asked question that we receive from first-time users of volcanic rock dust. Naturally, most people are concerned about any potential dangers associated with overuse.

We cannot speak for other brands, but we can give you some practical advice for using Cascade Minerals Remineralizing Soil Booster which is made entirely of volcanic basalt rock. Containing absolutely no synthetic materials, it is listed for use in organic production by the Organic Materials Review Institute (OMRI).

There are two other things to keep in mind regarding the question of “How much?” The first is solubility. The other is porosity, or structure.

First, volcanic basalt is relatively low in solubility. The same cannot be said of man-made fertilizers which are highly soluble. It is this highly soluble nature of synthetic fertilizers that makes them such a liability if they are over-applied or misapplied. Excessive nutrient levels or poorly timed applications can result in injury to plants, contamination of the environment, and/or loss on investment.

Because volcanic basalt is so much lower in solubility—and because of its natural balance of nutrients—the risks of injuring plants or the environment are non-existent in comparison.

The second is porosity, or structure. Plant roots need to be able to breathe and drink while obtaining the nutrients needed for growth. The porosity and structure of a rooting media determines root productivity. For example, if you took a bag of ground basalt and just added seeds and water the outcome would be disappointing because the roots wouldn’t have enough air to breathe.

The same effect is likely to happen if you cover your plants with 1-2 inches of rock dust with little or no incorporation into the surrounding soil. The volcanic material would likely suffocate the roots and soil. (Farmers that experience deposits of volcanic ash have to incorporate the ash into their existing soil because the ash itself lacks the structure for roots to thrive.  The deeper the ash deposit, the deeper a farmer must plow to achieve the right mix.)

In short, when applied as directed and incorporated into the soil, there should be little to no fear about over-applying Cascade Minerals Remineralizing Soil Booster. On the other hand, more is not necessarily better. Once a sufficient dose of volcanic rock dust has been applied to produce a beneficial plant response, adding more minerals is not likely to increase the magnitude of the response during the growing season.

Here is a video in which agronomist Rich Affeldt talks about the versatility of Cascade Minerals Remineralizing Soil Booster and addresses common questions about application rates and how much product to apply to gardens, lawns and containers to ensure healthy and vigorous plant growth.