Rock dust – also sometimes called basalt rock dust – is a valuable input in organic gardening. The material’s use goes back thousands of years, but it remains helpful today, complementing modern techniques. 

This post explores basalt rock dust as a soil improver. We look at what it is, how it works, the benefits of using it, and how to use it in your application. After that, we take a quick look at some case studies of people using it successfully to promote growth.

What is Rock Dust?

So, what is rock dust?

Basalt rock dust comes from basalt (as the name implies), supplying plants with a steady stream of nutrients over time. As an igneous rock, it originally emerged from volcanic eruptions, later being found to promote crop health and vitality.

Unlike many other rocks, basalt contains the correct balance of chemical elements to support plants through various stages of growth development. Analysis of the material shows it is high in silica (44%), iron oxide (11%), and calcium oxide (9%), with trace elements comprising the remainder. Many soils are deficient in these compounds, making the material extremely helpful in multiple facets of plant growth. 

Furthermore, research suggests basalt rock dust increases the availability of other elements plants require to construct their tissues, including phosphorus, potassium, and magnesium. Application of the material can increase soil levels multiple times with proper incubation. 

Most basalt rock dust is a byproduct of mining and quarrying. Miners often remove the rock when looking for other materials, selling it to secondary processors for crushing and pulverizing. Occasionally, miners deliberately dig it up for agricultural purposes, crushing it into fine powder using gigantic roller or hammer mills. 

Benefits of Using Rock Dust

The benefits of using rock dust in gardens (regardless of what you want to grow, and along with other beneficial amendments) are substantial. The substance is exactly what you need to create a backyard worthy of showing off to friends and neighbors. 

Improved Fertility And Soil Remineralization

The chief benefit is rock dust’s ability to improve fertility. Adding magnesium, iron, phosphate and calcium to the soil provides plants with the raw ingredients they need to flourish. 

Some evidence also suggests adding rock dust to soil can improve microbe biodiversity. The material appears to promote the growth of carbon-sequestering bacteria with most positive effects arising three years after initial treatment. More diverse soils with extra bugs are healthier and more sustainable, reducing degradation and making topsoils less susceptible to surface run-off.

Better Plant Health And Growth

Improved soil fertility also leads to better health and growth. The presence of additional minerals can assist plants by: 

• Thickening stems and making them more robust to insect invasion
• Improving enzyme production
• Enabling photosynthesis
• Regulating plant hormones
• Reducing the ability of invading fungi, such as Pythium and powdery mildew to take hold
• Increasing resistance to heat and drought
• Contributing to the production of heavier fruits, vegetables, and flowers

Improved Soil Structure

Beneath the ground, adding rock dust can also improve soil structure through various channels. Better cation exchange capacity allows it to retain more plant nutrients for longer. 

Furthermore, roots may grow thicker and deeper. These additional structures help to hold soil in place and reduce the risk of degradation via weathering. 

Reduce Reliance On Chemical Fertilizer

Another benefit of rock dust is reduced reliance on expensive chemical fertilizers. While you still need nitrogen, basalt rock dust can contain significant quantities of phosphorus and potassium, making it an excellent option for promoting plant growth without choosing synthetic options. 

Furthermore, rock dust contains countless micronutrients, including zinc, copper, boron, molybdenum, and manganese. Many garden species require all of these to thrive. 

Boosting the Benefits of Basalt Rock Dust with Worm Castings

Many people believe that rock dust alone doesn’t work, but this is often because their soil lacks the necessary biological activity. Using worm castings along with basalt rock dust creates a rich, active soil environment that maximizes the benefits of both. The microbes in worm castings help break down the minerals in basalt rock dust, making nutrients like magnesium, calcium, and iron more accessible to plants. This combination ensures that the nutrients in rock dust are fully utilized, leading to healthier plants.

How to Apply Rock Dust

These benefits sound fantastic, but how do you apply basalt rock dust? Should you dump it on your soil, or does it require a careful approach? 

Step 1: Choose Your Rock Dust

Generic “rock dust” (random ground-up stones) won’t fertilize your plants and may worsen soil quality. Therefore, double-check the packaging to ensure it is basalt rock and suitable for garden applications. We pride ourselves on providing high quality basalt rock dust to our customers.

Step 2: Choose The Location

The next step is to choose where you will apply the rock dust. Spreading it everywhere is okay, but over-mineralizing plants can be dangerous (and costly). 

Therefore, look for areas in your garden that require the most rock dust. These could include patches with sickly plants or areas that failed to flower or produce a sufficient crop in the past. 

Step 3: Apply A Top Dressing

Next, apply a “top dressing” to the target soil. Here, you have two options: 

• Sprinkle the rock on top of the soil
• Sprinkle the soil and then rake

Most people choose the first option – it’s easy and weather/rain will eventually cause it to mix into the ground below. However, if you don’t have plants growing in the immediate vicinity, raking can help fertilize the soil faster. 

Use a lime spreader or fertilizer spinner for large areas, but be careful: these machines can overspread easily if you don’t drive them fast enough. 

Step 4: Wait For The Magic To Happen

The last step is to wait for the magic to happen. You should notice plants begin to look more robust and grow better once they have the nutrients they need. 

Some finer basalt particles break down improving soil health and drainage after a few weeks. Then after several months or years, the larger rock dust particles begin to incorporate into the soil, leading to higher yields and CO2 capture. 

Most gardeners reapply rock dust every three to five years because of how long it takes to release. However, you don’t really know if you have enough unless you do soil testing. Checking its mineral composition can provide more insights into what it needs.

Case Studies

Are you wondering if using basalt rock dust really works, even in the sandy soil of Florida? Studies and tests on the effectiveness of basalt rock dust on soil remineralization are few and far between, but there are several studies from various places around the globe that give us an idea of its effectiveness, no matter where you live.

Fritz Leipold Study in Siegkreises, Germany

Garden landscape consultant Fritz Leipold was the head of the Department for Tree Nurseries and Landscaping at the Research Training Institute, and now Technical College in Weihenstephan, teaching about vegetable growth since 1948. He tested soil remineralization using basalt rock dust on a sandy 2.5-hectare plot. Between 1949 and 1952, he applied the dust as a fertilizer to the soil to see if it would have an effect. The application increased the pH and added key elements to the mixture, contributing to the development of the first plants. 

At the end of the experiment, Leipold and his group could grow numerous plants on the land, including apple trees, strawberries, and tomatoes. The land continued to be improved and eventually, the soil grew several feet thick, allowing the production of grain and other crops requiring enriched soil for optimal yields. 

Lucas Terto Conceição Study In Brazil

Lucas Terto Conceição and a Brazilian team conducted a similar study in Brazil, looking for a way to improve crop management and soil fertility in a part of the globe prone to degradation. The group from the Federal Institute of Mato Grosso do Sul and Mineragro Pesquisa e Desenvolvimento wanted to see if basalt rock dust could improve sandy and dry soils, permitting plant growth. 

The team incubated soils with dust doses for 90 days and analyzed their chemical properties. Then, they added maize and bean plants, evaluating their shoots for dry weight and nutrient composition. 

The study showed basalt dust increased phosphorus, potassium, calcium, and magnesium availability significantly because of increased soil concentrations. Maize and bean plants grew in marginal environments, paving the way for agriculture to expand into unused regions. 

Steven Banwart Study in Leeds, UK

Lastly, a team from Sheffield and Leeds Universities including Professor Steven Banwart, found that finely crushed basalt can boost soil CO2 sequestration – something eco-conscious gardeners might be interested in. The material could contribute to removing between 6 and 30 million tonnes of CO2 from the atmosphere every year – a requirement for the UK to meet its net zero targets by 2050.

Conclusion

In summary, basalt rock dust is a potent tool for improving the fertility and structure of soils, especially in organic gardening. Its application can lead to healthier plant growth, better soil structure, and increased resistance to environmental stresses. Additionally, it can contribute to environmental sustainability through enhanced carbon sequestration. However, its effectiveness is maximized when used as part of an integrated soil fertility management plan that includes regular soil testing and organic matter additions. With proper application, basalt rock dust can transform marginal soils into productive gardens, as evidenced by various global case studies.

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