The Slow-Release Benefits of Basalt

By releasing essential minerals and nutrients, rock deposits are essential to healthy plant growth and increased agricultural yields. However, not all rock amendment products are alike. For balancing overall soil health, basalt stands out from other rock materials.

Created through the cooling and solidification of magma and lava, basalt is the rock material that makes up most of the soils around the world. Compared to other volcanic rocks that are high in quartz, basalt weathers relatively quickly.

It begins to release nutrients to plants as soon as the roots make contact. Additional nutrients become available with ongoing decomposition, thereby resulting in a steady flow of nutrients over time.

Using volcanic basalt powder (often referred to as rock dust) as a soil amendment is not new. In the 1930s, researchers in Europe used finely ground basalt to treat and improve the productivity of degraded forest lands.

One of the most comprehensive studies on the benefits of crushed basalt came from D. Hotman de Villiers, who conducted a series of long-term field trials on highly degraded soil that led to increased sugarcane yields on the Island of Mauritius.

The tests started as early as 1937 and resumed in the 1940s and 1950s at the Sugar Cane Research Station of Mauritius. Scientists commenting on de Villiers’s work note several reasons behind basalt’s effectiveness as a soil amendment, including improved silicon nutrition, enhanced trace element supply, alteration of the soil’s physical properties and modification of mycorrhizal populations.

Further studies have shown that a major mechanism influencing positive crop response on highly weathered soil is basalt powder’s ability to increase soil function and productivity as measured by cation exchange capacity.

Today, scientists across the globe continue to research the benefits of basalt. While plant species vary widely in their nutritional requirements, volcanic basalt is proven to improve root systems, increase yields and promote general plant health in a wide variety of crops and conditions—including those in indoor growing situations, where mineral deficiency can be an issue.

As the byproduct of violent volcanic activity, basalt is not an amendment that indoor growers may associate with dependable crop production. Yet savvy growers know that reliable plant growth and optimal yield depend on a balanced combination of nutrients, some of which are made available to plants quickly—and others that are made available over time.

The slow-release benefits of crushed volcanic basalt make it an effective way to minimize deficiencies, particularly with fast-growing crop plants that experience periods of rapid nutrient uptake.

What is basalt and why is it good for my garden?

On May 18, 1980, Washington’s Mount St. Helens awoke from 120 years of dormancy and erupted, sending volcanic ash into the atmosphere and depositing it in 11 states. It was difficult to imagine at the time that any signs of life could emerge from the surrounding landscape, which was covered with dark gray ash and resembled the moon.

Yet nature’s regenerative abilities quickly took over. In some cases, agricultural farmlands that were downwind of the eruption saw long-term, beneficial effects as a result of the mineral-rich volcanic basalt that was deposited on the soil in the form of ash. Some of the richest, most fertile soil on the planet is found near active volcanoes. This explains why people throughout civilization have been willing to settle near volcanoes despite the potential dangers.

By releasing essential minerals and nutrients, rock deposits are essential to healthy plant growth and increased agricultural yields. However, not all rock amendment products are alike. For balancing overall soil health, basalt stands out from other rock materials. Created through the cooling and solidification of magma and lava, basalt is the rock material that makes up most of the soils around the world.

Compared to other volcanic rocks that are high in quartz, basalt weathers relatively quickly. It begins to release nutrients to plants as soon as the roots make contact. Additional nutrients become available with ongoing decomposition, thereby resulting in a steady flow of nutrients over time.

Using volcanic basalt powder (often referred to as rock dust) as a soil amendment is not new. In the 1930s, researchers in Europe used finely ground basalt to treat and improve the productivity of degraded forest lands. One of the most comprehensive studies on the benefits of crushed basalt came from D. Hotman de Villiers, who conducted a series of long-term field trials on highly degraded soil that led to increased sugarcane yields on the island of Mauritius.

The tests started as early as 1937 and resumed in the 1940s and 1950s at the Sugar Cane Research Station of Mauritius. Scientists commenting on de Villiers’s work note several reasons behind basalt’s effectiveness as a soil amendment, including improved silicon nutrition, enhanced trace element supply, alteration of the soil’s physical properties and modification of mycorrhizal populations.

Further studies have shown that a major mechanism influencing positive crop response on highly weathered soil is basalt powder’s ability to increase soil function and productivity as measured by cation exchange capacity.

Today, scientists across the globe continue to research the benefits of basalt. While plant species vary widely in their nutritional requirements, volcanic basalt is proven to improve root systems, increase yields and promote general plant health in a wide variety of crops and conditions—including those in indoor growing situations, where mineral deficiency can be an issue.

The Building Blocks of Soil

Chemically synthesized fertilizers are designed to feed plants fast. They cover the necessary macronutrient requirements and contribute to rapid leaf growth. In that sense, they do their job well. Yet there are a multitude of secondary nutrients, micronutrients and trace elements that aren’t available in most commercial fertilizers that plants require to reach their maximum potential.

For evidence, we need only to observe the self-preserving behavior of plants themselves. Indeed, plants aren’t nearly as passive as most of us might imagine. Given the opportunity, plants will actively seek to acquire nutrients from their surroundings to overcome any imbalances. Recent research shows that fine roots will attack rock particles as a physiological consequence of mineral deficiency.

In soil that is properly mineralized, plants don’t have to work nearly as hard to survive. Rich in micronutrients like calcium, iron, magnesium and manganese, volcanic basalt helps increase root growth and boost crop yields.

Basalt also contains soluble silicon that contributes to the strength of cell walls and makes crops more resistant to pests and disease. It also strengthens stems, helping plants stand tall and capture more light to maximize photosynthesis.

Not surprisingly, vibrant, healthy plants grown in remineralized soil have greater Brix levels than plants that are nutrient deficient. As a measure of dissolved plant sugar and nutrients, higher Brix levels indicate balanced and healthy growing conditions. Healthier plants also produce more fragrant flowers with greater concentrations of essential oils and better-tasting, more nutritious fruits and vegetables.

Should I be adding basalt to my indoor plants?

The stable plant materials that make up potting mixes, such as bark, peat and coir, are like soil in some ways—and unlike it in others. Like soil, potting mixes physically support plant growth.

Potting mixes are porous enough to hold a mixture of air and water and they offer lots of surface area to act as an interface for root surface exchange. Soil, on the other hand, is derived from a marvelously complex interaction between biology (soil micro-organisms and plant material) and geology (decomposing rock material).

As the geology reacts with the biology, the rock releases elements like calcium, magnesium and iron in different proportions than the plant material in potting mixes. Adding crushed basalt to potting mixes more closely mimics the geological and biological interactions in healthy soils.

In hydroponic systems, incorporating rock material can take on various forms and use different textures or particle sizes. Coarse basalt particles with fine particles removed can be used as a rooting media.

Medium and fine basalt particles can be added to existing rooting media or to compost tea. Fine basalt particles that partially suspend in water can be added to hydroponic solutions where roots can latch onto particles. Be sure to exercise caution for pumps and other equipment with this last approach.

By mimicking the slow process of the Earth’s method for producing healthy soil, crushed volcanic basalt helps support the biological processes required for optimal and sustainable plant growth.

Well-suited to the needs of most indoor growers, volcanic basalt produces relatively little ambient dust and is easy to add to most indoor growing mixes. Moreover, a little goes a long way.

A small quantity of high-quality volcanic basalt is all it takes to provide plants with the essential minerals they need to stay strong, healthy and resistant to disease. For best results, look for products that are listed by the Organic Materials Review Institute for use in organic production.