Most gardeners are aware of the benefits of using either Perlite or Vermiculite as an additive soil ingredient, but few understand that Biochar is the perfect alternative!
Many common potting soil ingredients, such as Perlite, Vermiculite, Peat Moss, Bark, Wood Chips, and Charcoal, serve similar functions in the garden. These materials are generally moisture-retentive and inert, helping to prevent soil compaction, retain moisture, and improve aeration and drainage. They are also widely used for propagating new plants, cultivating seeds, and supporting indoor container gardens, composting, and lawns.
Switching to Biochar offers both financial and ecological advantages over Vermiculite and Perlite. As these materials become increasingly expensive, particularly for commercial nurseries, locally produced Biochar can be a more cost-effective alternative. It also has a significantly lower environmental impact, with less harmful production and transportation processes.
Vermiculite and Perlite have a high carbon footprint due to their energy-intensive production, which involves heating them to extreme temperatures (100–500°C higher than the temperature used to make high-quality Biochar). Additionally, these materials are often imported from distant locations, further contributing to their environmental cost.
In contrast, our locally produced Biochar is made from wood that would otherwise be burned, chipped, or left to decay, all of which release CO2 back into the atmosphere. Biochar's carbon sequestration, when buried in the soil, is nearly permanent, effectively locking CO2 away for hundreds of years while simultaneously improving soil health and fertility.
Water Retention
Biochar can absorb up to six times its weight in water, making it an excellent option for moisture retention in the soil.
In comparison, Vermiculite and Perlite can each absorb 3 to 4 times their volume in water.
Both Perlite and Biochar retain water due to their large surface areas, which are covered with tiny pores and crevices. However, Biochar and Perlite are more porous than Vermiculite, which allows water to drain more freely and helps improve soil aeration. This makes them particularly useful for plants that benefit from higher humidity levels, as the water evaporates from their larger surface areas, creating a more humid environment.
While Biochar, Perlite, and Vermiculite are all effective at retaining water, Vermiculite acts more like a sponge, with strong capillary action that enables it to hold significantly more water. However, this higher water retention comes at the expense of aeration, which can limit oxygen availability for plant roots. This makes Vermiculite a better choice for moisture-loving plants that require consistently damp conditions.
Soil pH
Soil pH is a measure of how acidic or alkaline the soil is. A pH of 7.0 is neutral, while a pH below 7.0 is acidic and a pH above 7.0 is alkaline. This is important because it affects what plants can grow in it. For example, an acid-loving plant will suffer and die if it's planted in alkaline soil, and vice versa.
The average soil pH in the UK is neutral, or slightly lower at around 7, however it can vary from 4.0 to 8.5.
Our Biochar: has a pH level of around 7.5–8
(Some other forms of Biochar tend be more alkaline to varying degrees).
Perlite: is neutral with a pH of 7.0–7.5, but it has no buffering capacity and contains no mineral nutrient.
Vermiculite: has a pH of 7.0–7.5.
Mineral Adsorption
Why Biochar is the Superior Choice: When it comes to mineral adsorption (The ability of a material to absorb and retain essential plant nutrients) Biochar stands out as the most effective and sustainable option compared to Vermiculite and Perlite.
Biochar is a powerful tool for improving soil fertility. Its highly porous structure, created through pyrolysis, provides an extensive surface area that can adsorb a wide range of essential nutrients, including calcium, magnesium, potassium, and micronutrients. This not only helps to prevent nutrient leaching but also makes nutrients available to plants in a slow-release manner, triggered by microbial activity.
Unlike Vermiculite and Perlite, Biochar’s capacity to host beneficial soil microbes further enhances nutrient cycling, ensuring that your plants have a steady supply of minerals for long-term growth. Additionally, Biochar holds over 50 trace elements crucial to plant health, making it a truly comprehensive soil amendment. By adding Biochar to your garden, you’re not just improving mineral retention - you’re creating a thriving environment for both plants and soil microbes.
In contrast, Vermiculite does retain water and some nutrients, but its nutrient retention is limited compared to Biochar. While Vermiculite holds nutrients like calcium and magnesium through its high cation exchange capacity (CEC), it lacks the long-term stability and microbial support that Biochar offers. Over time, Vermiculite’s nutrients can leach out, especially with heavy watering or in poorly managed soils. It’s also important to note that Vermiculite doesn’t contribute as much to the overall fertility of the soil - its benefits are more focused on moisture retention.
Perlite, while excellent for improving drainage and soil aeration, has very little capacity to adsorb or retain nutrients. It’s an inert material, meaning it doesn’t contribute to the soil’s mineral content or support microbial life.
Biochar
Biochar can be thought of as a habitat not a fertiliser, because it serves as a carrier for plant nutrients, making them available as and when the plants need them via microbial symbiosis.
Biochar needs to have the right pores accessible and habitable to microbes. Too small or powdered and these pores don't exist, too large and they are inaccessible. We recommend between 0.1 and 5mm.
The thermal process which produces biochar is called pyrolysis which involves burning at very low oxygen levels. Our Biochar is made from British Hardwood which is pyrolysised at around 750°C. (Lower quality Biochar can be made from many plant products and at different temperatures 300–1000°C).
During this process many trace elements (over 50 metals) crucial to plants are adsorbed to the carbon structure, preventing them from leached out, yet keeping them accessible to microbes and plant roots.
Fresh biochar may adsorb nutrients from the soil, causing a temporary negative effect on plant growth. This can be avoided by Enriching the Biochar before use, allowing it to soak up vital minerals and nutrients (as well as microbes) which are all later released to the plants.
An added benefit is that by adding 10–30% biochar (by volume) to your compost to enrich it, can help speed up the composting process by around 30%. The resulting compost is also a highly efficient substitute for peat in potting soil!
Biochar helps to absorb excess fertiliser, preventing run-off into water systems, while retaining the nutrients in the soil for the plants to access. If nitrogen fertilisers are applied in the wrong amounts or quantities some bacteria act on it making Nitrous Oxide which is over 200 times more effective at trapping heat in the atmosphere than Co2.
Vermiculite
Vermiculite is derived from hydrated Magnesium Aluminium Iron Silicates, which are extracted from rocks containing minerals like Biotite and Iron-bearing Phlogopite. These minerals are then heated to temperatures between 800–1100°C, causing them to expand significantly.
Vermiculite is highly valued for its low density, thermal conductivity, and excellent water retention properties. It is most commonly available in particle sizes ranging from 0.1–2 mm, 2–4 mm, and 4–8 mm.
Commercial Vermiculite mining operations are widespread, with large mines located in countries such as the USA, Russia, South Africa, China, and Brazil. The Vermiculite is sourced from rocks rich in large mineral crystals, which, when exposed to the elements, break down and react with water and other chemicals.
The manufacturing process involves two key steps: First, Vermiculite containing rocks are extracted from large open pit mines, then crushed and transported for further processing. In some cases, these rocks may contain trace amounts of asbestos, which can pose health risks. The extracted material is then processed using methods like froth flotation, gravity separation, or electrostatic separation. The final step involves heating the material to expand it into granules, a process that often takes place at a separate facility, sometimes far from the mining site.
As of 1999, global reserves of Vermiculite were estimated at around 55 million tons. In 2016, worldwide Vermiculite production reached about 404,000 tons, with production levels continuing to rise.
Perlite
Perlite is a glassy volcanic rock formed when lava rapidly cools as it erupts from a volcano. It has a high silica content and contains about 2–5% water, which is trapped during the cooling process. When heated to temperatures between 870–1100°C, the water inside the Perlite turns into steam, causing the material to expand by 4 to 20 times its original volume. This expansion creates a highly porous and lightweight substance.
Perlite typically comes in sizes ranging from 0.1–2 mm to 1.5–3 mm in diameter. The different grades of Perlite vary in their physical properties and are used for various applications, including in potting soil mixtures, as a standalone growth medium, and as a soil enhancer.
Approximately 70% of the world’s Perlite is produced along the Aegean coast in Turkey, where it has an annual production of about 5 million metric tons. Other major producers include the USA, China, Greece, and Italy. The global reserve of Perlite is estimated at around 700 million tons.
Pros and Cons of Biochar, Vermiculite, and Perlite
Biochar Pros:
Sustainable and Local Production: Typically made from waste biomass, reducing carbon emissions.
Long-Term Carbon Sequestration: Biochar locks carbon in the soil for hundreds of years, helping mitigate climate change.
Improved Soil Structure: Enhances soil aeration, water retention, and microbial activity.
Nutrient-Rich (When enriched): Adsorbs and slowly releases nutrients to plants over time, boosting soil fertility.
Microbial Habitat: Provides habitat for bacteria and mycorrhizal fungi.
Environmental Benefits: Reduces the need for peat and prevents excess fertilisers from leaching into water systems.
Biochar Cons:
Initial Nutrient Imbalance: Fresh Biochar may initially deplete soil nutrients, as it has a strong adsorption capacity that can temporarily "lock up" essential minerals. (However, this effect can be easily mitigated by enriching the Biochar before use, allowing it to absorb vital nutrients and microbes, which are then gradually released to plants. For more details on how to properly prepare Biochar for use in your garden, read our article: How to Enrichment Biochar).
Vermiculite: Pros
High Water Retention: Great for moisture-loving plants.
Vermiculite:Cons
Environmental Impact: Involves destructive mining and long-distance transportation, increasing its carbon footprint.
Nutrient Deficient: Does not hold or release nutrients like Biochar.
Cost: Continues to rise as demand grows and reserves dwindle.
Perlite Pros:
Improves Drainage and Aeration: Especially helpful for plants that need well-drained soil.
Perlite Cons:
Energy-Intensive Production: Requires high temperatures to create, contributing to energy consumption.
Non-Nutrient Retentive: Does not hold or release nutrients.
Environmental Impact: Mining and transport have a significant environmental cost.
Our Conclusion
Biochar stands out as a superior and more sustainable alternative to both Perlite and Vermiculite for nearly all the same applications in gardening and soil management. It provides the same benefits of water retention, soil aeration, and improved drainage, making it just as effective in potting mixes, seed propagation, and container gardening. In fact, Biochar’s ability to absorb up to six times its weight in water - far exceeding Vermiculite and Perlite, while maintaining superior aeration and supporting microbial activity, makes it a more versatile and long-lasting choice.
Beyond its practical uses, Biochar offers unparalleled environmental benefits. Unlike Perlite and Vermiculite, which have significant carbon footprints due to energy-intensive production processes and long-distance shipping, Biochar is made locally from waste materials, often from sustainably managed forests. It also sequesters carbon in the soil for hundreds of years, playing a crucial role in mitigating climate change.
While Vermiculite and Perlite may have been the go-to options for moisture retention and aeration, Biochar is the more sustainable, cost-effective, and ecologically responsible choice. It not only meets the same functional needs in the garden but also brings added long-term benefits for soil health, microbial life, and the environment.
By making the switch to Biochar, gardeners can not only improve the vitality of their plants and soil but also make a positive impact on the planet. Choosing a sustainable solution today means healthier gardens tomorrow, while reducing your ecological footprint and helping combat climate change.
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