Here in the UK we recommend the use of Carbon Gold Multipurpose Compost with Biochar, as a choice of potting media.
This mix is peat -free and is proving ideal working in combination with the active vertical wormery core.
The coir base of the compost is high in lignin which provides excellent structure in a vertical system and won’t degrade too quickly. This is important to prevent compaction and also settling out of finer particles, which would accumulate at the lower level and reduce free-drainage. Coir also provides a great environment for worms, and will last a number of years in a regenerative system like the Garden Tower. The biochar inclusion however is where some real magic happens as biochar has some amazing properties:
- The micro-porous structure provides a excellent habitat for the proliferation of beneficial soil biota.
- The micro-porous structure of biochar benefits water retention in the soil.
- The surface area of biochar has been demonstrated to be anywhere from 10 to 300 m2 /g (activated charcoal has a surface area of up to 2,000 m2 /g!), most of which is found internally and provides ample area for microbial habitat.
- The large surface area of biochar can attract and hold all mineral ions – not only cations (+) such as ammonium, calcium, magnesium and potassium, but also anions (-) such as nitrogen, phosphorus, sulfur, and boron. By attracting and holding both positive and negative nutrient ions in the soil, biochar can reduce both leaching (into groundwater) and out-gassing (into the atmosphere). These loosely-held nutrients are bio-available to microbes and plant roots in the complex root zone.
- Biochar can improve soil texture and workability, particularly heavy clay soils, although it has shown great promise in all soil types.
- Recent studies have shown that plants grown in biochar as a growth medium (at concentrations as low as 1 to 5% of the total soil mixture) tend to have a higher resistance to pests and diseases (i.e., systemic resistance) (Elad et al., 2010).
- Biochar’s natural affinity for nitrogen allows it to arrest the flow of the nitrogen cycle. It tends to only release as much nitrogen into the surrounding soil as is needed by microbes and plants to maintain healthy growth (ScienceDaily, 2010)
adapted from (Biochar – An Organic House for Soil Microbes by Bryan Hugill 2011)