An Introduction to Living Soil in Cannabis Cultivation
By Lauren Kurtz, Ph.D.
We are incredibly grateful to our guest blogger, the esteemed Lauren Kurtz, Ph.D., for this foundational introduction to what exactly living soil means. Lauren is a widely published scientific writer who recently completed her Ph. D. at UConn in Horticulture and Plant Breeding. She has plans to pursue a career in sustainable horticulture. Follow Lauren and connect with her on Linkedin.
❤️The High End
As the demand for high-quality cannabis becomes a necessity in competitive markets, indoor growers are increasingly turning to living soil systems to enhance the quality of their flower and minimize their environmental footprint, but what exactly is ‘living soil’ and how is it different from regular soil?
Let’s start with plant nutrition. Plants absorb nutrients from the soil surrounding their roots. There are 17 elements that are essential to plant growth. Plants require a delicate balance of macronutrients including nitrogen, phosphorus and potassium; and micronutrients like iron and zinc. These elements are provided to the plant from natural processes taking place in the soil or through added fertilizers. The soil acts as a pantry, storing and delivering these nutrients to plants in a form they can absorb. Outdoor natural mineral soil is a combination of sand, silt, clay, organic matter, bacteria, fungi, and arthropods. The exact recipe depends on the location and the management practices of a particular soil. Mineral soil is more than just a growing medium, it’s a complex, interconnected system that includes the soils physical, chemical, and biological properties. All of which influence nutrient availability for your plants.
On the other hand, most cannabis is grown indoors in containers filled with potting media or soilless substrates like rockwool. Most of the commercially available potting media is a sterile mix made from a base substrate of peat or coir with the addition of perlite, vermiculite, bark, and/or fertilizers. Most crops grown in potting media are provided readily available nutrients directly through irrigation water in the form of synthetic fertilizer salts. This system is different from growing in mineral soils where the plant roots are part of a larger nutrient cycling system. It’s important to recognize these differences before understanding what ‘living soil’ is. Growing in ‘living soil’ combines the best parts of natural mineral soil and potting media to achieve a more holistic approach to production.
Living soil is a growing trend in cannabis cultivation to improve the sustainability of the operation and enhance the quality of the flower. Living soil uses a “souped-up” potting media that imitates natural nutrient cycling in mineral soils through the use of microorganisms and organic amendments to provide nutrients to the plants. The base of living soil mixes are high in organic matter and use more sustainable materials like coir or composted bark as a base media. Using living soil is a less resource intensive approach to growing, mainly due to the fact that soil mixes are amended regularly and reused for several crop cycles. Traditional potting media is not reused, which is problematic when the base material is peat that is not sustainably harvested.
Many crops grown in potting media are fertilized with water soluble synthetic fertilizers, which are mined or are made from petroleum byproducts. These salt-based fertilizers exclude beneficial microbial life in the root zone. The plants essentially grow without the symbiotic relationships with bacteria and fungi that they would normally have in healthy mineral soils. The fertilizers used in living soil aren’t salt based, they are derived from organic materials such as worm castings, alfalfa, kelp, oyster shell and fish bone meal. These materials are broken down into usable plant food by the microorganisms present in living soil mixes.
Microorganisms in living soil are added to the mix by commercially available inoculants or by using soil amendments that are rich in bacteria and fungi. Compost teas and ferments are another way to introduce microorganisms in the living soil mix. The presence of beneficial bacteria, fungi, nematodes, and arthropods present in living soil add ecological diversity to the cultivation environment. Living soil creates a more diverse ecosystem than in regular potting media and emulates the diversity of life present in mineral soil systems.
