Adding charcoal or “biochar” to soil can boost soil’s water holding capacity and reduce the need for fertilizers, which is well-known in the agricultural industry but as of yet has not caught on in the horticultural realm and growth media industry. Research, led by growth media company Fafard & Frères, in Quebec, suggests that biochar may be a good replacement for perlite and possibly, peat moss.
Growth media are considered to be solid materials, other than soil, which can support plant life on their own or in combination and possibly create superior growing conditions in comparison to regular agricultural soils. Perlite, vermiculite and peat moss are growth media most commonly used by the horticultural industry. Recently, the industry has begun searching for alternatives due to rising costs and lower product availability. Also, as these industries move towards more sustainable practices, costly, energy intensive and environmentally unfriendly methods such as mining peatlands and producing vermiculite and perlite become less desirable.
Substitutes for growth media are difficult to come by, good products must be weed and toxin free, homogeneous, physically and chemically balanced and able to support and provide for the needs of growing plants. Additionally, the demand for products whose development and use is of low impact to the environment is growing. Biochar is produced by aerobically burning organic material which makes it resistant to microbial decomposition meaning that it can store carbon for a long time. Researchers at Fafard & Frères investigate biochar produced from 3 different sources: 1) sugar maple and yellow birch logs, 2) balsam fir, white spruce, and black spruce and 3) from hardwood waste byproducts. These species were chosen primarily because they were locally available, reducing the need for long-distance travel which in turn lowers cost and environmental impacts. Additionally these differing stocks provided varying particle size distribution which imparts a range of properties to growth media produced there from.
The research team then created 5 different growth media in order to compare how biochar performed in comparison to typical substrates; the first was composed entirely of peat moss, the second was 70% peat moss and 30% perlite, and the remaining three replace perlite with one of the biochar types. When put through a sequence of tests the media consisting of partly biochar performed as well or better than traditional media. The biochar appeared to improve nutrient retention and increase pH, which can aid in neutralization of acid soils but in excess of 30% of substrate it may push pH beyond acceptable levels for growth.
There are, of course, other issues with using charcoal as a soil amendment. Handling biochar produces black dust, which can be controlled but at a cost. It is also not a standardized product; properties will vary vastly among feedstock species and production method. More research needs to be done to establish how it will affect plants in the long-term and how to produce it to meet high industry standards. Although biochar is not perfect, it is important to support ongoing research and stay informed about new products which could improve the industry, reduce energy usage and decrease environmental impacts.