Coir-based growing substrates for indoor cannabis production

Cannabis production for both medical and recreational purposes is an expanding industry in North America. Due to the historically illegal nature of this crop, scientific literature on cultivation is lacking, specifically with regards to growing substrate use and management. To evaluate coir-based growing substrates for the vegetative and flowering growth stages of cannabis production, two trials were conducted in walk-in growth chambers. In the first trial, plants were grown in three substrates: two coir-based organic substrates, i) ABcann UNIMIX 1 (U1); ii) ABcann UNIMIX 1 - HP (U1-HP) and a commercially available peat-based organic substrate; iii) PRO-MIX MP ORGANIK MYCORRHIZAE (PM-V). The coir-based substrates differed primarily in container capacity, U1 having higher container capacity (CC) than U1-HP. In the second trial, two other coir-based substrates were evaluated: i) ABcann UNIMIX 2 (U2); and ii) ABcann UNIMIX 2 - HP (U2-HP), with U2 having higher CC than U2-HP. Plants in both trials were container-grown and fertigated using liquid organic fertilizer at ≈30% substrate moisture content. In trial 1, after the 22-day vegetative growth period, all plants were transplanted into the same substrate and maintained under a 12-h photoperiod to initiate flowering and allow the measurement of dry floral weight (yield). Treatments in both trials were evaluated on their effects on plant health, growth rates and dry floral weight. It was concluded that either coir-based substrate (U1-HP or U1) is effective for cannabis production during the vegetative stage, and in the flowering stage, the drier coir-based substrates (U2-HP) may be preferred as it delivered 29% higher yield.