Maximizing yields per square meter of grow space and producing a consistent quality medicine are top priorities in the pharmaceutical cannabis industry. Both Greenhouse and indoor cultivators have experimented with many techniques over the years, with two methods standing out: the so-called “Sea of Green” and the “Screen of Green”.
Sea of Green (SOG)
Sea of Green was developed in the early days of medical cannabis in California: the first US state, and first place in the world which allowed the use of cannabis as medicine. Large scale growers, supplying medical cannabis dispensaries, wanted to provide large quantities of consistent quality cannabis for patients. This led to the widespread use of clones for cultivation. Clones are branches which are cut from a mother plant, and induced into rooting through the use of natural acids and hormones, and a specialized humid climate. More details on the production of clones will be discussed in our next month’s issue.
Clones are genetically identical to their mother plant, and one can cut hundreds of clones from one mother. The variations in flowers produced from these plants are therefore limited only to the differences they experience in the external climatic conditions of the grow space. By keeping the cultivation environment as uniform as possible in all areas, one can greatly reduce any variations in size, structure, THC and cannabinoid content. With SOG, rooted clones are placed in a small container with the desired substrate, or planted in 10cm x 10cm rockwool grow cubes, and given only 3-5 days to acclimate, before the photoperiod is changed to a 12-hour light/ 12-hour dark cycle to induce flowering.
Because they are switched to the flowering cycle when they are small, considerable numbers of clones must be used to fill a cultivation space using the SOG method. The plants do not have time to form many side-branches, and therefore, each one consists mainly of one top, with just a few small side flowers. Average dry flower yields per plant can be between 8 -15 grams, if other growing conditions are optimal. However, because of the large number of plants involved (50-80 plants in 10 cm x 10 cm pots or grow cubes in a 1 square meter area), yields per square meter can reach 0,8 – 1 kg, which is a highly efficient yield.
Clearly, SOG is most practical when the mass production of healthy clones has been established. This method can shorten the time it takes for an operation to reach its maximum production level, eliminating the vegetation period needed to achieve bigger yields per plant. However, cultivators must be vigilant with climate control and pest prevention using this method; the large number of plants can lead to increased humidity levels, and create an environment which attracts insects and molds.
Screen of Green (ScrOG)
When making or obtaining a steady supply of clones is not possible, growers compensate by vegetating their plants for a longer period of time, increasing yield per plant. Clones or plants from seed are usually placed in pots which are bigger than those used in SOG, and allowed to vegetate for a period of anywhere from 10-21 days before they are triggered into flowering. This means the plants are usually taller, and have many more side branches compared to the flowering clones in SOG. If these branches are crowded together, causing them to shade each other out, yields are lowered, and space is not used efficiently. Therefore, “screens” of horticultural trellis netting are used to train the branches apart and ensure that light is reaching as many bud sites as possible on each plant.
Netting can be installed in various styles, curved, horizontally or vertically. Two layers of netting can also be used. As the plants grow, their branches are gently bent apart through the screen. With this method, it is completely up to the cultivator how many plants will fill a square meter space. The fewer plants used, the longer they must be vegetated to achieve enough bio-mass to fill the area. The netting allows precision placement of branches, and therefore one can maximize the space with flower production sites, leaving no appreciable gaps. Although vegetating time is longer with ScrOG as compared to SOG, yields per square meter are higher with ScrOG, because more space is being utilized by the plants. Skilled growers have been able to achieve yields of up to 1,5 kilos per square meter using this method. ScrOG is more labor intensive than SOG, due to the time spent training the branches through the screen, and increased pruning simply because one is dealing with larger plants. However, less pots/grow cubes in the space mean less humidity is created from evaporation of irrigation water, making pest and mold control easier.
Overall, these techniques both have their own advantages and drawbacks; based upon this information, it is up to each cultivation company to determine which method fits their personal production goals, capacity, and space.
By Angela Swift