What is the optimal light intensity for the vegetative stage?

Every grower wants their plant to max out the flower production of their plants, both in terms of quality and quantity. At the same time, before the plant gets into the flowering stage, it has to go through the vegetative stage. The importance of this part shouldn't be underestimated because, during this time, the plant would develop those morphological characteristics that would make it strong and healthy enough to withstand, indeed, flower production.

One of the main ways to drive the plants' growth is through the use of specific lighting strategies, especially when it comes to providing them with optimal light intensity. The issue, however, is that each of the growth stages has different light intensity requirements; on top of that, the best post-vegetative plant morphology depends on the production system in use. In any case, the main goal of the vegetative stage is to ensure that the plant would get into the flowering with a specific height, thickness, branching, leaf size, and so on. Thus, it goes without saying that the light intensity during the vegetative stage should promote the development of the aforementioned attributes.

Melissa Moher and team conducted a study to further understand the optimal light intensity to provide plants within an indoor setting to ensure healthy and robust growth during the vegetative phase. More specifically, the aim was to ‘determine the effects of a broad range of light intensity on vegetative stage cannabis morphology and growth attributes, to guide cultivators towards optimizing the light intensity for their specific production strategies.’

The researchers’ goal was to grow a plant designed to ‘optimize future photosynthetic capacity, facilitate airflow within the crop canopy, maximize potential flowering sites, and bear the weight of mature inflorescences.” Of course, the authors don’t aim at making any one-fits-all, generalizing statements, as each cultivar has its own specificities which a grower has to address. Yet, knowing a ground to start from gives growers that additional scientific info that might do the magic in their cultivation scenario.

Thus, to understand the plant response to light intensity during the vegetative phase, the authors grew ‘Gelato’ plants for 21 days with canopy-level PPFD ranging between 135 and 1430 µmol·m-2 ·s-1 31 on a 16-hour photoperiod. The experiment to place in a cannabis greenhouse facility based in Southern Ontario, Canada.

The plants were then harvested 21 days into the light intensity treatment. The results showed that PPFD levels between 600 and 900 0 µmol·m-2 ·s-1 gave a very good balance with regards to the optimization of crucial morphological parameters while minimizing the energy use caused by excessively high light intensities. As said, such a finding is far from applying to all the indoor settings and all the cannabis genetics. As the authors put it: “Although the desired […] attributes […] will be subjective to each genotype and production scenario, the presented light intensity responses can assist cultivators in optimizing the light intensity for their individual production goals.”

Source: preprints.org


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