This is how spectral tuning will improve cannabis propagation and plant morphology

In practice, rooting cuttings and growing young cannabis plants is often a process that is far from uniform. Better performance in this crucial cultivation stage has a major impact on the final results. The root development can be controlled better by means of a dynamic light recipe, resulting in a shorter cultivation time, more homogeneous growth and better-quality flowers at the end. Due to the shortened cultivation time, the number of cultivation cycles can reach up to six per year. An additional advantage is that the use of rooting hormone powder, which is not permitted in some countries, becomes unnecessary. In addition, rooting hormone chemicals can sometimes hamper the proper root development.

Signify has developed dynamic Philips LED light recipes (spectral tuning) for better results in the rooting and growing phases of cannabis plants. Specific control of root and shoot development results in faster, more uniform plant development in the vegetative and flowering stages. The faster shoot development and better shoot quality lead to higher yields with a shorter cultivation time. The key to success is a light recipe with a specific ratio of red and far-re­­­d light during the root induction phase, in combination with the right light intensity. Dynamic grow light is also a powerful control tool to influence plant structure (morphology) during the vegetative growth phase.

Root development

The basis for successful cannabis cultivation is laid while growing the cuttings to young plants. Cuttings must form roots, and they do so under the influence of the plant hormone auxin. Auxin is formed in the apical shoot of the cuttings on the mother plant. From there, auxin is naturally transported to the base of the cutting where it is needed to induce rooting. This process is partly influenced by the prevailing light conditions. The phenomenon is known as shade avoidance response. The spectrum (the ratio of red to far-red light) and the light intensity are both important here. In the right proportions, light can induce a rapid production of auxin and its transportation to the root zone. When the light intensity is too high, the auxin is rapidly broken down, which weakens the stimulus to form roots. The application of a dynamic light recipe makes the use of rooting hormone, which is permitted in some countries and not in others, unnecessary. This is good, because it reduces the risk that any contamination of mother plants is transmitted via the rooting hormone powder to cuttings that come from healthy plants. In addition, the rooting phase is shortened by several days.

Influencing plant morphology

After the rooting phase, the uniform batch of plants should grow quickly (vegetative phase) before flowering (generative phase). Dynamic growth light also appears to be useful in the pre-vegetative transition phase from rooting to vegetative growth. At this stage, the spectrum can be used to influence further morphological development of the plant and the quality of the shoots. Control of the number of branches and control of internode length can be achieved with spectral tuning. Mostly, this is achieved by playing with the red/blue ratios and the red/far red ratios.

When growing in multi layer systems, the available height is usually limited. In that case, tuning it towards a compact plant with shorter internodes may be desirable. Depending on the characteristics of the variety, it is also possible to control stretching (longer internodes).


Dynamic grow light in practice

Optimization of spectrum and light intensity in this crucial development phase results in faster, healthy root development, more vital young plants and more uniform, vigorous growth. With a dynamic Philips GreenPower LED installation in combination with the Philips GrowWise Control System, cannabis growers can perfectly match both the spectrum and the light intensity to the different cultivation phases for their various species. They can also be the first to benefit from the knowledge and experience developed for the Philips LEDs, which is enriched daily based on laboratory and practical research. Lastly, several customers are starting to use spectral tuning on early growth phase. More to be shared later. Stay tuned.

Dr. Celine C.S.

Dr. Céline C.S. Nicole-de Groot is a researcher at Philips since 2001 and program leader for the indoor farming research in the Netherlands. She has expertise in physics, chemistry, thermodynamics, plant sciences, light and sensing technology. The last 14 years, she has accumulated expertise in technology, light for greenhouse and indoor horticulture. Specialized on Cannabis research since 2018 where she coordinates open innovation and University research on indoor cultivation.

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