Which of these most resembles an indica?

Growing with LED

Mr. José / info@pestovat.cz

Growing cannabis under artificial light has long been more than just sodium-vapor and metal-halide lamps. Over the last decade, LED technology has earned its rightful place above plants, and the future of this technology is more than promising. Growing with LED modules has its specifics, pros and cons. In the following article, you will get to know the most important features and also learn about the results of one particularly interesting research.

HOW IT ALL BEGAN

When LED modules started appearing on the plant-growing market several years ago, I was curious how long it would take for them to reach the quality of traditional, high-intensity lamps. My first experience with LED was not too bad, on the contrary. The plants grew strong with dark green color and their flowers were strong and stiff, too. That includes the lower ones, which does not always happen even under sodium-vapor lamps. You could see at first sight that the flowers were completely covered in resin. The taste, smell and effects of the first LED-

grown harvest were all excellent, as several people that were able to try it have confirmed. The crop was not the richest, but considering the lower power consumption, it was still above average. On the other hand, if I used a sodium-vapor lamp over the same growing area, I would get at least 50% more in the same amount of time. One of the reasons for that is the fact that I used a 300 W LED module instead of the original 600 W sodiumvapor lamp. With the knowledge from my first experience, I would have now rather used LED module rated for more than 400 W. The plants growing under the LED light were shorter than I was used to, they had thicker stems and were generally more compact. The second harvest had the same qualities as the first one, but its quantity has decreased. The reason for that was a decrease in room temperature compared to the first growth cycle. This temperature difference was caused by coming winter. From my experience with sodium-vapor lamps, I was used to dealing with temperatures that were too high instead of too low, and that is why the area was not artificially heated.

As you can see, I have encountered several differences in cultivating under LED lights compared to sodium-vapor lamps from the very beginning. During that time, the reactions of people trying from the ground up, it is important to account for a heating unit for the cultivation area, especially during winter or in colder regions. The optimal temperature for proper plant growth is 24-28 °C. For growing plants under LED, it is better to keep it between 26 and 29 °C. It is also important to keep the humidity higher, ideally around 60 %. Even under LED lights, there is still the risk of mold in the last weeks of flowering, of course. That is why the humidity should be decreased to 40 % in the last two to four weeks before harvest. While the climate conditions change rapidly thanks to the variable running times of sodium-vapor lamps, LED

lights do not affect them too much. That is a big advantage, especially for domestic growers in warmer regions, where the temperature does not drop below 20 °C and usually stays above 30 °C in summer.

Right away, we can tell that LED light has a different light spectrum… …compared to the spectrum of sodium-vapor lamp.

LED were mostly negative. The modules were expensive, and the outcomes did not reach the promised results or savings. Many resellers promised unrealistic decrease in power consumption but were unable to provide the necessary information for growing under LED lights. The situation has completely changed since then and even people that were totally against LED modules in the beginning are trying them now.

CLIMATE CONDITIONS FOR LED CULTIVATION METHOD

The intensity of the lighting and the composition of the light spectrum emitted by the light source significantly affect the morphology of plants, the formation of their resin, the amount of cannabinoids and other active substances. The light from sodium-vapor lamps is rich in green, yellow and red spectrums. The plants grow taller and have larger internodal gaps under this type of light. Most sodium-vapor lamps are weaker in the blue spectrum. The versions with added blue spectrum have a lower amount of red spectrum light. In comparison, most LED modules for cultivation are stronger in the blue spectrum but not as strong in red and yellow spectrums. This results in a shorter plant height and smaller internodal gaps. High-end LED modules allow the user to adjust the emitted spectrum according to their needs, which can differ depending on the vegetative phase the plants are currently in.

Another important factor is the fact that sodium-vapor lamps cannot be hung too low above the plants without cooled reflectors thanks to their high operational temperature. LED sources can be hung right above the plants. Thanks to the power savings of LED modules, we usually replace stronger sodium-vapor lamps with less powerful LED modules, but these have a lower light intensity when comes to increasing distance between plants and them. Because of this lower intensity, the light does not penetrate in such amounts deeper into the growth. That is why it is better to grow shorter plants to reach optimal results, so that the distance between the top and bottom flowers is as short as possible. The aforementioned higher amount of blue spectrum helps that already, but it can also be achieved using SOG or ScrOG methods.

IRRIGATION AND FERTILIZATION

When the temperature in the cultivation area is lower and the plants grow shorter, it results in slower water evaporation not only from the growth substrate, but also from the plants themselves. And that is exactly what happens during cultivation under LED. Even if the temperature in the cultivation area is the same (which it should because plants simply need heat), the water consumption would decrease because of the smaller volume of plants. Larger plants consume more water and that leads to more water evaporating into the air. That is exactly the case with sodium-vapor lamps. The logical conclusion is then to decrease the number of plants and amount of irrigation when cultivating under LED modules. Many growers overwater their plants, which leads to a number of problems and a generally poor crop. It is one of the most common mistakes, regardless of the illumination technology used. Many gardeners who switched from sodium-vapor lamps to