This is the seventh article in a series where I present selected tricks and advanced growing techniques. My name is Franco, and I work at Green House Seed Company, in Amsterdam, since the year 2000. Over the last 10 years I have learned from Arjan countless tricks and advanced techniques, and I developed a few of my own as well. And now itâ€™s time to share some of this knowledge with growers worldwide. If we share the knowledge, everybody wins.
Last month I explained some of the best tricks for growing large outdoor plants. This month, I give you...
Francoâ€™s tricks on flowering indoors
The flowering is one of the most rewarding phases of any crop, because the progress towards the harvest can be looked, touched, smelled. Plants are now developing flower clusters, and there are several factors that can guarantee success in quality and quantity.
Indoors and outdoors, the goal is for plants to feel good about the conditions, the environment, and the grower.
When working indoors it is important to notice that every single factor depends from the grower, there should be nothing left to chance. The ideal climate conditions for flowering at lamps on are at temperature between 25 and 30 degrees Celsius, and a relative humidity between 40% and 55%. When the lamps turn off it is normal that the temperature lowers to 20-22 degrees, while the relative humidity climbs to around 60%. If the temperature gap between day and night is larger than 8-10 degrees Celsius there is a risk of slowing down the metabolic of the crop. The relative humidity must stay under 70% to avoid mold and fungi in the crop. A good way to cope with high daytime temperature is to run the lamps opposite to daylight. This way the maximum temperature in the growroom will stay lower, but the disadvantage of this system is that the gap between day and night temperature will be reduced to a minimum, and sometimes this can create problems because plants actually benefit from a 8 to 10 degrees gap between the day temperature and the night one. Nevertheless, it is better to sacrifice the day-night gap, than to end up with temperatures over 35 degrees Celsius in the growroom during daytime.
Air conditioning is a very expensive and environmentally unfriendly option, but sometimes itâ€™s the only one for indoor growers in warm countries. The benefits are cool air and a drying effect as well, ideal during flowering. It is worth noticing that plants do not like air conditioning directly blowing towards them, it is much better to direct the flow of air towards the ceiling, where it will precipitate allowing warmer air to climb. This way the diffusion of cooled, dry air is uniform in the room and not direct on the plants.
Once the climate is perfectly under control, it is worth dedicating some energy to optimize feeding intake. During flowering the plants use mostly P, K and Micros to produce buds and resin. The N intake is still important during the first few weeks of flowering, but later on it must decrease, or the buds will get leafy and the calyx-to-leaf ratio will decrease dramatically, creating issues for manicuring as well. Only with extremely long-flowering sativas, the N intake can be kept a little longer, to avoid premature yellowing of the leaves. To allow plants to slowly intake less N and more P-K-Micros, the pH of the feeding solution should stay above 6.0 after the beginning of the flowering, ideally slowly climbing between 6.2 and 6.6 in soil, and slowly climbing between 5.9 and 6.3 in hydroponics, depending on the strain and the stage of flowering. The rule of thumb here is that the more a strain is long-flowering, the higher the pH should be at the end of the flowering process; with 12-weeker sativas pH usually climbs to 6.9 or 7.0 at the end of flowering. The most important of Micro-elements (Mg, Ca, Zn, Fe) are also assimilated at best if the pH is above 6.0 and these are very important in the formation of terpenes, cannabinoids and resin.
The best way to make sure the plants intake the available minerals is to ensure that they are hungry and thirsty. The best is to create a cycle of dry-wet medium, where the dry spells allow plenty of oxygen to the root sytem and the wet spells allow enough watering solution to be absorbed. The one thing that flowering cannabis plants do not like, is a constantly wet medium.
Besides the normal watering cycle, it is also important to regularly flush the medium to get rid of salts. This can be done with a mild solution at pH 5.5 and EC 1.0, so that the salt crystals can bind to the low-mineral-content in the solution and dissolve. Flushing should be integrated in the regular watering cycle, and after flushing the medium should be allowed to dry properly before feeding again.
Once the feeding is optimized, it is good to take care of the other factors affecting a successful crop. Between them, supporting the flowers, and optimizing the pre-harvest and the harvest. After 4 weeks of flowering the plants have usually developed enough bud to start getting heavy, so it is advisable to support the branches with some system (bamboos, elastic bands, nets, yoyos or any system that prevents branches from collapsing under the weight of the flower clusters). Depending on the strain, support can be an important or a marginal issue. Large sativas usually need the most support.
Pre-harvesting means removing most of the large fan-leaves from the plants during the last days of the flowering cycle, before cutting them down for manicuring and drying. Pre-harvesting helps reducing the total amount of green material (water and chlorophyll) in the crop. Once the big fan-leaves (the ones that have no resin on) have been removed, the plants reduce the amount of photosynthesis, and produce less starches. This allows for sweeter and better-burning weed, and makes the whole harvesting process much easier and faster.
In conclusion, it is up to the grower to identify the weakest points of the grow, and improve from there. Curiosity and will to improve are the key factors to a green thumb. During flowering, a lot can be done to ensure a great crop; and itâ€™s all worth it.
Franco â€“ Green House Seed Co.
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