This is the fifth article in a series where I present some 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 it’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 flushing the plant's medium. This month, I give you...
Franco’s tricks on pH
There are many ways to grow good cannabis; the path each grower takes depends on knowledge, background, and philosophy. Those who dare to adventure off the beaten path, and keep curious about new possibilities, usually end up becoming really good growers. By trying new systems, new mediums, new feedings and new genetics growers can improve the quality and quantity of their output. Due to the illegal status of the plant, there has been relatively little scientific research on how to grow cannabis. On the other hand, there has been abundance of practical experience, as cannabis is one of the most cultivated plants on earth. Trial and error has been the traditional way of learning for the large majority of growers, and only in recent years, thanks to Internet and to cheap air-travel, the cannabis community has been able to link and to exchange information, data and genetics at an unprecedented pace. This has resulted in an explosion of the cannabis industry in general. Soil, hydroponics, coco fiber, aeroponics, organic feedings, synthetic feedings; each system has its positive and negative sides, and each can deliver great cannabis, if done properly.
Of all factors that determine a successful crop the most important are: air, light and feeding. And for feeding intake, pH levels are crucial for optimum results.
A small minority of growers has completely organic operations (meaning they use soil collected from forests, use predators to fight pests, and make their own compost exclusively from organically produced food) where controlling the pH of the watering solution should be done exclusively using lemon juice (to lower the pH) or limestone (to higher the pH).
But most growers use some form of synthetic feeding, so they don't mind using nitric acid or phosphoric acid to lower the pH of the feeding solution, and calcium carbonate to increase it. Most growers need to lower the pH of their feeding solution; it is actually rare to have to increase it. The difference is in the stage of development of the crop. During vegetative growth, nitric acid works best, while during the flowering period phosphoric acid is the most indicated. This is because of the binding that happens with Nitrogen or with Phosphorus already present in the feeding.
But the question always coming back is: what's the right pH?
The answer is easy, jet complicated. The easy part is: safe levels are anywhere in between 5.5 and 7.0.
Cannabis can successfully assimilate most of the nutrients needed when the pH is in between these levels, especially if all other important factors (air, light, watering frequency) are at 100%.
Of course, to optimize quality and quantity it is best that all nutrients are assimilated at the optimum moment. Therefore it is advisable to keep pH around 5.5-6.0 during vegetative growth, and to increase to 6.1-6.5 during flowering. This way the Nitrogen is best absorbed during vegetative growth, and Phosphorus, Potassium and microelements are best absorbed during flowering.
Because of the different conditions and optimal levels, it is worth examining a few typical situations.
In case of outdoor guerrilla growing, it is difficult to control the pH of the earth. The best is to make sure the soil does not contain too much clay. For the rest, the only control is trying to balance well the feeding solution. Best in these conditions is to start at 5.5 pH then move on to 6.5 during flowering, and up to 7.0 during the end of the crop. A high pH at the end will reduce the chance of bud-rot or fungus development.
Indoors, it really depends on the medium and the strains.
In soil, with most indica strains, it is best to start at 5.8 during vegetative growth, move to 6.2 during flowering, and end at 6.4 at harvest. With more sativa varieties it is advisable to start at 5.8 and then smoothly go up to 6.8 at the end of the flowering.
In hydroponics, the trick is to remember that the pH of the medium tends to jump very high very fast. Therefore, it is best to stabilize the pH of the medium at 5.5 before starting the grow cycle, and keep it slightly lower than one would do in soil. Flowering can be done at 5.8-6.0, and the end of the flowering should be done at 6.2-6.3 for indicas, and 6.4-6.5 for sativas.
In coco fiber the game is similar to hydroponics, while in aeroponics the pH should be stabilized between 5.5 (grow) and 6.5 (flowering) for perfect intake.
Adjusting the pH at the right levels will ensure that even the microelements are absorbed properly, which will boost resin production. And will also ensure that the plants stay green well into the flowering, guaranteeing maximum surface available for photosynthesis when the buds are building up.
During my career as grower, breeder and seed maker I met several growers that were able to produce the finest product without controlling the pH of their nutrient solution. But it was cases of serious natural-born green finger. The large majority of growers benefits from controlling the pH and applying the theory to the practice, while remembering that it is always useful to experiment and fine-tune the values to tailor the genetics and the unique environment.
Franco – Green House Seed Co.
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