Marijuana Grow Nutrients Guide: The Advantages of Bat Guano and More

Plants at the Rx Green Solutions research facility.
Plants at the Rx Green Solutions research facility.

Ask three cannabis growers for their thoughts about nutrients, and you’re likely to get three different answers. As with green chile and grilled cheese sandwiches, everyone has their own recipes for growing pot, and everyone thinks theirs is the best. Do you go strictly organic, using tea and bat guano to naturally enrich your cannabis? Or do you pump up the nutrients every week for swollen buds and enhanced aromas?

The arguments are old, but the variables are newer. As legal marijuana advances around the country, so does the science surrounding it.

Just ask Todd Brady, founder and CEO of Rx Green Solutions — a hydroponics nutrients company with a cannabis-focused research facility in Denver. “A lot of the products cannabis growers are utilizing today were not made for cannabis plants,” Brady points out. “They were made for ornamentals and flowers and other types of plants, and a plant is an accumulator of the ingredients it’s fed.”

Nutrient companies have generally stayed away from developing products for marijuana because it’s still illegal federally, driving growers to use nutrients that weren’t made for cannabis, instead feeding their plants cadmium, mercury and other heavy metals that people shouldn’t be smoking. A process called flushing, in which the grower feeds the plants only water — no nutrients — during the final two weeks before harvesting, should rid the plant of the metals some nutrients leave behind, but the procedure isn’t always done properly. That’s where Brady feels that his company can help.

Instead of the near-twenty-plus types of supplements that some grows use on a single crop, Rx Green Solutions uses just two bottles of nutrients specifically made for the grow and bloom stages (four overall), making the application easier and reducing the risk of burning — a symptom of overfeeding in which the leaves curl inward and potentially lose mass.

“We try to educate people and teach them how to apply it themselves,” says Leandro Mano, director of Rx Green’s research and development. “You need to know what’s going on inside your plant.”

Which nutrients are best, and how much is needed?
Which nutrients are best, and how much is needed?

Studies on growing conditions, like the ones that Mano (who has a degree in agronomy and a background in biotechnology) heads up are relatively new. Fertilizers for cash crops such as corn, wheat and tobacco have all undergone rounds of testing by research firms and universities, but the book on marijuana nutrients remains essentially unwritten. And some growers don’t care if it stays that way.

Jared Caezza says he has been growing medical marijuana for himself and several patients for ten years and doing it organically for the past four. After making the switch and noticing the changes in both taste and quality of the final product, he gave away all his old nutrients.

“You don’t get the microbes in hydroponic grows that you get in soil. Soil is alive. And the level of terpenes and terpenoids is much higher if you stay organic,” Caezza says. “The smells and tastes have been better since I stopped using pre-made nutrients, and my patients don’t worry about smoking unflushed pot.”

By using natural fertilizers like Jamaican and Mexican bat guano (bat poop) for phosphorus and nitrogen, he explains, he’s eliminated the need for pot-specific growing nutrients — but that doesn’t mean the growing process is any easier. “It took me a few tries to get the soil down, and each batch takes about thirty days to mature. It takes patience. Brewing my own compost tea is also a never-ending learning experience,” he says. “The nutes made it easy. Everything came ready to add in water. But if you want peace of mind, you have to do it yourself.”

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Even Brady admits that buds produced by organic grows are sought out by connoisseurs because of better taste and smell, but he maintains that his yields are higher and the nutrients he uses harmless. And while Steven Newman — professor of floriculture, horticulture and landscape architecture at Colorado State University — doesn’t research marijuana (and says he can’t until its schedule-one status is revoked), he says that plants take in the same nutrients no matter how natural they are. “I have no knowledge of any traditional hydroponic fertilizers, organic or conventional, as being toxic for human consumption,” Newman says. “Whether they are classified as organic or conventional is determined by the degree of processing and/or manufacturing.

“The plants take up the nutrients required regardless of whether [they’re] organic or conventional,” he adds.

So where do commercial growers fall in this debate? Such growers have got to consider the number of consumers they serve, as well as the quality and production standards that those consumers expect. John Andrle, owner of Denver dispensary L’Eagle, says that basic nutrients are a necessary part of the industry, and while organic grows are a model to strive for, they just don’t make financial sense for most commercial grows. “Fully organic grows require an insane amount of human labor, which is expensive,” he says. “It’s obvious to me that the general mood of the cannabis industry is to make money, not spend money making healthy products.“

Although Andrle acknowledges that overfed cannabis is probably prevalent in the legal market, he says there’s a much bigger issue to worry about in the growing process: “What is becoming apparent is that growers are overly reliant on synthetic pesticides. If I had to choose between pot that was full of residual nutrients or pot with trace elements of dangerous pesticides, I’d take the nutrient-laced pot every time. I think there are happy mediums between clean and toxic. The balance boils down to [the fact that] nutrients are basically just salts — nitrogen, phosphorous and potassium — while synthetic pesticides are…who the hell knows what?”

If you’re paranoid about smoking nutrient-laced pot, be sure to take notice of what smoking certain buds do your body. If your throat burns and your eyes water after inhaling some chemical-tasting cannabis, you might want to throw it out — or at least double-check with the grower.


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