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Friday May 21, 2021

By Trevor Ross


Ask ten different cannabis growers what fertilizers they use and how to administer them, and you will likely get ten different answers, but most of them will probably recommend a “boost” of nutrients around the flowering phase of the plant’s life. In fact, these nutrient-boosting products are often marketed as essential or even necessary for a lush, heavy harvest.

Factor this in with every other variable involved in cultivation, and growing cannabis becomes a dizzying prospect for all the wrong reasons. In the interest of simplifying cannabis and making it accessible to everyone, let’s take a more comprehensive look at these “bloom boosters.”

What are Booster Nutrients?

Booster nutrients are nutrient mixes typically administered during the flowering stage of the cannabis plant, and are generally high in phosphorus.  Some even boast an eye-popping 1-34-32 NPK (more on this below). These products claim to induce more and larger blooms on your cannabis plants, resulting in larger yields of smokeable flower.

However, this principle – and these products – are not new, and certainly did not arise out of the cannabis market.

In fact, many farmers and gardeners regard these products with leery skepticism. To understand where this belief comes from, we first need to understand the role of phosphorus in growing plants, including cannabis.

What is the Function of Phosphorus in Plants?

Phosphorus is the “P” in “NPK.” Any fertilizer worth its packaging will clearly state the ratio of the three primary macronutrients with their abbreviations on the periodic table: nitrogen (N), phosphorus (P), and potassium (K).

The nuances of biochemistry are detailed literally down to the molecule, but painting with a broad brush we can say that nitrogen contributes to the growth of everything green, like stalks and leaves; and phosphorus contributes to the growth of everything else, including roots and flowers. Again, this is a simplified statement, but it illustrates why we prioritize nitrogen during the vegetative stage, and why many people swear that more phosphorus equals more flowers.

Someone holding phosphorus
While many believe growth can be acredited to phosophorus, this may not actually be the truth. photo credit

In the insular world of cannabis growing, especially home growing, it can be easy to forget that there were farming practices before weed. Remember, fruits and vegetables grow out of the flowers of their plants or trees, so farmers are very familiar with high-phosphorus fertilizers. And ornamental flower growers have been chasing the biggest bud for centuries. So what do they have to say about the claims of “bloom boosters?”

Per the American Rose Society, “Our passion to give our [flowers] everything we think they need has led garden product marketing departments to create more things we think our [flowers] need… The fact is, high phosphorus levels in fertilizer do not promote more bloom, and it’s very possible these fertilizers may be doing more harm than good.”

That harm comes in the name cannabis growers dread: nutrient burn, and nutrient lockout.

The Risk of High-Phosphorus Fertilizers

Adding too many nutrients to your soil or water can quickly result in nutrient buildup, when high concentrations of fertilizers chemically burn the tender roots of your plant.

Additionally, everything you do to your soil or water nudges the pH up or down. There are a dozen plus nutrients and minerals that plants feed on, and each nutrient has an optimal pH range of bioavailability – the nutrient’s availability to be absorbed by the plant. For example, phosphorus is absorbed more at a lower pH (acidic), while potassium is absorbed better at a higher pH (alkaline).

Soil Nutrient Lockout Chart
This "Nutrient Lockout Chart" can help growers to understand the absorbution of various nutrients for a cannabis plant. photo credit

The ideal pH for cannabis is between 5.5 and 6.5 because this is the range where nutrient uptake is most balanced. Moving up or down from this range may make one nutrient more available, but at the expense of others. When these nutrients are present in the soil, but not being taken up by the plant, it’s called nutrient lockout. 

The result is the same as underfeeding, and no amount of additional fertilizer will help.

How to Boost Cannabis Flower Production

It is true that plants can benefit from increased levels of phosphorus in the flowering stage as opposed to the vegetative stage. However, to reliably and consistently increase your cannabis yields, a holistic approach should be taken from the beginning of the process, not just at the flowering stage.

Fertilizer developer Aaron Hoare spoke with Maximum Yield in 2018 arguing just this point. Hoare regularly analyzes the parts per million (ppm) of macronutrients in his runoff water, which accounts for nutrient buildup over the whole feeding regimen. Using that data, he arrived at a ratio of 7-6-12 during the flowering phase – a stark contrast to the 0-50-30 being marketed to growers.

His point is that fertilizing elements will accumulate in your soil throughout the whole growing process, so piling on huge amounts of fertilizer at the flowering stage is at best putting a hat on a hat, and at worst, harming your plant.

Are Booster Nutrients Worth It?

Booster nutrients do contain essential elements and minerals for your plant’s health, but sometimes in dangerously high doses. These products are often marketed to new growers eager to buy volumes of various products they’re told will help their plants. The bottles are bright and fun and make promises we want to believe. And sometimes they may even keep those promises.

Bundled products like the popular Fox Farm trio can be great for novice growers who are not using any other fertilizers. They come measured and dosed with instructions on the label, like brownies from a box. But they also assume your growing process will stay inside that box. If your plant has any unexpected issues, nothing on the label will help you.

For growers trying to hone or advance their craft, a more holistic approach will prove more profitable. Take close care of your plant from day 1, and you won’t need a surge of fertilizer on day 50. And if your plant is suffering on day 50, that surge of fertilizer probably won’t save it.

What do you think about using booster nutrients for growing cannabis? Chime-in in the comments!

Photo Credit: RossHelen (license)


Trevor Ross Trevor Ross

Trevor Ross is a writer, medical marijuana patient and cannabis advocate. He holds an MFA in writing from the School of the Art Institute of Chicago. He has previously worked as a copywriter, a teacher, a bartender, and followed Seattle sports for SidelineBuzz. Originally from Washington state, you can find him now working in his garden or restoring his house in Scranton, PA, and he can be reached through LinkedIn.

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