Silicon-based fertilizer supplements are easy-to-use additions to your feeding program that bring numerous benefits to cannabis gardens, including increased crop quality, strength and resilience. Their ingredients—the raw materials in the bottle—are also simple: They’re predominantly bottled silicates. There’s no mystery to silicates or how they deliver silicic acid* to the roots. Nevertheless, some fertilizer manufacturers get the science behind silicates—and the advice they give to growers as to which type of silicate they should use for best results—just plain wrong.
Indeed, the misinformation is so prevalent that we recently published an Emerald Harvest white paper on silicon supplements aimed at correcting misleading claims about silicon-based fertilizer supplements.
Here’s a case in point: On February 7, 2020, an article pushing BioNova Silution, a silicon-based fertilizer supplement, was published on Global Garden’s website. Now, we have nothing against BioNova Silution. It probably works just fine. But what we do know is that some of the claims made in the article and on the product’s label about how and why it works are incorrect, based on the product’s guaranteed analysis and derivation statement as well as publicly available scientific data. Let’s see why.
What’s the claim?
The article and the product description on the label claim that BioNova Silution isn’t just potassium silicate but rather some kind of stabilized and bioavailable† form of silicic acid. They also claim that it contains fulvic acid.
What’s more, the section of the article about silicic acid versus potassium silicate states that “silicates are not available to plants [and] bacteria must convert it to monosilicic acid.” The assertion that bacteria must convert silicates to monosilicic acid is baseless; the author provides no evidence to support it, nor can we find any.
What’s in BioNova Silution?
Luckily for growers, fertilizer companies are required to provide a guaranteed analysis on the product label that guarantees what is in the bottle. When we interpret the BioNova Silution guaranteed analysis, we see that the aforementioned claims made in the article fall apart:
- The derivation statement, which documents the sources of essential and beneficial plant nutrients in BioNova Silution, lists potassium silicate, boric acid and zinc chloride. These are the compounds actually in the bottle. This takes down both the first and second claims in the article: Not only is the product just potassium silicate, but it doesn’t contain any guaranteed amount of fulvic acid.
- Furthermore, in addition to the minimum percentage of essential plant nutrients claimed in the guaranteed analysis, 1.45% silicon dioxide (SiO2) is listed as the so-called non-plant-food ingredient‡ derived from potassium silicate. So BioNova Silution does not contain an innovative or little-known ingredient that is more stabilized or bioavailable than anything else on the market. According to this part of the label, it contains potassium silicate.
Unluckily for growers (in this case), the rest of the BioNova Silution label muddies the waters. The product description doesn’t mention potassium silicate, instead stating that the product is “based on stabilized silicic acid and organic fulvic acid. This special stabilized mono silicic acid, is the only form of silica which is fully bio absorbable to plants. Because the molecule chain has been separated into mono Silicic Acids, every part of silica is 100% available! [sic]” We reemphasize also that the derivation statement doesn’t list fulvic acid or humic acid.
What’s actually going on here?
What “special” stabilized silicic acid could be the source of monosilicic acid in BioNova Silution? The answer is, of course, potassium silicate, because that’s what’s listed in the derivation statement. And this makes perfect sense: Potassium silicate, although far from special (many silicon-based fertilizer supplements are potassium silicates, including Emerald Harvest Sturdy Stalk), is a stabilized source of silicic acid. Potassium silicate, the most soluble silicate salt, is known for its beneficial properties. When mixed in solution, it results in the controlled release of potassium ions and silicic acid—specifically, monosilicic acid. It can be used in both hydroponics and soil because it remains stable regardless of the growing medium.
Now, monosilicic acid, which they mention on their label, is in fact the only plant-available form of silicon. But it is highly unstable. You cannot bottle silicic acid in a solution higher than 100 to 200 ppm. At higher concentrations, it falls out of solution and precipitates as silica (a.k.a. silicon dioxide). Silica, or silicon dioxide, itself is inert and cannot be absorbed by plants. The only way to achieve greater concentrations of silicic acid is to use a counter ion such as K+ or Na+ or Ca+, which traps silicic acid as a silicate. It is the potassium silicate in BioNova Silution and other potassium silicates that yields monosilicic acid for the plant to take up, along with some extra potassium.
That’s not to say silicates are the only way to get silica into your plants. Silicic acid can also be stabilized and made available to the roots or leaves using an agent like choline and polyethylene glycol. However, this technology is comparatively new and, in any case, this form of stabilized silicic acid is not what BioNova Silution lists as the source on the label; again, it lists potassium silicate.
The terminology surrounding silicon compounds can be a bit confusing, but here are a few points that will help you decode marketing gimmicks about silicon-based fertilizer supplements:
- A silicate (e.g., potassium silicate, calcium silicate, etc.) is the compound in the bottle.
- Silicic acid—specifically, monosilicic acid—is what is absorbed and transported by the plant.
- Polymerized silica or silicon dioxide is what gets deposited in plant tissues after transport. It’s also what delivers the plant benefits.
In our white paper Inside Silicon Supplements: Making Sense of What’s Inside the Bottle, we set the record straight regarding silicon supplements: what they contain, which form of silicon can be absorbed by plant roots and the silicon compound that delivers the actual benefits to plant tissues. Take a look at the full paper for an in-depth look at the science behind these fertilizer supplements.
* Silicic acid and monosilicic acid are often used interchangeably. To be precise, silicic acid is a broader category that includes monosilicic acid, disilicic acid and other oligomers.
† By “bioavailable” we mean that the roots and, in the case of foliar application, the leaves can take up/absorb the compound into the plant.
‡ “Non-plant-food ingredients” are beneficial—but not necessarily essential—plant nutrients and other compounds.