top of page

PK Boost – The Myth Behind When to Apply it

Updated: Dec 10, 2022

PK boosts are known to add bulk to your flowers, but when applied they can be somewhat deceiving. So, this is not just about when to apply a true PK boost, but also about understanding proper available PK amendments. Lots of blog posts talk about when to apply, but your plants actually tell you when you should be applying, at least a small amendment dose of additional Phosphorus (P) and Potassium (K). This is the same concept as a shortage of micronutrients in all lines. Every nutrient line from every company is short on P & K. It's not that they can't still make phenomenal plants, but it also does not mean it is the proper amounts. Nutrient lines are built for the weakest plant to flourish not the most resilient, heavy-feeding plants. You will see some companies have a heavy feeding schedule as they know they know their base application rates, and to be safe, must be less than optimal.

Many bloom base nutrients also just don't have the optimal available P and K, and we say this because when we amend even a small amount of our Bloom Accelerant PK boost to their lines from day 1 flower (1 mL hydro/daily or 2 mL every other day), we are seeing a noticeable difference in the overall health and quality by week 2-3. As none of the main nutrient lines on the market will change their current NPK values, supplementing additional PK is necessary for that earlier additional quality. We also understand some companies because we are exposing basic truths may up their lines and we will be sure to let them know we appreciate the response.

Just because a product says 5-12-26 does not mean that the 12 P and 26 K are completely available…. it doesn’t. The reality is the availability of salt-based or even many organic top-dressed nutrients can be much less than 50 percent depending on what the P &K are made from and what other products growers might have used to enhance that availability. Not all nutrients are the same. GLB pulls out almost all the salts, down to 0.03% in our PK boost, which makes them truly bioavailable. As mentioned, even a small amendment dose shows a noticeable difference from day 1 of flower. So how is that possible if a grower's base nutrients are proportioned properly and available to the plant? Many are not, but there can be numerous reasons why that is. Also, realize many base nutrients from companies may be used for more than just cannabis plants, that is in part because those base nutrients are not a complete hemp/cannabis formulation.

In addition, just accepting any general guideline on when to apply PK boosts is limiting your plants’ potential. We get it, most growers don’t want to test or find out for themselves what and when to apply to get the best results, they just want a product to work like advertised. The problem is reality and marketing are not always the same. Many growers use a 1-, 2- or 3-part nutrient line and think they are going to get the highest quality flower, again, companies’ marketing and advertising claims are... subjective.

To reiterate, using random PK boost guidelines is not recommended and may be limiting the potential of your plant. Yes, we will probably piss a bunch of growers off, but the quality can be seen, this is not something you need a so-called "team of scientists" working tirelessly for your best interests to try to persuade you otherwise. The basis to the argument is this, if you can apply a PK boost that raises the quality and taste of the flower by adding 1-2 mL per gallon then how is it possible that the plant had the proper amount, to begin with? There are a few possible reasons.

By the way, so newer growers understand, each phenotype can uptake nutrients differently. That is the essence of a phenotype. When growers are pheno hunting, in reality, they are looking for plants within a specific genetic with certain favorable traits or characteristics. All the variances come from how that specific phenotype uptakes nutrients. The better the plant takes up a specific nutrient or micronutrient and can convert those nutrients within the plant, the larger potential for heavier yields or higher secondary metabolites. Why do we talk in terms of potential and probabilities? Growing is a constant, but the growth potential and the actual growth are fluid to all the positive and negative influences and environmental inputs every second of the grow. A bad environment or any other limiting input for even a few hours can kill a plant, so genetics and nutrients are only potential and can only go as far as the grower's ability to control their inputs.

So how do you know what your specific plants need from the start of flower? Subjective marketing or internet blogs and even rates on labels are basic guidelines, not an exact science. If a plant is a heavy feeder, does that mean you just give higher doses of a PK boost during the prescribed guideline week applications, or should you be feeding more from day 1? Many growers assume that the NPK ratios in the grower’s nutrient lines are correct. We tend to disagree, at least when we apply our Bloom Accelerant, there is a difference within the first 2-3 weeks of flower. That being said, there are caveats as to why some products don’t make sense to start earlier as not all products are made to be used from day 1 of flower.

Even though we find that more available PK is needed at the start of flower when amending other companies' lines, we are making assumptions about the other companies products as to why. Is it that other companies' flower-based formulas are not enough intentionally or non-intentionally, probably so. Otherwise, how does our PK boost raise the quality within the first 2-3 weeks? And yes, certain forms of quality nutrients including carbohydrates are prioritized by cells when they are being incorporated into the plant and biological processes. Our organic chemist has not determined all the reasons why there is a prioritization, except to say that we have found that certain forms of nutrients including the removal of almost all salts do play a role in cells prioritizing uptake.

When to use PK boosts is an interesting topic as we hear growers use them in specific weeks, but if you start asking questions, some really don’t know why. Some growers don’t even follow the directions on the products they are using. Maybe it’s all the blog posts like this one that people are getting their ideas from, or they take one set of application rates they used with one product, and apply it to another product? Any post or article that gives PK boost recommendation as a generalized shortened time frame doesn’t make much sense as each product is different and cannot be put into that box. The public never really knows what's in all the products. The grower is either giving enough available PK or they are not.

Most products that are a part of a full line have a specific purpose to be used in conjunction with all their other nutrients, so it may have nothing to do with a certain set of weeks. Growers should invest some time and research before extrapolating a product if not using a company's whole line, unless it has application rates for Individual Amendment Use, and learning how to adjust that PK boost to the recipe a grower is using. It may not be the proper amendment or the best for you if you are trying to Frankenstein a program together of a bunch of different products as something might be missing. All the added products separated out are sometimes for marketing purposes as well so a grower can't easily switch out one item for another item in another line. That's why GLB makes small amendments that work separately without changing a grower's current recipe. It fills in the gaps on growers’ current lines making a better flower.

Some companies add carbohydrates to their PK boost. In that case, many will not add their PK boost at least until the start of week 3 because carbohydrates can stretch internodal spacing 5 plus inches if used from day 1 of flower. As mentioned, some companies may believe they have enough PK in their flowering formula. Some PK boosts have so much salt it’s hard to use from the very beginning due to parts per million of Total Dissolved Solids. The plants just can't handle it. There are several other reasons, but sometimes it seems some companies promote bigger buds strictly with regards to selling more of their separate PK product.

Side note- We DO NOT Believe you should automatically use your carbohydrates in every case from day 1 of flower, as other companies promote. Answer the questions at the bottom of the GLB Brix57 page to determine when you should use from day 1 and one you should use from Day 15 unless you know your genetics and lighting are on point to reduce stretch.

So back to why, for marketing purposes, yes, a part of the fertilizer industry relates to a marketing strategy by companies that many growers don’t always notice, and it has nothing to do with the health of the plant. The later a PK Boost is started, if the base nutrients are not enough, the larger, more noticeable effect it “seems” to have on the flower. It has little to do with how great the product is but is more related to timing and marketing. They know they have an issue and the fix is to add additional PK, if they wait a bit it happens to work even more in their favor. If they advertise better results, they can sell more. So, is the product you are using applied in the best interest of your plant, or what a grower seemingly is seeing in results? Now we are not saying to change what you are doing, just amend what you need.

Hypothetically speaking, as we would never say a company would do this, but for the sake of argument, let's say a company didn't put enough PK boost from Day 1 of flower, that plant would already be limiting its potential but wanting for additional nutrients, then weeks later it is given a heavy dose. We 100% guaranteed the plant would explode and fatten up but was it necessary or healthy for the plant? It's not because of the special sauce in the product but giving the plant something it should have already had.

So, if you should not use general PK Boost guidelines, and products may cause issues if used too soon, or companies are only telling you to add later in part as it shows a better result on the plant, what’s the answer?

Nothing is easy. We are not saying that additional PK later in the cycle is not beneficial. There are ways to start a regrowth for more weight, but that new late regrowth also doesn't finish properly without additional time. It's relative to what proper available nutrients the plant has to uptake. Many companies push a combination of nutrients including PK the last two to three weeks to create a "secondary growth phase". There are ways to make this happen, but we will already be pissing enough people off with this blog so we will leave that for down the road.

However, what we can say is that waiting to apply at least a PK boost amendment past week 1 of flower in most cases limits the potential of your plant. What we have seen is our Bloom Accelerant raises the quality at a faster rate due to having a truly bioavailable amount of P & K from day 1 of flower on a full dose, but even with our amendment doses (1-2 mL) it adds visible quality when used from Day 1. We have seen it constantly, don’t trust what anyone says, test for yourself.

Yes, additional phosphorus and potassium will help in yield, secondary metabolites, and much more. Different companies’ products have visible degrees of quality and yield effect, but adding a PK boost from week 3, or 5 on, to make the appearance that it bulks up plants faster can be just marketing claims. If applied correctly from day 1 "bulking up" starts faster but more gradually through the flowering cycle. The problem with bulking up faster and gradually is, it affects the advertising claims of the massive flower PK booster as they can no longer state how big their buds get by using their PK products over a longer more consistent basis. What we have found is if enough PK is available, among other nutrients, genetics determine the size of the flower. The more the genetics can handle, the larger the flower. The differences between the products are finding out what is the most available amount of PK boost needed to give the plant the proper amount of P & K without causing additional ppm and salt issues. One of our growers is pushing his genetic to 3.9 EC and the plant could still handle more. The caveat, some companies are putting in other undisclosed items in their products, but those same results can be seen without all the mystery or hefty price tags.

On another note, this post is about other product lines and the lack of proper available P & K, we are not advocating for entirely switching out a grower's current PK boost for our Bloom Accelerant. Just add over the top of your current recipe and make it better before changing again to a bunch of new products. We are just talking about adding the proper smaller amendment to what's missing in your current grow. Our belief is the goal should be to apply nutrients to allow for the best quality, not for marketing purposes.

Regarding quality, let's be clear, holding back or not making available the proper amount of PK earlier in flower is not a manual low stress that somehow helps the plant with the highest levels of photosynthesis. Depriving the plant in the early stages of flower does not create additional terpenes, or other secondary metabolites, like low-stress training techniques or intentional stresses applied at the end of flower. Giving a plant less than what they want is just limiting possible potential earlier in the cycle.

So what purpose is there to not giving the plant what it needs when it wants it? Many companies don't want to make another separate PK boost to fix their base as they are selling growers on sometimes 7,8,9 plus products already. We can't say why companies don't give enough available P & K. What we can say is all companies know that all plants are not getting the highest efficiency of PK and micronutrients from day 1. They are not trying to make toxicities in some plants by pushing them too hard. But holding phosphorous and potassium back from a plant that wants it on day 1 flower is not allowing that plant to cycle its photosynthesis properly and at the highest levels. Again, we will make the point, many companies believe the amount they are giving their plant is the proper amount in their flowering recipe, and it’s just our Bloom Accelerant because of its availability which is making the difference, but either way, the plants want proper available P and K sooner than later. The first two weeks of flower is when vegetative growth is still occurring and one of the weakest points for its immunity during the entire cycle, making it more susceptible to pest and disease problems as well.

Photosynthesis is directly related to up to 95% of the biomass of any plant. As we give our cannabis plants a higher PK Boost from day 1 of flower with our Bloom Accelerant, we see the flowering process visibly start faster with secondary metabolites increasing in the first 2 weeks of flower. This is especially true when using our PK boost at a full dose. A grower can have the best genetics and nutrients and not be able to grow an average plant because they can’t control their environment. It’s not just about the flowering processes starting sooner, or bulking up faster in smaller increments, but it progresses over the entire cycle to reduce unneeded additional stress and be able to layer higher levels of secondary metabolites.

We mentioned it in a few places on our site, but we don’t believe there are magical products that grow bigger plants. Zero products create bigger buds, that’s marketing, maybe we just have a different belief in how plants grow. Your plant has maximum potential in the grower’s environment using specific genetics and nutrients. The moment a seed is placed into the soil, or even before a clone is cut from a mother plant the potential is limited. Every input, which includes all stresses, limits the growth of the plant. Growing a seed in a paper towel rather than soil, neither is right nor wrong, but what works best for the grower in their environment. However, each decision is either positive or negative for maximum growth and is specific to the grower’s environment. If a grower can't figure out cloning that is a limiting factor. When a product is introduced to a plant that contains nutrients, trace minerals, or biology that allows the plant to grow closer to its potential, it’s not magic in a bottle. It has nothing to do with making a plant bigger, it may seem that way, but products are just inputs. It has to do with removing a limitation. If a product removes stresses or gives the plant an available nutrient it was not getting before there can be significant growth, but all the product did was remove a limitation. It's a subtle difference, but advertising claims that products make massive buds are just not true.

And side note, we are not talking about synthetic PGRs that may enhance yield but significantly reduce quality through reduced secondary metabolites. GLB does not deal with anything that would reduce quality and all those PGRs reduce quality. Growers using synthetic PGRs give up something to gain in another area, and that’s more of a business decision. If you use a product and the plant grows bigger or there are other benefits, but the quality of the plant goes down, do research on that product as they may be hiding synthetic PGRs in it.

Many growers do not realize that the start of the flowering is one of the weakest points during the entire cycle. The quality of a grower’s plants is constantly changing based on environmental, nutritional, and biological inputs. A plant can be in perfect health but due to several factors the plant can be reduced to a weakened state at any time even for a few moments and that is when insects or diseases take advantage of the situation as well. Why would anyone growing medicine for themselves or others, want to hold back the proper amount of nutrients from a plant that helps in part to protect itself at such a critical stage?

But back to the PK boost, what we are talking about is common sense folks, if a plant can be healthier by feeding the proper amount of PK sooner, why wouldn’t a grower do it? Can you honestly say every product you use you can see a difference in the plant? What’s the quality of that difference? How come so many growers switch out one set of salt-based nutrients for another or PK boosts for another, but don't see any real change in quality.

Our Bloom Accelerant is a 0.5-17-17 PK Boost with 0.03% salts. We use it as an amendment or full dose but in either case, we recommend at least testing additional PK from day 1 of flower to see if your plants need it. If your PK boost has 0.03% salts and the majority of your flower stems from P and K, it's not just an assumption but will be proved in the final product that it just tastes better. For those that are used to harsh-tasting flowers, even the amendment dose will raise the quality and smooth out that experience.

Why do we start the PK Boost Day 1?

Several reasons, but the internal research shows that our plants uptake our PK at higher rates in the first two weeks with less of a stress load on the plant. As we are not limiting the plant of P & K, it allows the plant to cycle properly, which directly and indirectly relates to a higher Brix level in the plant. This does not mean that there cannot be a boost during the later weeks, but by giving the plant what it wants when it wants, we create a healthier plant. By extending out the feeding we do not condense the stress during those few weeks, which allows our plants to start to stack on trichomes and other secondary metabolites much sooner as well. If you add our Bloom Accelerant later in the cycle for a few weeks, would you see a noticeable bulking? Yes, of course, but why reduce the plant’s potential by limiting basic nutrients that the plants want, which then affects cycling photosynthesis at its highest levels?

Amendment Dose Bloom Accelerant PK Boost 0.5-17-17

Hydro/Daily Feed 1 mL per gallon

Every Other Day 2 mL per gallon.

Grease Pack #2

Every Other Day per gallon -- (Daily or Hydro Feed is 1/2 these rates)

0.5 mL Enhance MC Microbial

0.2 mL GLB Micro DS

2 mL GLB Brix57

2 mL Bloom Accelerant

In early 2023 we will have our BloomSap 0-9-11, which will combine 60% of the fulvic acid from Enhance MC, as well as the equivalent of the Micro DS, Brix57, and Bloom Accelerant into 1 bottle. This will be for commercial grows and those that are just starting out using our nutrients without having to measure out all the products in week 2 flower until flush. We do recommend using it from Day 1 for a number of reasons including getting the PK boost started but some will still want to start Day 15 for the shorter nodes and bigger-looking bud structure.

Photos from top down by @Mr._General.G, @WeTheStash_, @NewGen_Hydro, @SweedBeeCo,@Mr._General.G

1,039 views0 comments

Recent Posts

See All


Commenting has been turned off.
bottom of page