Nkp combinations

Hi guys, not sure if this the right category or even a stupid question but I can’t find what I’m looking for to wrap my head around… I think of it as stoner math :rofl:

Here’s a picture of the best way I can explain. If you took 3 fertilizers with different nkp and combine at different strengths, what would the final nkp value be? Maybe im over thinking this, but it seems like an important thing to understand ! The nkp values shownare the ratiosfrom packaging and says percentage


We wouldn’t want to combine different products that aren’t meant to be combined because the chemistry can cause elements to fall out of solution, resulting in an unpredictable NPK

If you understand the chemistry, you can figure it out. But you can’t assume 5-5-6 + 10-15-2= 15-20-8


Sulfides, Chlorides and Phosphates (The various forms of nutrient suspension) don’t mix
well and can potentially lock out availability to the soil and plants from within the medium.
The reaction of the mixed fertz will happen within the soil and potentially ruin the soil

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You can mix and match with organic dry amendments though you just add the numbers then divide by amount added like a unit of12 0 0 and a unit of4 8 4 makes 8 4 2 per singular unit measure

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Hi, seriously thanks for your input. This is definitely a fictitious formula I made up to try and understand better. The it’s listed as percentages and not ratio by volume so I figured there wasn’t any math… just needed to hear it from you guys.and Im no chemist for sure lol.

You may have saw my other post but I was struggling with my first grow. Made a bunch of mistakes but I think its under control and i have a better plan for next grow using jack’s A and B. It’s on it’s way.

For right now, unfortunately, all have is a couple types of mg (18 18 21and 24 6 16) Flower Fuel 2 34 32 Its a long story but I’ve used some mg 24 6 16 and the plants are looking alot better. Im just entering flower stage, so my plan was to use the flower fuel with tapering down amounts of 18 18 21… :man_shrugging: Im in depleted, 6 week old FF Happy frog. I had a slight nitrogen burn early before I should have added any nutrients and i just properly figured out ph a few days ago it was a bad plan from the get go obviously.

Do you guys think I can mix those 2? I’ve got some cal mag on the way too. Plus as I mentioned the jack’s a and b is on the way but probably not for another week or so. Not sure either of those will help this grow or how I would use them. So I’m limping along :rofl: There’s a Walmart near by but not sure what fertilizers they have in stock to help now.

Everyone on all my posts have taught me a ton!! I appreciate all the help and sorry to keep mumbling on about my first grow. Right now I don’t have alot else going on either​:rofl: I would’ve replied sooner but I didn’t get the usual email telling me I had replies lol… I just figured everyone laughed and moved on :grinning_face_with_smiling_eyes:

Thanks again

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thanks @PhillyRock I appreciate the response

thanks @GreenSnek appreciate the input. First grow :laughing:

Not much of a soil guy here but if you are planning to run Jack’s 321
Part A
Part B
Then you need to get some Epson salt.

Sorry if you already know all this.

I use:

Armor si .5 tsp/gal
Part A 3.69 grams / gal
Epson salt 1.2 grams / gal
Part B 2.44 grams / gal
Hydroguard .5tsp / gal which you may not need in soil (??)
Mixing in that order.

Good luck! :v::+1:t2::sunglasses:

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If you added equal parts what would the final ratio of n to p to k be?


Thanks bud, I did know about the epsom salt. I can get that locally. But I appreciate it anyway. The Armor i had not heard of but I have considered the hydroguard. Maybe I should have ordered that instead of cal mag…

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You can put any numbers into the example and it remains true. You can’t assume 15-0-5 + 0-15-10= 15-15-15. You can’t assume 5-5-5 + 5-5-5= 10-10-10. Again, those numbers reflect plant available nutrients, but they don’t hold up when we mix product lines and/or varying the order of operations set out by the manufacturer.

Did that answer your question, or did I miss your meaning?

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Does not answer my question, because I was taught npk ratio stacks just like that, pretty much the opposite of what you’re saying. As in ratio weight by volume, regardless of whether they are necessarily plant available or not.

Edit… I guess I understand what you’re saying to an exact. The potential for one element to bind with another and bring it out of suspension. But this is limited application, and the reason we have mixing instructions correct?


I think we’re in exact agreement; the molecular composition totals of two combined solutions are additive. I’m most concerned that two soluble components of a solution will precipitate out of the solution. I’m somewhat less concerned that the cations and anions will remain suspended but react to become less available.

You’re correct about following instructions. I’m pointing out that there aren’t usually instructions for mixing products from different manufacturers. And often, we can’t mix products from different lines from the same manufacturer. By “can’t” I mean not without trial and error to create our own mixing instructions, or a grasp of the chemistry involved.

So even if I come up with an SOP to make my own solution, based on successful grows, I’m not going to assume it’s replicable if I swap out products for something else with an identical NKP.

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I bet you could be successful if you switched to using the raw compounds over bottles/bags of hydroponic nutrient mixtures.


As a way to save money, or exert more control?

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Both really.

It’s not something for everyone, but all you are doing by paying for blends is having someone take a portion of the work out. If you check ingredients on bags/bottles they are all basically using the same stuff. Hydro buddy can help, and if you look around the web you can probably even find recipes for copycat mixtures.

When states like Washington and California required fertilizer companies to post all the info people doing this came out of the wood work. I have dabbled in it a little, don’t really have the time. But it’s not very difficult for people with reasonable understanding.


Part of what I’m paying for is the analysis Peter’s does. I’m also assuming they get huge wholesale discounts, and pass enough on to customers that it’s hard to beat their pricing.

I’ll definitely check out Hydro Buddy. I’ve also got a few friends in local commercial hydroponic greenhouse work; I’ve never asked what they use.

My current grow is so small though that I’m stocked with Jack’s 321 for 20 years.


I found both parts and the bloom online, but I can’t find the finish. Have/do you use the finish? I understand that the 2 parts and epsom salts are enough… so are the bloom and finish worth it? Sorry if I already asked this :sweat_smile:

I’ve been satisfied with the results from A, B, and epsom salt alone. Different genetics are going to want different things. I think some people add a silica source, and I know some people switch to a bloom formula for a two week period starting at the switch to 12/12.

Thanks Keystone, next grow will be just the basic and maybe do something extra for following grows to learn the differences