Q: Regarding combining nutrients and the resulting cumulative strength of solution

[TanR]

Hi all,

First time indoor grower that has benefitted greatly from all the knowledge, experience and insights so generously shared on this site. As stated, I'm new to indoor growing, but not growing our beloved plant. I have searched all the forums and threads for a number of different key words and can’t seem to find anything that addresses my query.

My question is meant to be very general, not specific to any particular phase of growth, age or size of plant, or even a particular growing medium. I will provide a little insight, to help further define my question.

Since this is my first indoor growing endeavor, I chose some really good bag seed to be my test subjects. I am growing all organic in a good self-concocted heavily amended soil based medium. I confess that I have not invested in a “line” of nutrients, but have instead chosen to utilize some products I either had on hand or could purchase locally. When I feed my plants, I do so by adding the nutrients into the water at least a day or two in advance of their next feeding/watering with a bubbler stone in the bottom of the bucket.

With that background providing context for my question; Do nutrients, when combined, have a “cumulative” result?

As an example, say I add fish emulsion that is labeled 5-1-1, then I add another organic fert that is labeled 4-3-3, do I end up with a concoction that is 9-4-4? Obviously, the amounts added would factor in, but in answering please assume I am adding in equal parts or at levels equal to the instructions to achieve the desired results. I also recognize that the resulting “strength” of the brew would be effected by the water and its ability to deliver those nutrients and I am aware that the analysis provided on a label represents only the "minimum" amounts of each nutrient.

I’m just looking for the basic, yes or no to “Do the numbers add together” or are the levels of each individual nutrient limited to the highest value of any one individual ingredient.

Thanks in advance for any insights the community can provide.

 

[GreatLife4All]

Re: Q: Regarding combining nutrients and the resulting cumulative strength of solutio

Hello TanR

You have asked a great question - and unfortunately I can not just answer yes or no. If I did, the short answer is 'No'.

I don't yet have a good way of looking at this using an analogy. But this topic confuses everyone - at least according to my conversations with other growers at the local shop. Everyone seems to believe that you get more nutrients with something like 16-16-16 than you do with something like a 5-5-5 - many of the fertilizer and nutrient companies prey on this ignorance. But in actuality - they can both be mixed to deliver EXACTLY the same strength of nutrient solution. No difference whatsoever in the final mixed product. What you actually get is a HIGHER concentration of nutrients in the package - not necessarily more nutrients in the final mix. If you will - it is simply a more efficient packaging consideration (15% of the total weight is usable fertilizer as opposed to say 48%).

So let me concoct a very generic example - and see if I can not indirectly answer your question.

We have two nutrients we are going to be using NuteA contains 5-0-10 and NuteB contains 0-10-10. We also know that our plant likes a ratio of 1 part Phosphorus for every 1 parts Nitrogen and 2 parts Pottassium - so we want to get as close to that as possible. If we express our desired ratio using the same nomenclature, then we would have something like 1-1-2 as our ideal mixture of these three nutrients. So how do you get 1-1-2 from two mixes, each of which has higher levels? Dilution and mixing, of course.

What exactly does 5-5-5 mean? Here in the US, legally it means that there is a minimum of 5% (by dry weight) of plant usable nitrogen, 5% of plant usable P2O5, and 5% of plant usable K20. The other 85% can be anything - but is typically a water based carrier plus preservatives and stabilizers.

Ok. I am going to skip a bunch of math and formulas to keep this simple. If you want to get things exact, then you have to use conversions for dry weight to liquid, you have to convert P2O5 into something that actually records at the correct PPM, and you have to do the same conversion for K2O - this involves atomic weights, and etc. You would even have to calculate the fact that you increased the water volume from 1 liter when you added NuteA to be really accurate. So rather than record all these details - I am going to simplify the math so that I can calculate this in my head. Your results WILL vary if you calculate this exactly using official formulas - but my results will be within 10%.

So we now know that NuteA contains 5%, by weight, of nitrogen. So if we take a liter of water, add a milliliter of this 5% solution - what do we end up with? Exactly 50 parts per million of Nitrogen in the liter of water. We also end up with 0 parts per million P205 and 100 parts per million K20. So if we use a TDS meter - it should now state that we have 150PPM in our solution. Each of the three nutrients has added to the total PPM of our solution.

So now we take our liter of water with a milliliter of NuteA in it - and we add a milliliter of NuteB to it. By the same analysis that we did previously, We have added 0 ppm Nitrogen, 100 ppm P205, and 100 ppm K2O. Our final solution now has 50ppm Nitrogen, 100ppm P2O5, and 200ppm K20. We pull out our handy TDS tester - and it shows a strength of 350ppm. And what is our ratio? We did in fact hit our ratio of 1-1-2. We have 50ppm Nitrogen present, 50ppm P2O5 present, and 100ppm K20. We also have an excess of P2O5 and K2O.

It was proven long ago that plants use nutrients in ratios. It does no good to bump up nitrogen without also increasing the amount of K2O. Nitrogen in our example is the limiting factor on growth. Even though the solution will read 350 on a TDS meter, only 200ppm of that is usable by the plant. We are wasting nutrients.

No fertilizer solution will ever be a perfect mixture for all phases of growth for all plants. So unless a company tailors their fertilizer solution to a plant - there will be waste. This is one of the reasons that farmers have excess nitrogen - in order to get the correct levels of Potassium, they are forced to put on excess nitrogen which eventually leaches out of the soil and into the waterways (there are other and bigger issues here - and it is off topic, so I won't elaborate). We tend to break a plants life cycle down into 2 phases - bloom and veg. We know that the nutrient requirements are very different (the ratios are different) for plants in these two phases. A fertilizer which has everything required for bloom - would be complete wrong and wasteful for veg.

Now... just to finish this off. What if we take NuteA and mix 1ml into a liter of water. We take NuteB and mix 1ml into a separate liter of water. We now combine the two and what do we end up with? All nutrients will be an average between the two because we doubled the water. So the final mixture ends up with 25ppm Nitrogen, 50ppm P2O5, and 100ppm K20.

I did all this math on the fly and in my head - there could be some mistake in here somewhere. Because I did it in my head, I had to use metric instead of imperial system. There is no way I could calculate using gallons and oz in my head! So if something doesn't make sense, ask and I can either explain or break out the spreadsheets and give you official numbers. I can even convert it to gallons and oz if you prefer...

I know this is rather long - but I don't know of a simple way to answer your question.

 

[TanR]

Re: Q: Regarding combining nutrients and the resulting cumulative strength of solutio

GreatLife4all,

Exceptionally detailed, insightful and educational answer. I confess I had to read it twice, but I think I now have a thorough understanding of your response. I sincerely thank you for taking the time to share the information.

Be well and happy growing!

 

[closetorganic]

Re: Q: Regarding combining nutrients and the resulting cumulative strength of solutio

HIgh TanR
Another No from me! If they are both say dry ferts and equal in wieght on adding together the %N would be <5, and the %'s of P AND K would be more than 1% and less than 3%. So your right on the highest NPK numbers being limits on the miniumum percentage of fertilizer wieght

 

[TanR]

Re: Q: Regarding combining nutrients and the resulting cumulative strength of solutio

Thank you closetorganic. I appreciate you taking the time to respond also. It's so nice to find a community that is so willing to support and nurture one another in our endeavors and education. Truly a gem of a collection of folks!

Be well and happy growing friend.

 

[JJ Bones]

Re: Q: Regarding combining nutrients and the resulting cumulative strength of solutio

Yes they do.

Example: Nutrient A is 2-0-0 and Nutrient B is 1-0-0 this would mean your overall NPK in the reservoir is 3-0-0