Fertilizer NPK Ratios

[QuantumSparky]

So this question is perhaps pretty basic and I have an idea as to the answer if my assumptions are correct, but when someone advises for something like a 9-9-9 NPK ratio fertilizer, is that all in percent volume? For example, 9% of the bottle is Nitrogen, 9% is Phosphorus, 9% Potassium? I assume that it isn't representing an actual ratio because then a 3-3-3 mix would be the same as a 9-9-9 mix which would be the same as a 1-1-1.

So if those numbers instead represent percentages, is the rest of the fertilizer (example being a simple liquid fertilizer) just composed of water?

I'm trying to make sure I understand all of this because I don't have any high strength fertilizer, only a liquid 1-1-1. So if somebody suggests that I use a 9-9-9 then theoretically I should either not dilute it or dilute it much less in order to provide the tree with a more potent dose of nutrients.

Does this sound correct?

 

[Shibui]

Your assumption is almost correct but, like many other things, it does depend where you live.
In the USA and Europe fertilizer ratios are based in the weight of the COMPOUNDS in the fertilizer and should not be read as N:K but as N: P2O5: K2O. Phosphate as P2O5 means that not all of the phosphate in your fert ratio is actually phosphorus. The actual P in your fert is around half the amount stated in the ratio.
In Australia, South Africa and (I think?) NZ the regulations allow for the actual ELEMENTS to be used for the ratio so down here a 10:10:10 actually has 10% N 10%P and 10%K
This site may explain some of the differences: https://www.gardenmyths.com/fertilizer-npk-ratios-what-do-they-really-mean/
Wikipedia has more: https://en.wikipedia.org/wiki/Labeling_of_fertilizer

In the scheme of things those differences don't make a huge difference for the amounts of fert we apply to garden plants so most of us just look at the ratios as the amount of nutrients in the product.

but to the next part of the question:

So if those numbers instead represent percentages, is the rest of the fertilizer (example being a simple liquid fertilizer) just composed of water?

Correct assumption. The remainder of the fert is 'carrier' or impurities - whatever the company has used to bind and spread the actual compounds together or, in organic ferts, the bits that are not nutrients.

I assume that it isn't representing an actual ratio because then a 3-3-3 mix would be the same as a 9-9-9 mix which would be the same as a 1-1-1.

The different ratios show how concentrated the elements are which gives canny buyers a chance to compare value for elements. 1 litre of 9-9-9 contains 3 times as much actual fertilizer as the same size container of 3-3-3. If these were the same price the 9-9-9 would obviously be giving you much better fert value for your $
In most cases the stronger formulation will be diluted more or less used at a time - the 9-9-9 will theoretically last 3 times as long as the 3-3-3

Readers should also note that balanced does not mean equal when it comes to fertilizers. Plants do not need or use the macronutrients in equal ratios so 10-10-10 is actually an unbalanced fertilizer and the plants will not be able to use some of those nutrients you paid. Much better to use a fert that has different ratios that plants actually require.

 

[sorce]

-9-9 then theoretically I should either not dilute it or dilute it much less in order to provide the tree with a more potent dose of

I don't think they would offer different values of the same concentration if this held entirely true. The diluting may result in a different concentration that actually gets to the plant, if at least due to runoff from the extra water.

That said......
There's the legality side, to which you may or may not be abiding by, depending on the application instructions.

Sorce

 

[QuantumSparky]

Your assumption is almost correct but, like many other things, it does depend where you live.
In the USA and Europe fertilizer ratios are based in the weight of the COMPOUNDS in the fertilizer and should not be read as N:K but as N: P2O5: K2O. Phosphate as P2O5 means that not all of the phosphate in your fert ratio is actually phosphorus. The actual P in your fert is around half the amount stated in the ratio.
In Australia, South Africa and (I think?) NZ the regulations allow for the actual ELEMENTS to be used for the ratio so down here a 10:10:10 actually has 10% N 10%P and 10%K
This site may explain some of the differences: https://www.gardenmyths.com/fertilizer-npk-ratios-what-do-they-really-mean/
Wikipedia has more: https://en.wikipedia.org/wiki/Labeling_of_fertilizer

In the scheme of things those differences don't make a huge difference for the amounts of fert we apply to garden plants so most of us just look at the ratios as the amount of nutrients in the product.

but to the next part of the question:

Correct assumption. The remainder of the fert is 'carrier' or impurities - whatever the company has used to bind and spread the actual compounds together or, in organic ferts, the bits that are not nutrients.


The different ratios show how concentrated the elements are which gives canny buyers a chance to compare value for elements. 1 litre of 9-9-9 contains 3 times as much actual fertilizer as the same size container of 3-3-3. If these were the same price the 9-9-9 would obviously be giving you much better fert value for your $
In most cases the stronger formulation will be diluted more or less used at a time - the 9-9-9 will theoretically last 3 times as long as the 3-3-3

Readers should also note that balanced does not mean equal when it comes to fertilizers. Plants do not need or use the macronutrients in equal ratios so 10-10-10 is actually an unbalanced fertilizer and the plants will not be able to use some of those nutrients you paid. Much better to use a fert that has different ratios that plants actually require.

Thanks for the great explanation! I don't know why I had assumed the latter two elements were just molecular phosphorus and potassium instead of oxides, obviously I didn't retain anything from high school chemistry haha. I understand it a bunch more now though after all that

 

[QuantumSparky]

I don't think they would offer different values of the same concentration if this held entirely true. The diluting may result in a different concentration that actually gets to the plant, if at least due to runoff from the extra water.

That said......
There's the legality side, to which you may or may not be abiding by, depending on the application instructions.

Sorce

I view the legality issue as more of a liability waiver for the manufacturer as opposed to a usage requirement for the customer. Unless I own a huge nursery and decide to dilute my liquid fertilizer and create tons of runoff into the water table, I don't think anyone will be knocking on my door

 

[KiwiPlantGuy]

Hi,
You could always buy a CF meter. This measures the amount of soluble salts in your liquid ferts (in water diluted). Readings between 5-15 is in the average range based on once-a-week feeding plants.
The reading is taken in the diluted solution of water and ferts. This gives a mainly correct idea as to whether your brew is too strong or too weak etc.
Hope that is helpful, and it really doesn’t matter what you buy as long as you are not burning roots by being too strong (CF +25).
Charles