npk when blending water soluble ferts

k0ry15August 4, 2013

Hello everyone,
I wsant sure on where to post this but since all my plants are in containers i figured WTH. I was hoping someone could explain how to determine the final npk percentages if i for example wanted to blend a 3 lb. batch of fertilizer from multiple ferts, such as (ammonium sulfate, MKP, potassium sulfate, iron edta, etc....) Any info would be greatly appreciated.

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There is software you can download to help with the calculations. Without, it is a complicated mathematical process and not sure worth the effort. Why don't you just purchase a formulation close to what you need? The specific numbers are less critical than the ratios but even that is not cast in stone.

FWIW, I use one liquid fertilizer for all my containers - trees, shrubs, annuals, veggies & fruits, houseplants. All are perfectly happy.

Sometimes I think we get a little too involved with fertilizer specifics.......generally not necessary unless you are doing bigtime agriculture.

Here is a link that might be useful: nutrient calculator software

    Bookmark   August 4, 2013 at 6:51PM
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k0ry15, it has been a long time since I have had to do this but here goes!
One gallon of water weighs 8.0 lb. (approx.). If you dissolve 1 lb. of ammonium sulfate in it, the new weight is 9.0 lb.
Ammonium sulfate contains 21% nitrogen.
1 lb. of ammonium sulfate will contain 0.21 lb. nitrogen.
We now have 9.0 lb. of a solution that contains 0.21 lb. nitrogen.
The percent nitrogen in the liquid is; 0.21 divided by 9.0, multiplied by 100.
The solution has an analysis of 2.33 - 0- 0. (NPK)
You can do this for each element and arrive at a final formulation for a blended mixture.
Hope this helps.

    Bookmark   August 4, 2013 at 7:41PM
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thank you for the replies. i've tried hydrobuddy, but im not using a hydro set up. And im not really trying to blend a liquid fert necesarily, but a small batch of water soluble (basically a MG like fert )where i can adjust ratios. I understand that ratios are by weight, but get confussed when figuring in percentages of the salts. Example: Want a 5lb. total wt. 30-10-20 blend using urea, ammonium sulfate, MKP & sulfate of potash. i know 30% of 5lbs(2240 gms) is 1.5lbs(672 gms) of N. If urea is 46% & ammon. sul 21% and i use 336 g of each. it would only give me 225.12 gms of N which is about 10% of the 5lbs. im probably doing this completely wrong but i cant find any info on it except for blending liquid ferts. Again, thank you for the replies.

    Bookmark   August 4, 2013 at 10:56PM
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Gardengal...may I ask what liquid fertilizer you use? I have container veggies.

    Bookmark   August 5, 2013 at 6:59PM
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It's called Liquid GROW by Dyna Gro - 7-9-5.

BTW, it's when you combine nutrients with varying NPK's that you run into mathematical difficulties. Why not locate just a decent turfgrass fertilizer and call it good? These typically offer a 3-1-2 ratio........

    Bookmark   August 6, 2013 at 4:17PM
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prestons_garden(9B SZ 22 HZ 6 SoCal)


Let me know what salts you want to use and the desired ratio of N-P-K.

If I don't respond in a week, email me.


    Bookmark   August 9, 2013 at 11:09PM
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