Topdressing: Easy way to make a custom fertilizer mix with dry meals, including how to adjust NPK

Cola-C

Well-Known Member
Topdressing dry meals in a organic soil grow is the ultimate in kick-back feeding for plants. If you build your own soil mixes from scratch, you're gonna have a lot of leftover ammendments. Want to make a custom mix using a multitude of dry meals like : alfalfa, kelp, neem, fish bone, chicken manure pellets, guano, etc? Want to recreate your go-to fertilizer mixes at a fraction of the cost?
I'll show you how I make my own fertilizer mixes, and teach you how to manipulate those NPK values.
You might not care about NPK, but using the same ingredients you're already using in your grow but tweaked for nutrient ratio isn't going to hurt, is it? Cycling additions is always a good idea, and switching topdressing amendments through the season will do just that.

Equipment:
All you'll need is a variety of meals, some measuring cups, and a kitchen scale. I used some typical meals used in organic gardening.

- Quick explanation:
NPK values are based on % of mass. Most soil recipes are based on measurements of volume (cu.ft, gallons). I took my unit of measurement (1Cup), which is a measure of volume, and weighed 1Cup of each of my meals to get the mass (weight).

Approx. weights of 1Cup of meal/NPK values:
Alfalfa - (5oz) 2.5 - 0.5 - 2.5
Kelp - (7.5oz) 1 - 0.1 - 2
Crab - (7oz) 4 - 3 - 0
Neem - (6.5oz) 6 - 1 - 2
Fish Bone - (8oz) 3 - 16 - 0

Now multiply each value in a given NPK by the weight in ounces.
Ex. - Alfalfa weighs 5oz in a cup. N 2.5 x 5 = (12.5 ) P 0.5 x 5 = (2.5) K 2.5 x 5 = (12.5)
Do that for each meal.
Now add all the N values together. Then P and K.

The above values totaled:
111 - 158.75 - 40.5
Now add up the total amount of ounces:
5 + 7.5 + 7+ 6.5 + 8 = 34oz
Divide each NPK value by 34:

= 3.26 - 4.67 - 1.2
N P K
I'll use that for VEG.

For BLOOM I'll soften the nitrogen and even up the P and K numbers while adding sulfur and magnesium. I chose to use Langbeinite 0 - 0 - 22 aka sul-po-mag. I'll take 1 Cup of the above fert mix and add 1/3 Cup of Langbeinite.

So as before I'll weigh the 1/3 Cup of Langbeinite = 5.3oz

Follow all the steps before and multiply the NPK values by oz then add all the values together and we arrive at:
111 - 158.75 - 157.1 ÷ total oz (39.3)
=
2.8 - 4.03 - 3.99
N P K

You can see how different inputs will have an affect on the final NPK values. All you have to do is adjust the use of each ingredient. Hope this helps
- ColaC
 

The3rdMan

Well-Known Member
I found something similar on a Grass City forum and it has been extremely helpful in calculating NPK of my own custom mixes for both Veg and Flower. I would encourage others that like to make their own soil mixes to take a little time to learn this.

Regarding your NPK for a Veg mix, is 3.26 - 4.67 - 1.2 adequate? Should N have the highest number? For flower, you have P and K about the same?
 

ExoticKangaroo

Well-Known Member
This is pretty cool. Ive been wondering how to incorporate langbeinite into my grow. My local grow shop guy recommended it to me but he was so blazed he couldn't explain anything to me lol.
 

Sup Im BirDy

Well-Known Member
Topdressing dry meals in a organic soil grow is the ultimate in kick-back feeding for plants. If you build your own soil mixes from scratch, you're gonna have a lot of leftover ammendments. Want to make a custom mix using a multitude of dry meals like : alfalfa, kelp, neem, fish bone, chicken manure pellets, guano, etc? Want to recreate your go-to fertilizer mixes at a fraction of the cost?
I'll show you how I make my own fertilizer mixes, and teach you how to manipulate those NPK values.
You might not care about NPK, but using the same ingredients you're already using in your grow but tweaked for nutrient ratio isn't going to hurt, is it? Cycling additions is always a good idea, and switching topdressing amendments through the season will do just that.

Equipment:
All you'll need is a variety of meals, some measuring cups, and a kitchen scale. I used some typical meals used in organic gardening.

- Quick explanation:
NPK values are based on % of mass. Most soil recipes are based on measurements of volume (cu.ft, gallons). I took my unit of measurement (1Cup), which is a measure of volume, and weighed 1Cup of each of my meals to get the mass (weight).

Approx. weights of 1Cup of meal/NPK values:
Alfalfa - (5oz) 2.5 - 0.5 - 2.5
Kelp - (7.5oz) 1 - 0.1 - 2
Crab - (7oz) 4 - 3 - 0
Neem - (6.5oz) 6 - 1 - 2
Fish Bone - (8oz) 3 - 16 - 0

Now multiply each value in a given NPK by the weight in ounces.
Ex. - Alfalfa weighs 5oz in a cup. N 2.5 x 5 = (12.5 ) P 0.5 x 5 = (2.5) K 2.5 x 5 = (12.5)
Do that for each meal.
Now add all the N values together. Then P and K.

The above values totaled:
111 - 158.75 - 40.5
Now add up the total amount of ounces:
5 + 7.5 + 7+ 6.5 + 8 = 34oz
Divide each NPK value by 34:

= 3.26 - 4.67 - 1.2
N P K
I'll use that for VEG.

For BLOOM I'll soften the nitrogen and even up the P and K numbers while adding sulfur and magnesium. I chose to use Langbeinite 0 - 0 - 22 aka sul-po-mag. I'll take 1 Cup of the above fert mix and add 1/3 Cup of Langbeinite.

So as before I'll weigh the 1/3 Cup of Langbeinite = 5.3oz

Follow all the steps before and multiply the NPK values by oz then add all the values together and we arrive at:
111 - 158.75 - 157.1 ÷ total oz (39.3)
=
2.8 - 4.03 - 3.99
N P K

You can see how different inputs will have an affect on the final NPK values. All you have to do is adjust the use of each ingredient. Hope this helps
- ColaC
Very nice!! Very informative!! This will help when I make a veg mix and bloom mix for my next grow. Now to dig into some NPK articles
 
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