You end up with 2 tbsp of 17.5-10-10 or close to a 2:1:1 ratio. Mix a little potash into your soil and you're good to go for maters. Use your end product based on the rates suggested for the 20-20-20.

Al

Thanks Al, but I am looking for the math to get those numbers. I randomly chose the values in the above post. Hook me up! Thanks for the feedback...

Al, I think that one of 2 things happened here, either you made a mistake, or I am doing this wrong. I think it is probably the latter, however, I do not know where I messed up.

I get 3 TBSP of a 18.3-6.7-6.7 or a 2.75:1:1 ratio. Since you said 2 TBSP, I thought maybe you missed that it was 2 of the first and 1 on the second, but if I use that I still don't get your numbers. I may be underfeeding some of my plants as a result, so if you could help me know how to do that calculation correctly, I would appreciate it.

Also, would that be a little strong for all of that to go into just one gallon? Once again, I must be thinking too weak when it comes to fertilizing. I better correct my thoughts before I underfeed all season!

Thank you in advance, Barb

Just to confirm...I will not be fertilizing with the above mix. I am just looking to understand how to do the math for a combination of two fertilizers in varying amounts. Thanks again!

Bogaat, I know that now, but I was typing and calculating at the same time, and had the posting window open way longer that I should have, and as a result did not see your post (10 minutes before mine). Sorry for the confusing order of postings, my fault!

Barb

I did miss that it was 2 of 1 and 1 of another.

Technically, I took a shortcut and assumed that the fertilizers had the same bulk density and that equal volumes of these fertilizers weighed the same. That makes it easy when you are adding the same volumes of each fertilizer. Add up the % of each element in each tablespoon and then average them. For N > 20+20+15=55 55/3= 18.33% For P&K > 20+20+0=40 40/3= 13.33% So your NPK %s are 18.3-13.3-13.3, or close to 3:2:2 ratio.

For fertilizers that aren't very close in bulk density, you have to figure by weight instead of volume, which requires another step or two.

Al

Al, thank you for that. But I see that your P,K is 20+20+0 each. Shouldn't it be 10+10+0 using the example in the beginning of this thread? I am not trying to be difficult, just need to know, cause most fertilizers are P2O5 and K2O, and those 2's in there are making me wonder.

Here's to beating a dead horse! Barb

Lol - Ok. (friendly poke in the ribs - don't slap me for being familiar!) ;o) If you want YOUR P and K reported as ACTUAL P and ACTUAL K, multiply the P% (or weight) by .43 and the K%/weight by .83. Otherwise the numbers are correct. I'm going to prolly confuse you now by telling you to ignore the 3:1:2 ratio when considering ACTUAL P and K - if you were shooting for something different but based on some deviation from that ratio. If using %s of the actual elements, you'll want to vary the approximate ratio 6.7:1:4 to achieve your ends.

Al

OK, Al, this is scary, because I think I understood you! I was poking around with a spreadsheet after your 15:55 post, and I actually came up with a 6.9:1:3.8 ratio for ACTUAL P,K for the 3:1:2 "as sold" ratio. Not far off of your number above! I had to dig deep into the recesses of my memory for terms like moles, molecular weight, etc.

At the risk of continuing to monopolize this thread, but on a related topic, the reason that I have such an interest in this is that I wanted to take a 1.5 pound box of MG 24:8:16 with minors and make a concentrated solution, then use the more accurate measurement of liquid measurement over granular. I find that as the season progresses, my fertilizer becomes clumpy and less accurate to measure. My target is to dilute to approx 300 ppm N for fertilizing. If I take the whole box and mix to make 2 liters, I could then use 2 teaspoons of concentrate per gallon and achieve 304 ppm. This is assuming 2000 mL of water, which would likely be less when actually measuring. Of course I would measure the actual amount of water, and this would then drive up my concentration, forcing me to reduce the 2 teaspoons. (If the actual water portion is 1500 mL, then the 2 teaspoon/1 gallon example would be driven up to 499 ppm)

I have been wanting to try this for years, but never sat down to work out the numbers until today, which is why the interest in this thread.

Thank you for indulging my obsession! Barb

No problem ....... but you need to keep concentrations high enough to prevent bacteria that love the N from growing and fouling the solution. Sorry, I can't tell you how high that concentration needs to be.

Al

I never thought of that, you have a point. Although, with 1.5 pounds of fertilizer and less that 2 liters of water, I imagine it would be harder to grow something in that than in the Dead Sea. Of course, I do not know going in if the fertilizer would stay in solution, so I may have to weaken the concentration, which may make the whole "easier to measure" motivation get offset by the "where am I going to keep all this stuff" dilemma. And then your point becomes even more of an issue. You may have changed my mind. Thanks for the feedback. Barb