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Fertilizer, NPK, requirements for Cannabis

farside05

Plant of the Month: Dec 2018, June 2019
I did look at the AN study results in the calculator tab. Perhaps i'm not reading it correctly? but to me it seems like there was a 50% increase in demand of P and 41% increase in demand of K during flowering compared to Veg? I'm not disagreeing with you that increasing P will not increase the amount of budding sites or bud quantity, but i'm thinking it has an effect on the quality of the fruit/flower. More than just that, i just want to play around and see how it goes, learn, adapt.. improve.
I don't plan on running super high PK numbers. Your calculator is tremendous help. I would be lost without it. I'll keep reading more about MegaCrop and NPK in general.
thanks again :)
I wouldn't focus too much on % change. Look at the actual numbers that comprise that. The Bloom numbers are:
11800025500128000

Now lets reduce by the common Factor. We get a ratio pf 4.6-1-5. Now lets look at what's already in Mega Crop. 9-6-17. From one of the previous posts, now lets adjust the P & K values to the true amount the fertilizer provided. We have to multiply P by .43 and K by .83. We get 9-2.6-14. Reduced to the common denominator 3.5-1-5. Comparing the first ratio to the second, 4.6-1-5 to 3.5-1-5, we see that we're a little low on N if anything. If you feed up to the 4.6 the plant desires N wise, (ie feeding to keep the foliage the correct Mega Crop Green) then you'll have an excess of P & K, and that's with the base product at the plants highest demands. What would be the point of adding more than the plant can use? The excesses only build up in the growing media and cause issues, or if flushed/watered till good runoff, it just ends up down the drain.
 
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farside05

Plant of the Month: Dec 2018, June 2019
Further...

Look at another fertilizer. We'll pick on Dyna Gro Foliage Pro at 9-3-6. Adjust the P & K and its 9-1.3-5. Reduced to the common denominator 6.9-1-3.8, for simplicity we'll call it 7-1-4. Looking at our 4.6-1-5 "optimal ratio in bloom", we'd see we're over on N and under on K. With this fertilizer we could use a "booster" to realign our 7-1-4 and make it closer to the 4.6-1-5 the plant is looking for. The short of it is, Mega Crop already has the booster built in the base product.
 

rippedcb

New Member
6.9-1-3.8,
I wouldn't focus too much on % change. Look at the actual numbers that comprise that. The Bloom numbers are:
11800025500128000

Now lets reduce by the common Factor. We get a ratio pf 4.6-1-5. Now lets look at what's already in Mega Crop. 9-6-17. From one of the previous posts, now lets adjust the P & K values to the true amount the fertilizer provided. We have to multiply P by .43 and K by .83. We get 9-2.6-14. Reduced to the common denominator 3.5-1-5. Comparing the first ratio to the second, 4.6-1-5 to 3.5-1-5, we see that we're a little low on N if anything. If you feed up to the 4.6 the plant desires N wise, (ie feeding to keep the foliage the correct Mega Crop Green) then you'll have an excess of P & K, and that's with the base product at the plants highest demands. What would be the point of adding more than the plant can use? The excesses only build up in the growing media and cause issues, or if flushed/watered till good runoff, it just ends up down the drain.
:adore:

That's why I tagged you guys :) way more experience and knowledge than me. You see, i went about looking at that study very different way. Instead of focusing on the absolute numbers, which i felt would be relative to so many variables (plant age/size, light, ph, environment..) i figured everything else kept the same, the percentage increase of demand would be a better indicator of nutrient needs than absolute numbers. Your arguement makes comeplete sense and thank you so much for taking the time to explain all that.

So by your arguement, MC is TOO high in P (especialy) and K for flowering? Instead of increasing P/K, if anything we should be increasing N a bit? Never knew demand for N was that high after stretch.. i thought i was being overly generous feeding 125ppm of N during flowering.

This is what went in my res last night.. prior to reading your explaination, but i don't think i'm way off..
4x MC (9-6-17)
4x Cal/Mag (2-0-0)
1x sweetCandy (0-17-28)
2x silica (0-0-3)
my numbers according to your spreadsheet are:
N: ~125
P: ~55 x 0.43 = 23.65 =~ 25
K: ~240 x0.83 = 199 = ~200

Thus 5-1-8 .. So not low in N by anymeans, even @ 4gMC, safe with P.. a little high on K (exactly what i wanted, before i read your post)

Do you feel that would cause issues? how would you tweek it? I can see how MC can cause a buildup of P and K over time if people keep overfeeding. Is it because of it being amino-chilated? i mean, typically its obvious when you are over feeding and your plants will let you know in veg, somehow people aren't noticing overfeeding?

last thing.. i keep reading about this "Mega crop green" are plants on megacrop of a different shade? i'm only aware of healthy plant green and plants deficient/toxic of nutrients green.
 

rippedcb

New Member
Nevermind my last post.. your calculator already takes in account the conversion factor.. so my math above is wrong. I fed 5-2-9 .. so way too low in N, or too high in P/K as you stated in your post. But my current grow is in its last 2 weeks of flowering, so i'll be fine. I need to figure out this for the next grow though. I'll finish the current grow with my current zillion part liquid nutes.. :17:
 

farside05

Plant of the Month: Dec 2018, June 2019
You'll be fine. It's very difficult to not "overfeed P" since most fertilizers have more P than necessary. Just be aware that you could potentially see a build up of it if you don't feed to significant runoff each time or do a periodic, what I like to call, rinse of the medium. I don't necessarily feed to significant runoff each time because to me, that would just be a waste of nutes. Instead, about every 4th water or so, I run a gallon or two of straight tap at them (assuming 5 gallon pot), and then come back with a gallon or two of nutes on top of that. That gets you good enough runoff to clear any nute build up in the growing medium and "reset" things. Of course, in a true hydro setup, things don't build up, its just there if the plant wants to eat it. If it doesn't, then things get unbalanced, and that is solved with the next res change, and you don't have to "rinse". Changing the res becomes the equivalent of a "rinse".

"Mega Crop Green" isn't a color that is specific to Mega Crop only. Some of us like to refer to it as "verdant". It's a nice medium shade green, not too yellow (lacking N) or too dark (forest green meaning too much N). As long as you feed to the point of medium green, there is enough P & K in the base product to take care of any P & K demands in any growth stage. By formulating the product in the manner they have, GLN is basically having you over feed, P & K in veg so that you have enough of it in bloom without having to switch products. Hence why I think it is important to periodically rinse your medium.
 

rippedcb

New Member
@farside05 having a little issue with your calculator. I'm not handy with excel at all so i don't know how or what to do. Anyways, having 2 issues:
1) comparing 5g/gal MC numbers to your calculator, everything lines up, except for ZINC (should be 0.78ppm instead of 78ppm), which is way off and it throws all the numbers off.. See screenshot below:
1581700611368.png

1581701887238.png
 

rippedcb

New Member
the second issue i'm having is with cal-mag. According to the calculator; 5ml/Gal Cal-mag (i'm using the same as you) should be about 102ppm.. whereas, when i add 5ml/G i get closer to 200ppm (500 standard)
1581702096039.png
 

rippedcb

New Member
So i was able to edit/update the numbers in excel to match the new formula of MC and everything else, but still the numbers don't add up to same.. i don't know which calculator to trust lol. @MrSauga if you can help?
 
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MrSauga

Photo of the Month: Sept 2018, Nov 2019 - Member of the Month: Feb, Dec 2019
i don't know which calculator to trust lol. @MrSauga if you can help?
I don't use his new spreadsheet yet but let me tag him again.. sometimes he misses the call :)
@farside05
 

rippedcb

New Member
I think @farside05 @MrSauga the calculations are wrong in the spreadsheet. I used an online calculator for just cal-mag at 4ml/Gallon and i get 168ppm.. which is what my ppm meter was reading at home last night. See below:
1581723665361.png
 

MrSauga

Photo of the Month: Sept 2018, Nov 2019 - Member of the Month: Feb, Dec 2019
I'll go snag a copy now and see what I can come up with. I would imagine farside will have it figured out before I get through it though.
 

MrSauga

Photo of the Month: Sept 2018, Nov 2019 - Member of the Month: Feb, Dec 2019
I noticed the above image you don't have a value for the P in the sweet candy and the K is incorrect for your version of sweet candy...

(0-17-28)
 

rippedcb

New Member
I noticed the above image you don't have a value for the P in the sweet candy and the K is incorrect for your version of sweet candy...

(0-17-28)
The above image (calculation) is just for Cal-mag.. as you can see, all the other rows are 0. Farside had older numbers on the spreadsheet for SC that i didn't bother changing to show you that even just Cal-Mag doesn't add up to ppms (that screenshot is of using his online googlesheets calculator).

But this spreadsheet has taught me what i needed to learn, i can use online calculators to figure out my recipe now. It was just a nicely laid out spreadsheet. Wish i was handy with excel to be able to edit and fix it. Maybe farside can?

what's the specific gravity of MC do you know @MrSauga ?
 

MrSauga

Photo of the Month: Sept 2018, Nov 2019 - Member of the Month: Feb, Dec 2019
what's the specific gravity of MC do you know @MrSauga ?
I'd have to look around. I think someone posted it before. Hang tite.
 

MrSauga

Photo of the Month: Sept 2018, Nov 2019 - Member of the Month: Feb, Dec 2019
OK so this is what I use and the same as what someone else posted so I would go with that. I think farside uses a different number for his weights.

A US teaspoons is 6 grams so the specific gravity was 1.2. Not sure if that's what you were looking for.
 

MrSauga

Photo of the Month: Sept 2018, Nov 2019 - Member of the Month: Feb, Dec 2019
So looking at it the difference is in the conversion factor. Since he uses that for MC, Calmag and Sweet Candy etc it may be that he needs to make differnt conversion factors for each.
He'll let you know what needs to be done but if I'm correct he'll probably separate the conversion factors in this case.
 

farside05

Plant of the Month: Dec 2018, June 2019
Sorry guys, my mom passed unexpectedly this AM. I'm going to be indisposed for much of the next week and won't be looking at any numbers.
 
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