Using Jacks 321 in flower

Hey everyone. I have 4 Cherry Pies going in auto pots and have been using Jacks 321. Flipped to 12 and 12 last week. Does anyone add anything else or is there a need to do anything different in flower? Thanks

A lot of growers will bump up part A, and back off part B. A good ratio is 3.8/2.2/1.2 while in flower.


For future reference

Jack’s 321 standard mix & used for veg= 3.6/2.4/1.2

Booster mix= Jacks Part A/ Cal nitrate (Part B) / Epsom salts / MKP

Flower mix= 3.8/2.2/1.2.

If calcium issues try 3.7/2.5/1.1

MKP is Monopotassium phosphate. Available as lots of name brands like Mother of All Blooms, Beastie Bloomz, Flower Fuel, etc.


Curious as to when you make your ratio change? At flip,after transition or when flowers appear?

I go heavy on Part B for the first 4 weeks of flowering to support the vegetative growth of the stretch. I don’t really follow the prescribed amount and instead keep the ratios the same, but go heavy when PPM is low or back off a bit when runoff PPM is high.

It can be difficult to calibrate Part A based on visual appearance, but with Part A I go by leaf color (e.g what shade of green, dark or light.)


Jacks has a bloom booster.
Use it for first 2 weeks of flower.
After that I use 3.6/1.1/2.2 adjust if any negative reaction. :metal:t2::sunglasses:

Im interested in this, ive never varried the ratio and have had good results am woundering if this alteration would make a noticeable improvement and of so what??? Always willing to learn and fine tune.i have added the 3 FF solubles in flower because i had them left and figured wth.

I read many many post about people having to supplement some sort of P K during flower. I liked Jacks for my grow but will probably try something different next go. I had swapped to a more bloom focused nutrient during flower personally.

If leaf is light green, what change do you make? And vise versa.

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Im pretty sure he meant Part B. He’s very knowledgeable at what he’s doing. :v:

If your plant is a light color, it could be a lack of nutes or other issues like pH, light, and or all of the above. It could also be a lack of nitrogen, which you find in part B. So, you might add a little more Part B.

If it’s a dark green, it’s more than likely too much nitrogen which is in Part B. Of corse there could always be other problems but when it comes to Jack’s, that what usually happens. In that case you would lower the amount of Part B you add.

Hope that answers your question. Someone else may be able to explain it better. :+1:t2::v::sunglasses:


Good catch and explanation!!!

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Perfect, thank you.


Look at this picture and tell me how you all would adjust your Jack’s dose. This is Coco Coir and perlite, Jack’s at 3.8A, 2.5B and .99 Epsom pH’d to 5.7-6.0. All of these are at different flowering times with the lighter green just 1 week in flower receiving the exact same dosing.
Based on the above information, I’m think 3.6, 2.5, 2.1 veg and when going into flower, transition to 3.8, 2.2, 2.1. Does this make sense? By the look of the later flowered plants, I’m a bit high on nitrogen.


I personally use jacks 321 in autopots and have been using jacks 321 for the last year and a half

Seedling to veg jacks 321 - 3.6/A. 2.4/B. 1.2/epson salt
I also use silica 2.5 per gallon
And micros as photosynthesis plus at the moment.
When I switch to flower/flip to 12/12 o switch up the ratio
Jacks 222 and 1.2 of mkp
Silica and photosynthesis plus for 3 weeks
Then after 3 weeks back to jacks 321 ,silica and photosynthesis plus…all the way up to 2 weeks before harvest then just water only.
No more mkp after 3 weeks of flower…
Hope this helps happy growing


I’m currently in week 7 of flower

If you need more calcium increase part B
If you need more magnesium then increase epson salt…


I run just about the same. Nice garden!!!

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Ty pin boy
Very much appreciated :+1:

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Can anyone tell me what is going on here. 4 Cherry Pies all growing with auto pots and jacks 321. PPM is around 1000 and PH is 5.8. Flipped to 12/12 on 7/18.
Mixing Jacks at Part A 3.6 grams Salt 1.1 grams and Part B 2.4 grams.
Any help would be appreciated


5.8ph is too low for soil @JohnM …you appear to have a lockout to me. A good flush should reset everything.

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@OldSkunk I am using Coco and perlite