Jack's 321 for Autos?


Growing GG4 autos in soil - HF/OF blend, SF2000. Wanting to switch my nutrient line from FF Trio to Jacks 321. Need advice on how to administer these nutrients. On the Jack’s Nutrients website, there is a feeding schedule that is designed for photoperiod plants.

Several questions come to mind.

  • Does a feeding schedule exist for autos? If not, any advice from those who’ve successfully used this line on autos?

  • I’ve been using a blend of RO water and tap water in a ratio of 10 cups RO:6 cups tap. The tap water addition allows for smoother pH control of mixed nutrients. The Jack’s 321 pdf makes mention of adjustments needed based on water quality. I’m not sure what to make of this. Any advice on this? How about feedback on my use of the RO/tap blend of water?

  • I’ve discerned from reading past posts on Jacks 321 that I only need Part A, Part B and some Epsom salt. I hope this is the case as the full set of nutrients is pricey. True?

  • A little confused on the implied solution strengths listed in the pdf. There is a specified ratio of grams/gal for both Part A and Part B solutions that apply to both the vegetative and flowering stages. I don’t understand why these would not differ based on the changing needs of the plant as it goes into flowering.

  • Lastly, there is a Target EC listed for each plant stage. I assume this is the EC of the mixed solution, and not the runoff EC, but am not sure.

I do appreciate any feedback. Always get great advice here.


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Yes Jack’s is fine with auto


Recognizing the PPM of your tap water is likely what they are talking about. If you have tap at 300 PPM and want to achieve 1,000 PPM in your feed, then your target should be 1,300 PPM.

Yes, true.

Most growers feed the recommended amounts each time.

Measure and react to the runoff PPM.


There is no one and done nutrient solution that will 100% cover 100% of the plants you grow. Doesn’t really matter if they are auto, photo, or tomato. If you grow long enough you will run into plants that are sensitive to nutrients or maybe even environmental conditions that require more or less feeding. The recipe provided are general guidelines and some tweaking may be required. Since every grow is a little different, you will absolutely run into some who say you can feed full strength no problem and some who say they feed less.

Going to depend on what’s in your tap water ane how much of it. I would say take a look at total ppm of your water mixture ppm. If under 200 ppm probably wouldn’t worry too much about it.

In most cases this is plenty to sustain healthy plants and have a successful grow. You may find some ways to make targeted improvements on the base recipe, but absolutely do not need to go out and buy everything they list.

Full strength jacks 321 in completely stripped water will come out to around 950ppm. Several of us have ran successful grows feeding this exact solution to plants from start to finish. As mentioned above, it’s completely reasonable to need to increase or decrease a little here. But that’s going to be the case no matter what you use. The needs of plants don’t really change as much as made out by some. Your environmental conditions can have just as much or even more impact on this. For a new grower to be successful usually takes having a reasonable plan and then just watching plants and adjusting as necessary.

Until you get a feel for being able to look at plants and identify needs i would monitor both. Your runoff will trend up if you’re feeding more than necessary and trend down if not feeding enough. Much like many of the soil growers use to determine wheb to start feeding their plants.


:point_up_2: yep, words to grow by :love_you_gesture:


Thank you for the extensive and useful feedback, dbrn32. :point_up_2: :ok_hand:


I use jacks too and grow autos, i recommend adding recharge or mammoth p along with the jacks regiment.

Happy growing!

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