Promix is stellar stuff when amended. I have been very pleased with a water only preparation using equal parts promix and coco, plus fine-mdm grade pumice (and dust). That gets amended with dolomite (extremely important for pH buffering the peat and adding Ca/Mg to keep the coco CEC in check), alfalfa meal, rabbit/alpaca litter compost, EWC, and pre cooked super soil mix. Each plant is started in a small net pot until bristling with roots then transplanted to a 2gl square, heavy dvuty, Styrofoam cooler for either automated drip or capillary mat.
Aside from routine watering, they only get a biweekly compost/recharge tea and top dressing of a bloom blend plus gypsum at flip. I use straw mulch or clover companian to help keep the bene’s happy and hydrated. The clover makes a nice environment for my army of lady bugs and mites to chill out in as well. RO reject water is blended back to the permeate until I measure around 150-200 ppm with pH 6.0 ± 0.2. This has hit some home runs for me in both yield and quality.
Promix is sphagnum peat moss, coir, and perlite… never really had problems mixing it with the FFOF…
Random tidbits in no particular order:
Jack’s 321
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The actual recipe is 3.6g hydro, 2.4g calnit, and 1.1g epsom which = 150N.
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Conveniently, a literal 3g ,2g ,1g recipe is about 120N or roughly 80% strength.
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Check out https://kootmed.com/.downloads/FEED/JACKS-3-2-1.pdf
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Jack’s 321 is actually a phased, multi-component system. https://www.jacksnutrients.com/online-store/Jacks-321-p101469431
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That system is clever. You feed 321 @ 150N through veg, then you feed the bloom boost (same stuff as blossom booster Amazon.com) for 1-2 weeks at flip, then back to 321. The blossom booster at their feed rate is just loaded over the top with phosphorus. The roots and shoots accumulate the P and then you can get away with less P through flower. I still add MKP.
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https://www.jacksnutrients.com/_files/ugd/3230c0_15ef9a140f114133bb1be94c8e6ad079.pdf
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Towards the final weeks you feed the “finish” mix. This is simply a low N, high K formula.
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I have pretty hard tap water. Even so, I still add solution grade gypsum and amend promix with extra gypsum. 321 does not supply enough calcium, no bones about it no matter your water/media, especially if you’re modulating/hinging on a lower N target.
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Mix the 5-12-26 hydro and epsom at the same time, then add calnit. There’s already some epsom in the 5-12-26 so mix together.
ProMix
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BX is fine, HP = BX plus more perlite. HPCC is HP but with part coco and I just shy the heck away from coco. (Sorry).
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Yes go with the added mycorrhiza.
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Say BX is the most dense, and HP is less dense… HP is still 70% peat. I personally like to use 50% peat, so I amend my promix HP with vermiculite. It’s mostly about how often you want to water. I could go maybe 3 days in BX, 2 days in HP, and every day in HP50. I just made up HP50.
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Ok all this about promix and pH. Here is the deal. Promix has added lime to buffer the medium (they call it medium not media), and the peat is naturally acidic. The general thought is that “feed pH doesn’t matter in promix” and that’s true, to a certain point. Above something like 230 ppm calcium carbonate in your tap water, PTH states that promix cannot control the pH of the medium over the full course of a bedding plant or cannabis plant run. You’d then need acid injection.
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Promix needs a few days after wetting to get to a decent pH. Prep water pots day(S) before transplanting. I don’t bother, and my plants probably suffer? They like it.
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The amount of ammoniacal vs. nitrate nitrogen directly impacts medium pH direction. High nitrate (over say 90%) will have the medium pH rise for the entire run given average tap water. Jack’s 321 is basically 100% nitrate… This is a real concern for promix growers going longer in the container, where pH just keeps ticking up. To battle this, Jack’s does offer a high ammoniacal formula called “tap” of all things. Ammoniacal sends medium pH down over time, due to two independent factors. Don’t go over 30% ammo, says recent science. Jack’s “Tap” is 20%.
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Secret; add a dash of Jack’s citrus blend to your 321 program to introduce some ammoniacal, if desired of course. A 20% ammoniacal target is roughly 1 gram of citrus per gallon, replacing 1g of the part A hydro. Just, buyer beware that method will alter N target to 180 while slightly lowering all other macros.
I’ll edit if I think of more.
I pull 2 or 3 handfuls of “crap “ out of 1 big bale , always do . In last 3 months I have used 3 bales , all had crap in them, one a stick as big around as my finger 
Killer summary of the latest tips for 3-2-1, bookmarking this for reference!
I never have that much. I wonder if different areas get their pro mix sourced from different places
Super informative, thank you so much 
Anyone else care to share how they feed their promix or your experience with jacks 321?
Don’t use Jack’s, but lots of good info here. I did use Prom is HP, now just peat and perlite with some lime. I use GH Lucas formula. When I use it up, I might switch.
I usually feed over the course of a couple hours. Good enough.
Figured the Pro-Mix HP recipe would spark some thoughts:
For a DIY Faux-Mix you might want to add a wetting agent. Peat is a bit hydrophobic at low moisture levels. A wetting agent will help distribute the salty water more evenly rather than find preferred low-resistance drain paths within the peat. This might not matter if you don’t dry the pots back too significantly, but if you do a few hard drybacks, the wetting agent is a great assistant.
Some use yucca powder, some use “JWA” which I found a little page for on build-a-soil:
-Wetting Agent – BuildASoil
Edit, that wetting agent JADAM link is for foliar applications. I have no idea how it would perform in a peat based medium and only realized this when I double-checked my link.
Here is a link for yucca, which is to my knowledge the defacto powdered wetting agent for peat.
@LD50 That’s great thanks man
I’m running jacks 20-20-20 and promix bx with great success 
I was just thinking I add yucca powder as a wetting agent. I actually use a little every 2 or 3rd water/feed. A tbsp in 5 gallons works great. Diamond K water soluble gypsum with that mix every few days too.
I totally agree a good wetting agent/surfactant is needed with peat.
Good stuff!
This type looks best for mixing into your soil/peat.
I like to add my yucca to my feed water.
I use a hydroponic grade yucca.
Dissolves pretty easily for yucca.
I also hate to pay to ship water.
I’ve got where I add my yucca to a qt of water. Mix my Si in my recirculating barrel. Burn one and by then the Yucca dissolves. After the Si dissolves is when I mix in the Diamond K gypsum.
Glad I’m not the only one 
This thread reminds me I need to order some backup. Check inventory in general for basics.
Never tried Jacks. Please update. I am using Third Eye Organic Soil, and a mixture of Stoned Dust, URB and sprinkle in a little Bud Candy. Stopped Using Botanicare once I started using URB.
I’ve been using jacks in Promix for a couple months for my moms and I am struggling to understand what going on with my runoff ph/EC. I am feeding at 1.6EC and PH 5.8 and my runoff is just over 1.0EC but the ph is freaking 8.2. I did not amend this Promix HP. I understand it has like added, but I wouldn’t expect it to rise so much. I would love any clues or help on that one. Plant seems OK I just don’t understand what’s going on.
What is the date on the bag of Pro-mix?
How hard is your water in terms of either total hardness or % calcium carbonate? Or is this RO water?
What is the % ammoniacal content of the nitrogen you’re feeding?
Are you watering to runoff? How much? Especially critical if less than say 20% of the pot size. So if you have a 1 gallon nursery pot you’ll want to see around 2-3 cups of runoff or more.
- If the date is somewhat fresh, fill another cup with the same amount of promix and water with the same water but zero nutrient inputs. Water daily to 20-50% runoff. Track the pH for that week. Get a trajectory. That will be of most use here.
Edit: Quick references:
When they say:
- " Reverse osmosis units are not necessary for most water sources if the fertilizer is properly matched to the water profile and the crop grown."
They are referring to the % ammoniacal vs. % nitrate of the fertilizer.
And to really send it home, Jacks 321 is NOT matched well to Promix HP as-is. Too much nitrate.