Lefthand Jacks with Peters - Hydro Experiments in 5-1X-26

Since it seems that people have interest in custom nutrient experiments, I’m going to log some experiments I’ll be doing amending a 5-1X-26 formula. In theory, this applies to several popular hydroponic formulations, including:

Peters Professional 5-11-26
Masterblend 5-11-26
Southern Ag 5-11-26 (blue razz)
And also Jacks 5-12-26 – much like the 5-11-26, but with negligible differences in P, and more significant differences in Mg (uses more epsom than the other formulas).

As a personal note, as long as I’m adding epsom, I prefer the 5-11-26 formulas so that I can provide other sources of Mg (primarily Magnesium Nitrate), and also epsom is already cheap and easily available. Note that Peters’ now lists their mix as having 6% Mg, similar to Jacks. It used to be 3.2%, so be aware of that difference and adjust accordingly.

For those interested in following along, pick your 5-1X-26 poison. I’m currently using the Southern Ag formulation, which I call blue razz, because it’s a startlingly artificial blue color. This is due to the use of copper chloride in the formulation to provide copper. I don’t prefer it because it’s more hygroscopic/clumpy than Peters, but sometimes it’s cheaper to purchase.

My Base Mix (control)

  • Southern Ag 5-11-26 (3.2% Mg)
  • Yara Calcium Nitrate 15.5-0-0
  • AgSil 16H (diluted to 1% mixture)
  • STS Super Shock (for reservoir sterility)


I’m going to use very inexpensive amendments. The goal is to minimize costs, so I won’t be using any fancy bottles. Here’s what I’m amending:

  • Fertilome 9-58-8 (MAP/MKP)
  • Monopotassium Phosphate 0-52-34 (MKP)
  • Magnesium Nitrate
  • Epsom salt (Magnesium Sulfate)
  • Peter’s STEM micronutrients
  • Potassium Sulfate 0-0-53

First up, the 9-58-8 is a simple mix of MAP and MKP that balances N/K while boosting P. This stuff is very cheap – I think that the 1.5lb tub cost me $9 at my local garden store. My target application for this is rooting (early growth stages). Next up I have MKP, which is a standard PK booster. I will be targeting flower/bloom stage with this nutrient. STEM is a broad spectrum trace element supplement. Finally magnesium nitrate I will try as a replacement for epsom during veg (as in my coco thread).


Bloom experiments are a little more challenging, and I’m not willing to sacrifice my grows, so these will be a little more conservative in approach. Typically, I’ll be using MKP, potassium sulfate or combinations thereof.

Veg experiments are where I’ll focus most attention. Intermittently, I plan to do more rigorous scientific experiments, possibly even to the point of killing plants due to nutrient imbalance, but still using conservative mixes for seeds I care about.

I’ll conduct nutrient “boundary tests” to determine their upper limits. This will look something like:

  • start ~10-20 seeds from my pile of randoms
  • germinate and plant into treepot with measured weight of rockwool croutons
  • amend base mix with test nutrient, while controlling EC
  • weigh plant mass and root mass after a standard period of time
  • repeat experiment to increase amendment until deficiency is caused

Qualitative experiments on plants I do not wish to destroy will also be performed. Currently, I’m starting with this mix in veg:

Standard 321 base mix, Fertilome 9-58-8 (ratio 1/10th of the hydro mix 0.3 ratio), Agsil 1% solution, 1.0EC. Fixed flood and drain cycle of once per 12 hours. For roughly 20 gallons, I used:

30g 5-11-26 blue razz
20g Calcinit
10g Epsom
3g 9-58-8 Fertilome
15mL 1% Agsil 16H
2g STS super shock

The hypothesis is that P is used more heavily during early stages for promoting root growth. @8k_feet saw some P deficiency at colder temps in his basement, possibly implying that the base mix could be amended with more P during early growth to provide a better tolerance to low temperatures, or to increase root mass.