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Jack's 321 feeding schedule and calculator

Jack's Nutrients' official 3-2-1 schedule for pure water, scaled to the water you're mixing. Three powders, weighed in grams.

Checked Oct 20, 2026 Source: Jack's Nutrients Nutrition Schedule: Jack's 3-2-1 One Gallon (cannabis and hemp, pure water sources)
How to read a feeding chart Schematic of a 12 week feed chart. Each week shows the label dose as a dashed outline, a solid start at 50 percent, and a gold work-up band to 75 percent. Veg weeks 1 to 4, flower 5 to 11, flush week 12. FIG. 01 · READING A FEED CHART SCHEMATIC, NOT A BRAND CHART Label dose, and where to start LABEL 100% WORK UP 75% START 50% 01 02 03 04 05 06 07 08 09 10 11 H₂O 12 VEG · WK 1 TO 4 FLOWER · WK 5 TO 11 FLUSH
01

Mix calculator

Pick a week and how much you're mixing

Many growers here feed below the chart. Start low and raise it only if the plants want more.
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Turn on JavaScript to use the calculator, or read the full schedule below.
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The full schedule

Grams or mL per gallon of water, as marked, at full strength

Jack's: for water with 40 ppm or less of calcium and magnesium, such as RO.

Stage Length Jack's 5-12-26 Part A Jack's 15-0-0 Part B (calcium nitrate) Epsom salt Jack's 15-6-17 Clone Jack's 10-30-20 Bloom Jack's 7-15-30 Finish EC
Propagation (seedlings, clones, young plants) 3.15 g 1.1
Vegetative 3.79 g 2.52 g 0.99 g 2.4
Bud set (start of 12/12) 1 week 0.99 g 5.68 g 1.9
Flower 3.79 g 2.52 g 0.99 g 2.4
Late flower 1 week 0.99 g 5.41 g 2.1
Flush (clear water) 4 to 7 days
03

Notes from the chart

  • Amounts are grams per US gallon, from Jack's one-gallon schedule. Rates assume constant liquid feed and may need adjusting for your water and feeding frequency (Jack's).
  • EC targets are Jack's, for the full-strength mix.
  • Dissolve each powder fully in the full volume of water before adding the next. Calcium nitrate (Part B) and the phosphate and sulfate in Part A and Epsom salt form solids if combined as concentrates.

Source: Jack's Nutrients Nutrition Schedule: Jack's 3-2-1 One Gallon (cannabis and hemp, pure water sources)

04

What growers here actually run

From the THCFarmer archive

  • Runs Jack's 5-12-26, calcium nitrate and Epsom salt at 3, 2 and 1 grams per gallon, about 80 percent of Jack's full rate. Adjusts Epsom between 0.5 and 1 g depending on lighting, since Part A already carries magnesium.

    jguit Read the post →

  • Four years on Jack's in soil, coco and DWC. After trying additives, runs Jack's alone and feeds by meter, with about 60 percent of the PPM from Part A and 40 percent from Part B.

    HS90 Read the post →
05

Threads worth reading

Discussions this page draws on

06

Go deeper

Learn guides on THCFarmer

07

Common questions

What is Jack's 321?

Jack's 5-12-26 Part A, Jack's 15-0-0 Part B (calcium nitrate) and Epsom salt, in roughly a 3:2:1 ratio by weight. Jack's one-gallon chart uses 3.79 g, 2.52 g and 0.99 g. Members run about 80 percent of that, which is where 3-2-1 comes from, so the calculator starts at 80 percent (about 3 g, 2 g and 0.8 g per gallon).

What are the Clone, Bloom and Finish powders?

Jack's swaps in 15-6-17 Clone for propagation, 10-30-20 Bloom for one week at the flip (bud set) and 7-15-30 Finish for one week in late flower. Those weeks replace Part A and Part B. Many members run Part A, Part B and Epsom from start to finish instead.

My tap water is hard. Is this the right schedule?

This is Jack's pure-water schedule, for water with 40 ppm or less of calcium and magnesium, such as RO. For water with more calcium, Jack's points growers to its 15-5-20 and 18-8-23 schedules.

Still not sure? Ask the growers.

Post your nutrients, how much you're feeding, your medium and a photo. Members who've run Jack's 321 will tell you what they'd change.

08

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09

More grow tools

These numbers are starting points, not rules. Strains, water, medium and light all change what a plant wants, so watch your plants and adjust.

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