Jack's 321 vs Flora Series

What they are

Jack's 321 is a mixing ratio for JR Peters' Jack's Hydroponic 5-12-26 fertilizer, combined with calcium nitrate (15.5-0-0) and Epsom salt (magnesium sulfate). The numbers refer to grams per gallon: 3.6g Part A (5-12-26), 2.4g Part B (calcium nitrate), 1.2g Epsom — commonly rounded to '3-2-1' ^[1][2]. It is a two-part dry salt program designed to be a complete nutrient at one ratio from seedling through flower.

Flora Series is General Hydroponics' three-part liquid line: FloraMicro, FloraGro, and FloraBloom. The ratios change by growth stage — for example, the 'Lucas Formula' uses only FloraMicro and FloraBloom at an 8 mL : 16 mL per gallon ratio, while the standard GH feed chart adjusts all three parts across vegetative, transition, and bloom ^[3].

Both are general-purpose hydroponic nutrients suitable for DWC, coco, rockwool, and peat-based soilless mixes. Neither is designed for true living soil.

Why growers use one or the other

Reasons to pick Jack's 321:

• Cost per gallon of finished nutrient is significantly lower than premixed liquids Strong evidence — dry salts contain no water shipping weight.
• Shelf-stable for years when kept dry.
• One ratio for the entire grow simplifies decision-making.
• Predictable EC and ion balance because you're weighing pure salts.

Reasons to pick Flora Series:

• Liquid concentrates are faster to mix; no scale required.
• Adjusting N-P-K by stage is built into the product line.
• Widely available in hydro shops worldwide.
• More forgiving with hard tap water at moderate doses because the micro is buffered.

Claims that one produces 'better terpenes' or 'denser buds' than the other are folklore Anecdote. No controlled cannabis trial has shown a yield or quality difference between these two programs when both are run at appropriate EC and pH.

When to start

Start either program once seedlings have their first true serrated leaves and a small root system, or once clones show new growth after rooting. Begin at roughly half strength (around EC 0.8–1.0 above your source water) and ramp up as the plant grows.

• Jack's 321: Some growers run 'half 321' (1.8g / 1.2g / 0.6g per gallon) for the first 1–2 weeks, then move to full strength.
• Flora Series: Follow the 'seedling' or 'early veg' column on the GH feed chart, or run a half-strength Lucas Formula (4 mL Micro / 8 mL Bloom per gallon).

Stop or reduce nutrients in the final 1–2 weeks of flower only if you choose to flush. Whether flushing improves smoke quality is disputed — the one published cannabis study on flush duration found no significant difference in cannabinoids, terpenes, or sensory scores across 0, 7, 10, and 14 day flushes ^[4] Disputed.

How to mix Jack's 321 (step-by-step)

Per 1 US gallon (3.785 L) of finished nutrient solution:

1. Fill your reservoir with RO or low-EC tap water. Leave headroom for mixing.
2. Weigh 3.6 g Part A (Jack's 5-12-26) on a 0.01 g scale. Add to water and stir until fully dissolved.
3. Weigh 2.4 g Part B (calcium nitrate, 15.5-0-0). Add only after Part A is dissolved — never combine the dry salts directly, or you'll precipitate calcium phosphate/sulfate. Stir until clear.
4. Weigh 1.2 g Epsom salt (magnesium sulfate heptahydrate). Add and stir.
5. Check EC. Expect roughly 1.6–1.8 mS/cm above your source water at full strength.
6. Adjust pH to 5.8 for hydro/coco, 6.2–6.5 for peat mixes.
7. Use within 5–7 days; mix fresh for recirculating systems weekly.

Scale linearly for larger batches. For 5 gallons: 18 g / 12 g / 6 g.

How to mix Flora Series (step-by-step)

Per 1 US gallon, using the Lucas Formula (a simplified two-part schedule popularized on hydro forums ^[5]):

1. Fill reservoir with source water.
2. Add 8 mL FloraMicro first. Shake the bottle before pouring. Micro always goes in first — it contains the calcium, which will precipitate if it meets concentrated phosphate from Bloom.
3. Stir thoroughly.
4. Add 16 mL FloraBloom. Stir again.
5. Check EC — typically around 1.6 mS/cm above source water.
6. Adjust pH to 5.8 (hydro/coco) or 6.2–6.5 (soilless mixes).

For the standard GH chart, use FloraGro/Micro/Bloom in stage-specific ratios (e.g., 2-1-1 early veg, 1-2-2 mid bloom). Follow the chart on the bottle and start at half the listed dose.

Common mistakes

• Combining concentrates directly. With both programs, mixing the calcium-containing part with the phosphate/sulfate part undiluted causes white precipitate — locked-out nutrients. Always add to water separately, in order, with stirring between Strong evidence.
• Chasing pH up and down daily. A drifting pH usually means EC is wrong, roots are stressed, or your reservoir is too small. Fix the cause, not the symptom.
• Running too hot. Cannabis rarely needs EC above 2.0–2.4 mS/cm even in heavy flower. Burnt tips are not a sign of 'feeding well.'
• Ignoring source water. Tap water with 150+ ppm of calcium and magnesium changes the math. Jack's 321 in particular is calibrated assuming RO or very soft water.
• Using a kitchen scale for Jack's. A ±1 g scale is useless when you're weighing 1.2 g of Epsom. Spend $15 on a 0.01 g jeweler's scale.
• Believing the marketing. Neither program needs the dozen optional 'boosters' sold alongside it. Bloom boosters, sugar additives, and most enzyme products have weak or no evidence of yield benefit Weak / limited.

Related techniques

• MegaCrop and Masterblend 4-18-38 — other one-part or two-part dry salt programs in the same niche as Jack's.
• Coco-specific feeds (Canna Coco, House & Garden) — formulated for the cation exchange behavior of coir.
• Living soil / no-till — replaces salt-based feeding with biology; not directly comparable.
• EC and pH management — far more important than nutrient brand.
• Runoff EC monitoring in coco — tells you whether to feed harder or flush.

Sources

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