Jack's 321 vs Flora Series

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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: 3.6 g Part A, 2.4 g Part B, and 1.2 g Epsom — commonly rounded to '3-2-1' ^[1]. It is a two-part dry salt program designed to provide complete nutrition from seedling through flower at one fixed ratio.

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 phases.

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 and cool.
• One ratio for the entire grow simplifies decision-making and reduces mixing errors.
• Predictable EC and ion balance because you're weighing pure salts.

Reasons to pick Flora Series:

• Liquid concentrates are faster to mix; no precise scale required.
• Stage-specific nutrient ratios are built into the product line and feed charts.
• Widely available in hydro shops worldwide.
• Pre-formulated to minimize precipitation when mixed in the recommended order.

Claims that one produces 'better terpenes,' 'more resin,' 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' (1.8 g / 1.2 g / 0.6 g 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 Disputed. One published cannabis study comparing 0, 7, 10, and 14 day flushes found no significant differences in cannabinoid content, terpene profiles, or sensory scores ^[2].

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 (below 100 ppm). Leave headroom for mixing.
2. Weigh 3.6 g of Part A (Jack's 5-12-26) on a 0.01 g precision scale. Add to water and stir until fully dissolved.
3. Weigh 2.4 g of Part B (calcium nitrate, 15.5-0-0). Add only after Part A is dissolved — never combine the dry salts directly, or you will precipitate calcium phosphate and sulfate, locking out both nutrients Strong evidence. Stir until completely clear.
4. Weigh 1.2 g of Epsom salt (magnesium sulfate heptahydrate). Add and stir thoroughly.
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 and coco; 6.2–6.5 for peat-based mixes.
7. Use within 5–7 days; mix fresh for recirculating systems weekly to avoid pH drift and microbial growth.

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 that omits FloraGro ^[3]):

1. Fill reservoir with your source water.
2. Add 8 mL of FloraMicro first. Shake the bottle before pouring. Micro contains the calcium; it will precipitate if it meets concentrated phosphate from FloraBloom undiluted Strong evidence.
3. Stir thoroughly.
4. Add 16 mL of FloraBloom. Stir again until fully mixed.
5. Check EC — typically around 1.6 mS/cm above source water.
6. Adjust pH to 5.8 (hydro and coco) or 6.2–6.5 (soilless mixes).

For the standard GH feed chart, use FloraGro, FloraMicro, and FloraBloom in stage-specific ratios (e.g., 2-1-1 early veg, 1-2-2 mid bloom). Follow the ratios on the bottle or chart and start at half the listed dose, then increase as plants establish.

Common mistakes

• Combining concentrates or salts directly. With both programs, mixing the calcium-containing part with the phosphate/sulfate part undiluted causes white precipitate — locked-out nutrients Strong evidence. Always add to water separately, in order, with stirring between additions.
• 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 underlying 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.' They are a sign of excess salts.
• 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 (below 50 ppm).
• Using a kitchen scale for Jack's. A ±1 g scale is useless when you are weighing 1.2 g of Epsom. A 0.01 g jeweler's scale costs $15 and prevents dosing errors.
• Believing the marketing. Neither program needs the optional 'boosters' sold alongside it — bloom boosters, sugar additives, enzyme products, and rooting stimulants are marketed heavily but lack convincing evidence of yield benefit Weak / limited.

Related techniques

• Jack's 321 Formula — detailed breakdown of the ratio and its history.
• General Hydroponics Flora Series — overview of the product line and feed charts.
• Nutrient Lockout — how precipitation and antagonism cause deficiency symptoms.
• pH Management in Cannabis Cultivation — why pH drifts and how to stabilize it.
• 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; see Coco Coir Growing.
• Living soil / no-till — replaces salt-based feeding with biology; not directly comparable to either program.

Sources

How this page was made

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