General Hydroponics Feeding Schedule for Cannabis

What the GH feeding schedule is

General Hydroponics publishes a feeding chart for its Flora Series three-part liquid nutrients: FloraMicro (nitrogen, calcium, micronutrients), FloraGro (nitrogen, potassium for vegetative growth), and FloraBloom (phosphorus, potassium, magnesium, sulfur for flowering)^[1]. The chart lists milliliters per gallon of each bottle across stages — seedling, early veg, late veg, transition, early bloom, mid bloom, late bloom, ripen, and flush — plus optional supplements like CaliMagic, Rapid Start, Floralicious Plus, Liquid KoolBloom, and Diamond Nectar^[1][2].

The schedule exists in two main variants: the Recirculating version (for reservoir/DWC/RDWC systems) and the Drain-to-Waste version (for coco, soilless, or run-to-waste hydro), which uses slightly lower concentrations because nutrients aren't accumulating in a reservoir^[1]. GH also publishes an Aggressive vs Easy version — the aggressive chart pushes higher EC and is closer to what commercial growers use^[2].

Why growers use it

The Flora Series has been sold since the 1970s and is one of the most widely available hydroponic nutrient lines in North America^[3]. Three specific reasons it stays popular for cannabis:

• Adjustable ratios. Because it's three separate bottles, you can shift the N:P:K by changing the ratio of Gro:Micro:Bloom instead of switching products. This is genuinely useful compared to single-bottle "grow" and "bloom" formulas.
• Predictable and cheap. It's available at most hydro shops and Amazon, and a gallon set lasts a small grow through multiple cycles.
• Documented. The label and PDF chart give exact ppm/EC targets, which is easier for beginners than guessing^[1].

What it is not: a magic yield booster. Controlled comparisons of major nutrient brands are rare, and there's no credible peer-reviewed evidence that Flora Series produces higher cannabis yields than comparable lines like Canna, Athena, Jack's, or MegaCrop No data. The value is consistency, not superiority.

When to start

Seeds and fresh clones don't need synthetic nutrients. Cotyledons carry enough stored energy for the first 7–14 days, and rooted clones need root development before feeding heavily^[4].

Start light feeding when:

• Seedlings have 2–3 sets of true leaves and are actively growing.
• Clones show new leaf growth after transplant, indicating roots have taken hold.

Begin at roughly 25% of the GH chart's seedling column (about 0.6 EC / 400 ppm on the 500 scale) and work up over 1–2 weeks. The published seedling numbers are not unsafe, but many growers find them slightly hot for young plants under LED Anecdote.

How to mix and feed, step by step

The GH chart specifies the order of operations, and it matters — mixing FloraMicro and FloraBloom together while concentrated will precipitate calcium phosphate and lock out nutrients^[1][2].

Step-by-step for a 5-gallon reservoir, mid-veg (as an example):

1. Start with clean water. RO or filtered is ideal. If using tap, know your starting EC and calcium/magnesium content.
2. Add FloraMicro first. Per the chart, ~5 mL/gal in mid-veg. Stir.
3. Add FloraGro second. ~5 mL/gal. Stir.
4. Add FloraBloom third. ~5 mL/gal even in veg — the small amount of P and K helps root and stem development.
5. Add any supplements (CaliMagic if using RO, etc.) one at a time, stirring between.
6. Check EC/TDS. Mid-veg target is roughly 1.2–1.6 EC (600–800 ppm 500-scale) for most cannabis genetics^[1].
7. Adjust pH last. Target 5.5–6.2 for hydro/coco, 6.0–6.8 for soil^[5]. Use GH pH Down (phosphoric acid) or pH Up (potassium hydroxide/carbonate).
8. Feed. In DWC, top off the reservoir; in coco, water to ~10–20% runoff each feeding.

Stage-by-stage EC targets (rough, not gospel):

• Seedling / early veg: 0.6–1.0 EC
• Late veg: 1.2–1.6 EC
• Transition / stretch: 1.4–1.8 EC
• Peak flower: 1.6–2.2 EC
• Late flower / ripen: 1.2–1.6 EC
• Flush (optional): plain pH'd water

Run the 50–75% column of the chart if you're new, growing under 400W-equivalent lighting or less, or running autoflowers. The full chart assumes strong lighting and hungry photoperiod plants.

Common mistakes

• Running full chart strength on seedlings or weak lights. Burnt tips within a week. Cut to 25–50%.
• Mixing Micro and Bloom together in concentrate. Causes precipitation. Always add Micro first, into water, and stir before the next bottle^[1].
• Ignoring EC. The chart's mL/gal only produces the intended EC if your starting water is near-zero. Hard tap water can start at 0.4–0.8 EC before you add anything.
• Chasing every supplement. CaliMagic is genuinely useful with RO water. Floralicious Plus, Liquid KoolBloom, and Diamond Nectar have thin evidence for cannabis-specific benefit Weak / limited.
• Long flushes based on folklore. The claim that a 2-week flush improves smoke quality is popular but not supported by controlled research; one published trial found no sensory or chemical benefit from flushing^[6] Disputed. A 7–10 day taper is a reasonable middle ground.
• Not calibrating meters. pH and EC pens drift. Calibrate monthly with reference solution.

Related techniques and alternatives

• Jack's 321 — a dry salt program (Jack's 5-12-26, calcium nitrate, Epsom) that many commercial growers prefer for cost and simplicity.
• Coco coir feeding — coco specifically benefits from daily fertigation and Cal-Mag supplementation; the GH drain-to-waste chart applies.
• EC and PPM basics — understanding what you're measuring matters more than which bottle you pour.
• pH management — the single most common cause of "nutrient deficiency" symptoms is actually pH drift, not feed strength.
• Flushing before harvest — the evidence, the folklore, and the middle ground.

Sources

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