# Per-element feeding tricks: what growers adjust, stage by stage

> Experienced growers change single elements by stage rather than just turning the whole feed up or down: tapering nitrogen in late flower, cutting the ammonium share after the flip, a little extra calcium through the stretch, small magnesium, boron and zinc bumps in flower, silicon in veg. Most of these tricks are grower practice with little or no controlled research behind them. Two popular ones are contradicted by research: extra phosphorus above about 30–60 mg/L and potassium 'ramps' above about 250 mg/L did not raise yield or cannabinoids in controlled cannabis trials. Sugars and molasses feed soil microbes only, not the plant, and do harm in hydro. The GenetixBay approach is to taper nitrogen and keep everything else fed, which needs single salts or per-element dosing.

- Canonical: https://genetixbay.com/knowledge/nutrients/per-element-tricks.html
- Category: Nutrients · Level: Advanced
- Evidence: Grower practice · Status: Draft: awaiting expert review
- Stage: Veg, Transition, Flower, Ripening · Systems: Coco, Rockwool, DWC, RDWC, NFT, Ebb and flow, Drip, Aeroponics
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**What nutrient tricks do growers use in late flower?** In late flower, experienced cannabis growers change single elements rather than the whole feed: tapering nitrogen towards zero over the last 3-4 weeks, swapping calcium nitrate for an N-free calcium source, a small magnesium bump to about 65-75 mg/L, and slight boron and zinc increases. Most of these are grower practice with little controlled testing; the GenetixBay rule is taper nitrogen, keep everything else fed.

**Should I raise potassium in late flower?** Raising potassium in late flower is not supported by research: a controlled deep-water cannabis trial found no yield response anywhere between 60 and 340 mg/L potassium. Pushing potassium above about 300 mg/L commonly induces magnesium deficiency and calcium problems through cation competition. Keep potassium near 200-270 mg/L, with calcium at or above potassium in charge terms.

**Does more phosphorus in flower make bigger buds?** More phosphorus in flower does not make bigger cannabis buds once the feed supplies about 30-60 mg/L; that claim is a myth. Four independent controlled trials agree: in one, 30 mg/L already gave about 80% of maximum yield, and in another, 25, 50 and 75 mg/L gave the same yield while leachate phosphorus rose. Hold 40-60 mg/L.

**How much ammonium should be in a flowering feed?** A flowering cannabis feed should keep ammonium at or below about 10% of total nitrogen, dropping towards 0-5% in late flower, after 10-20% in veg. In a controlled trial cannabinoids were highest under pure nitrate. Cutting ammonium makes root-zone pH drift up faster, so plan more pH-down and use sulfuric or phosphoric acid rather than nitric.

**Should I add extra calcium during the stretch?** Adding extra calcium during the stretch, raising it from about 150 to 170-190 mg/L in flower weeks 1-3, is grower practice with no cannabis dose-response study behind it. The mechanism is sound, since fast growth builds a lot of new cell wall, but most stretch-time calcium deficiency is a delivery problem. Fix VPD and roots first.

**Does sulfur increase terpenes or skunky smell?** Extra sulfur does not increase terpenes; terpenes are hydrocarbons containing no sulfur, so that claim is a myth as a mechanism. The skunky note does come from [volatile sulfur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md), chiefly [3-methyl-2-butene-1-thiol](https://genetixbay.com/knowledge/glossary/prenylthiol.md), but no one has shown that feeding more sulfate raises them. Raising sulfur to 150-200 mg/L is untested grower practice.

**Should I keep silica in flower?** Whether to keep silica in cannabis flower is unresolved: stopping it around flower week 3-5 and running it to harvest are both grower practice with no evidence behind either. Growers commonly use 20-50 mg/L silicon from [potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md) in veg and early flower. If you stop it, remember potassium silicate also supplied some potassium.

**Does molasses make buds sweeter?** No, molasses does not make cannabis buds sweeter or fatter; that is a myth. Molasses and sugars feed soil microbes only, because plants make their own sugars by photosynthesis and do not take up meaningful sucrose through the roots. Taste comes from terpenes, plant health, drying and curing. In hydro, sugars feed biofilm, strip dissolved oxygen and raise root rot risk.

**Should I put plants in [darkness before harvest](https://genetixbay.com/knowledge/glossary/darkness-before-harvest.md)?** No, putting cannabis in 24-72 hours of darkness before harvest is a myth, and the GenetixBay founder calls it complete and utter nonsense. It cuts photosynthesis in the final, most critical days while the plant is still finishing resin. The founder has offered seeds for 20+ years to anyone who finds an unbiased peer-reviewed study showing a benefit; nobody has claimed it.

**Do cold nights increase terpenes?** Cold nights do not increase terpenes, flavour or resin; those claims are a myth until peer-reviewed data shows otherwise. Night temperatures of about 15-18 C (59-64 F) in the last 1-2 weeks do bring out real anthocyanin colour, but only in cultivars that carry it. Going too cold slows ripening.

**Should I drop EC before harvest or just cut nitrogen?** Cut only nitrogen before harvest rather than dropping the whole EC. A 20-40% whole-feed cut in the last 1-2 weeks lowers nitrogen but also starves potassium, calcium, magnesium, sulfur and micros while flowers are still adding weight and resin. The GenetixBay position is an element-specific taper. The one valid reason to lower input EC late is a salty root zone.

**How do I taper nitrogen without dropping calcium?** To taper nitrogen without dropping calcium, replace calcium nitrate with an N-free source. Gypsum at 0.6 g/L supplies about 140 mg/L calcium and 110 mg/L sulfur but must dissolve directly in the final solution, not a concentrate. Small doses of calcium chloride can fine-tune, keeping chloride below about 50-70 mg/L. Hold calcium at 130-180 mg/L.

**Short answer.** Good growers don't just turn the whole feed up or down. They move single elements: nitrogen tapered towards zero in the last 3–4 weeks, less ammonium after the flip, a little extra calcium through the stretch, small magnesium, boron and zinc bumps in flower, silicon in veg. Most of these are *Grower practice*: sensible, widely used, and barely tested. Two popular tricks are flatly contradicted by controlled cannabis trials: **more phosphorus** above about 30–60 mg/L and **potassium ramps** above about 250 mg/L did not raise yield or cannabinoids [3][4][5][6]. Sugars and molasses do nothing useful in mineral hydro. GenetixBay's own rule is simple: **taper nitrogen, don't flush, keep everything else fed**. A bottled 2-part can't do that; single salts or per-element dosing (what Jardin is built for) can.

<!-- FOUNDER NOTES: founder to add his own element tricks and ramp numbers here (then remove this comment) -->

## How to read this article

Every trick below is a **change from a base feed**, not a recipe on its own. The base is the flower recipe in [building a feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md): roughly N 150, P 50, K 250, Ca 150, Mg 55, S 115, Fe 2.5, Mn 0.5, Zn 0.3, B 0.4, Cu 0.08, Mo 0.04 mg/L at about 1.8–2.0 mS/cm. All amounts are mg/L (ppm by mass of the element) in the solution going to the roots. Salt percentages are in [hydroponic salts explained](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md); 1 g/L of a salt gives (percent × 10) mg/L of each element.

Two rules before you touch anything:

1. **Change one thing at a time** and write it down. If you move N, K and Mg in the same week, you'll never know which one did what.
2. **Every cation you add competes with the others.** Raising K pushes down Ca and Mg uptake; raising Mg or Ca pushes down K; ammonium pushes down all three. See [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md).

## The tricks at a glance

| Trick | Stage | Change from base | Evidence |
|---|---|---|---|
| N taper | Last 3–4 weeks | N stepped down to ~25 % then 0–20 mg/L; everything else unchanged | *Grower practice* (house approach); N/potency trade-off *Supported* [1] |
| Lower ammonium share | Flip onwards | NH₄ 10–20 % of N in veg → ≤10 % in flower | *Supported* [2] |
| "More P in flower" / PK weeks | Mid flower | P raised to 80–150+ mg/L | *Myth* beyond ~30–60 mg/L [3][4][5][6] |
| K ramp | Mid–late flower | K 250 → 300–400 mg/L | *Contested*: no yield response 60–340 mg/L [6] |
| Extra Ca in the stretch | Flower wk 1–3 | Ca 150 → 170–190 mg/L | *Grower practice* |
| N-free Ca source late | Taper weeks | Swap calcium nitrate for gypsum / a little CaCl₂ | *Established* chemistry; needed for the taper |
| Late Mg bump | Flower wk 5–end | Mg 55 → 65–75 mg/L | *Grower practice*; Mg–cannabinoid link *Supported* (one lab) |
| Extra S for aroma | Mid–late flower | S 115 → 150–200 mg/L | *Grower practice*, untested; "S for terpenes" *Myth* as a mechanism |
| Si in veg, stop in flower | Veg → mid flower | 20–50 mg/L Si, then 0 | *Grower practice*; stopping or keeping both untested |
| Fe chelate by pH | Any | EDTA / DTPA / EDDHA by root-zone pH | *Established* |
| B and Zn bump | Flower | B 0.4 → 0.5–0.6; Zn 0.3 → 0.4–0.5 | *Grower practice* |
| Mn, Mo, Cu | Any | Don't push | Caution: narrow windows |
| Cl, Na | Any | Keep low (Cl < 50–70, Na < 50) | *Supported* |
| Crop-steering EC ramp | Flip, late flower | Input EC up 0.4–0.8 mS/cm for generative steer | *Grower practice* |
| Late-flower EC drop | Last 1–2 weeks | Whole feed −20–40 % | *Grower practice*; inferior to an N-only taper |
| Molasses / sugars | Flower | 1–5 mL/L | Feeds soil microbes only, not the plant; *Myth* for the plant, harmful in hydro |
| Amino acids, fulvic/humic | Any | Label rate | *Contested* |
| Cold nights, darkness, drought | Last 1–2 weeks | Non-nutrient | Cold: colour real, terpene/resin gain *Myth*; darkness *Myth*; mild drought *Supported*, house-endorsed |

## Nitrogen

### 1. The late-flower N taper

**What and when.** From about 4 weeks before harvest, step N down: ~75 % of late-flower N at week −3, ~50 % at −2, ~25 % at −1, 0–20 mg/L in the final days. P, K, Ca, Mg, S and micros stay at normal late-flower strength.

**Claimed benefit and mechanism.** Lower N late in flower shifts the plant from building leaf and protein towards secondary metabolism and senescence of the fan leaves. In a controlled cannabis trial, higher N suppressed cannabinoid and terpenoid concentrations while inflorescence yield rose with N up to about 160 mg/L [1]. So less N trades a little bulk for a little potency percentage. The taper puts that trade to deliberate use at the stage when the plant has finished building its canopy.

**Evidence.** The N/potency trade-off: *Supported* (one controlled trial [1]). The taper ramp itself: *Grower practice*, widely recommended by experienced growers, not tested as a ramp. It is the **GenetixBay house approach**, and the reason Jardin doses per element.

**Risks.** Start too early (more than ~4 weeks out) and you cut yield, because the plant still needs N to fill flowers. Fan leaves will yellow from the bottom; that's expected. Purple stems and leaves at this stage are mostly genetics and cold, not a sign to stop.

**With single salts.** Drop calcium nitrate and [potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md) step by step. Take K from [potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md) and MKP, and Ca from an N-free source (trick 6). Full table and reasoning: [nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md). Why not to flush instead: [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). Pre-harvest flushing is a *Myth*, and a harmful one: it starves the plant while it is packing on its final weight and resin.

### 2. N form: the ammonium share

**What and when.** Run 10–20 % of total N as ammonium (NH₄⁺) in veg, then cut to ≤10 % from the flip and towards 0–5 % in late flower.

**Claimed benefit and mechanism.** Two things. **pH:** nitrate uptake makes roots release hydroxide and bicarbonate, so the root zone pH climbs; ammonium uptake releases protons and pulls pH down. A small ammonium share balances the two and holds pH steady in hydro without constant acid [10]. **Quality:** in a controlled cannabis trial (200 mg/L N, 0–100 % NH₄), cannabinoids were highest under pure nitrate; 10–30 % NH₄ was tolerated, 50 % cut yield by 46 % and showed toxicity, 100 % killed the plants [2].

**Evidence.** *Supported* (one rigorous cannabis trial [2], consistent with greenhouse practice [10]). The veg 10–20 % / flower ≤10 % split is *Grower practice* built on that.

**Risks and antagonisms.** Ammonium competes with K⁺, Ca²⁺ and Mg²⁺ for uptake. Too much gives Ca/Mg/K-shortage symptoms on a well-fed plant and a sliding pH. Cutting ammonium in flower means **pH will drift up faster**; plan for more pH-down, which itself adds N (nitric acid), P (phosphoric) or S (sulfuric). Count it.

**With single salts.** Greenhouse calcium nitrate already supplies about 7 % of its N as ammonium. To add more in veg, use small amounts of MAP or [ammonium nitrate](https://genetixbay.com/knowledge/glossary/ammonium-nitrate.md). In flower, use only calcium nitrate and potassium nitrate, and use sulfuric or phosphoric acid for pH-down during the taper so you're not sneaking N back in.

## Phosphorus

### 3. "More P in flower" and bloom boosters

**What growers do.** Raise P from about 50 to 80–150 mg/L or more in mid flower, often as a "PK week" with a concentrated booster.

**Claimed benefit.** Bigger, denser flowers, because P is in ATP and "flowering needs phosphorus".

**What the research says.** It doesn't work above moderate P. Four independent controlled trials agree:
- Shiponi and Bernstein tested 5–90 mg/L P in two cultivars: 30 mg/L gave about 80 % of maximum yield, flower P stopped rising above 30 mg/L, and cannabinoid concentration was highest below 30 mg/L, falling as yield rose (largely a dilution effect) [3].
- Westmoreland and Bugbee tested 25, 50 and 75 mg/L P: no significant effect on flower yield or cannabinoid concentration, but significantly more P in the leachate. Leaves took up 35 % more P and flowers 11 % more, with nothing to show for it [4].
- Hershkowitz et al. found the same again, and that raising overall nutrient concentration did not raise yield or cannabinoids either [5].
- Bevan et al. predicted a flower optimum near 59 mg/L P in [deep-water culture](https://genetixbay.com/knowledge/glossary/dwc.md) [6].

**Evidence.** "More P = bigger buds" beyond ~30–60 mg/L: *Myth*. The yield plateau: *Established* (four trials). See ["bloom boosters": what's real](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) and [phosphorus](https://genetixbay.com/knowledge/nutrients/phosphorus.md).

**Risks and antagonisms.** More runoff P (an environmental cost and money down the drain), and higher salinity. High P inducing **Zn and Fe deficiency** is well known in other crops [10]; in cannabis it is *possible but not shown*: the Shiponi and Bernstein ionome data didn't show a clear fall in flower Zn or Fe at 90 mg/L P [3]. Calcium phosphate also precipitates in concentrates and in high-pH solution. See [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md).

**With single salts.** Don't add P. If you want a flower P setting, hold 40–60 mg/L from MKP. During the N taper, MKP and phosphoric acid are your N-free P sources, so the taper doesn't touch P.

## Potassium

### 4. The K ramp and the K:Ca:Mg balance

**What growers do.** Raise K from about 250 to 300–400 mg/L from mid flower (weeks 4–8), usually with potassium sulfate or a [PK booster](https://genetixbay.com/knowledge/glossary/bloom-booster.md).

**Claimed benefit and mechanism.** K drives sugar transport into flowers, stomatal control and water relations, so more K should mean denser, heavier buds.

**What the research says.** In a flowering deep-water trial, yield showed **no response to K anywhere between 60 and 340 mg/L** [6]. One trial, one cultivar, but it's the only dose-response data in flower, and it doesn't support the ramp.

**Evidence.** K ramp for yield: *Contested* (strong grower lore; the one controlled trial found nothing [6]). K–Ca–Mg competition: *Established* in plant nutrition [10].

**Risks and antagonisms.** This is the real danger of the trick. K, Ca and Mg compete for uptake; pushing K above ~300 mg/L is a common cause of **induced Mg deficiency** (interveinal yellowing on older leaves) and Ca problems in late flower. Keep the cations balanced. A workable rule for soilless flower feeds, in meq/L: **K about 5–7, Ca about 7–9, Mg about 3.5–5**, i.e. Ca at or above K in charge terms. By mass, that is roughly K 200–270, Ca 140–180, Mg 45–60 mg/L. If you raise K, raise Mg a little with it (trick 7). See [potassium](https://genetixbay.com/knowledge/nutrients/potassium.md) and [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md).

**With single salts.** If you want a modest K lift, add potassium sulfate: 0.11 g/L adds about 50 mg/L K and 20 mg/L S. During the N taper, K comes from potassium sulfate and MKP instead of potassium nitrate, which keeps K steady while N falls.

## Calcium

### 5. Extra Ca through the stretch and early flower

**What and when.** Raise Ca from 150 to 170–190 mg/L in flower weeks 1–3, when the plant can double in height.

**Claimed benefit and mechanism.** Ca builds cell walls and membranes, and fast stretch growth means a lot of new wall. Ca moves only in the transpiration stream and can't be moved from old leaves, so growers front-load it.

**Evidence.** *Grower practice*. No cannabis Ca dose-response study exists. The mechanism is sound; whether the extra 20–40 mg/L matters is untested. Most stretch-time "Ca deficiency" is a **delivery** problem (low transpiration from high RH, cold or damaged roots, too much K, Mg or NH₄), not an empty tank. Fix VPD and roots first. See [calcium](https://genetixbay.com/knowledge/nutrients/calcium.md).

**Risks.** More calcium nitrate also means more N at a time when the stretch is already leafy. Ca competes with Mg and K. The idea that LEDs create a need for extra Cal-Mag is a *Myth* (house position); demand is cultivar-, water- and medium-driven ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)).

**With single salts.** 0.1 g/L calcium nitrate adds about 19 mg/L Ca and 16 mg/L N. If you don't want the N, use gypsum (below).

### 6. Switching to an N-free Ca source late

**What and when.** During the N taper, replace calcium nitrate with an N-free calcium source so Ca stays at 130–180 mg/L while N falls.

**Why.** Calcium nitrate is the main Ca source in nearly every feed. Cut it to cut N and you cut Ca too, in the weeks when the flowers are still building tissue. Without this switch, a taper turns into a Ca starvation.

**Evidence.** The chemistry is *Established*; the need follows directly from the taper.

**Options and limits.**
- **Calcium sulfate (gypsum, CaSO₄·2H₂O, ≈23 % Ca, ≈18.6 % S).** 0.6 g/L gives about 140 mg/L Ca and 110 mg/L S. It dissolves only to about 2 g/L and slowly, so it can't go in a concentrate. Dissolve it straight into the final solution or dose it from a stirred slurry. It roughly doubles S; with Epsom and potassium sulfate also present, total S can pass 250 mg/L. That's tolerated by most crops but raises EC, so trim potassium sulfate if needed.
- **Calcium chloride (CaCl₂·2H₂O, 27 % Ca, 48 % Cl).** Small doses only. 50 mg/L Cl brings just ~28 mg/L Ca, so use it to top up, not as the main source. Keep total Cl below ~50–70 mg/L ([chloride](https://genetixbay.com/knowledge/nutrients/chlorine.md)).
- A blend works best: gypsum for the bulk, a little CaCl₂ to fine-tune.

## Magnesium

### 7. The late-flower Mg bump

**What and when.** Raise Mg from about 55 to 65–75 mg/L from flower week 5 to harvest.

**Claimed benefit and mechanism.** Mg is the centre of chlorophyll and activates the enzymes that fix carbon. Growers claim it keeps upper fans green longer, supports resin, and prevents the late-flower Mg fade. Magnesium supply did change cannabinoid and terpene production in Bernstein's lab (see [magnesium](https://genetixbay.com/knowledge/nutrients/magnesium.md)); the veg optimum is 35–70 mg/L [7].

**Evidence.** *Grower practice*. The bump itself hasn't been tested in flower. The claim that it "raises THC" isn't shown; the claim that it prevents a late-flower Mg shortage is plausible, especially if K is high. Much late-flower Mg yellowing is induced by too much K or Ca, or low pH, not by too little Mg in the tank.

**Risks.** Mg competes with Ca and K. Above ~80–100 mg/L, Ca uptake suffers. Don't stack a Mg bump on a K ramp on a Ca bump: that's three cations all pushing up EC and each other.

**With single salts.** Epsom salt (magnesium sulfate heptahydrate): 0.1 g/L adds about 10 mg/L Mg and 13 mg/L S. Avoid [magnesium nitrate](https://genetixbay.com/knowledge/glossary/magnesium-nitrate.md) during the taper: it adds N.

## Sulfur

### 8. Extra S for aroma (terpenes and thiols)

**What growers do.** Raise S from about 115 to 150–200 mg/L in mid and late flower, for a louder nose.

**Claimed benefit and mechanism.** Two claims, and they need separating.
- **"S raises terpenes."** Terpenes are hydrocarbons; they contain no sulfur. S feeds them only indirectly (enzymes, general metabolism). Once S is sufficient, there's no mechanism for more S to make more terpenes. Calling this a sulfur trick is a *Myth* as a mechanism.
- **"S raises skunk."** This one has a real basis. The skunky note in cannabis comes from prenylated volatile sulfur compounds, chiefly 3-methyl-2-butene-1-thiol, which peak at maturity and in curing [8]. They do contain sulfur. But nobody has shown that feeding more sulfate raises them; they're present at tiny concentrations, so ordinary S supply is very unlikely to be limiting.

**Evidence.** *Grower practice*, untested. The compounds are *Established* [8]; the feeding link isn't. See [sulfur](https://genetixbay.com/knowledge/nutrients/sulfur.md).

**Risks.** Higher sulfate raises EC and can push Ca sulfate out of solution at high Ca. It does little harm at 150–200 mg/L, so it's a cheap experiment if you want to run one, side by side, same cultivar.

**With single salts.** Swap some potassium nitrate for potassium sulfate (more S, same K), or use Epsom salt. During the taper, S rises anyway as nitrates come out and sulfates go in.

## Silicon

### 9. Si in veg; stop or keep in flower

**What and when.** 20–50 mg/L Si from potassium silicate in veg and early flower for stiffer stems; many growers stop around flower week 3–5, others run it to harvest.

**Claimed benefit and mechanism.** Silicon is deposited in cell walls and is beneficial in many crops against abiotic stress and some fungal disease. Cannabis does take it up (see [silicon](https://genetixbay.com/knowledge/nutrients/silicon.md)).

**Evidence.** Si as a [beneficial element](https://genetixbay.com/knowledge/glossary/beneficial-element.md): *Established* in other crops. Yield, stem strength or quality benefits in cannabis: *Grower practice*, no direct cannabis trial found. Stopping in flower (claims about ash, trichomes or "hard" buds) and keeping it in flower are both *Grower practice*; neither has evidence behind it.

**Risks.** Potassium silicate is very alkaline and must go in first, into plain water, then pH-correct after everything else. It adds K, so count it against your K:Ca:Mg balance. It can precipitate with Ca in concentrates.

**With single salts.** Dose from a separate stock, first in the mix. If you stop it in flower, remember you've also removed some K.

## Micronutrients

### 10. Iron chelate choice versus pH

Choose the chelate for your root-zone pH, not for the price: **Fe-EDTA** holds iron to about pH 6.5, **Fe-DTPA** to about 7.5, **Fe-EDDHA** to about 9 [10]. In hydro and coco at pH 5.6–6.2, EDTA or DTPA is fine; DTPA gives headroom if pH drifts up (likelier once ammonium is cut in flower). In soil or with hard, alkaline water, use EDDHA. *Established*. No ramp is needed: hold 1.5–3.0 mg/L Fe. Too much iron competes with Mn. See [iron](https://genetixbay.com/knowledge/nutrients/iron.md).

### 11. Boron and zinc during flowering

**What.** Small bumps from mid flower: B 0.4 → 0.5–0.6 mg/L, Zn 0.3 → 0.4–0.5 mg/L.

**Claim.** B is needed for pollen tubes, cell walls and sugar transport; Zn for auxin and enzyme function. Growers bump them for flower set and density.

**Evidence.** *Grower practice*. There's no cannabis flowering dose-response data. Sinsemilla doesn't make pollen tubes, so the classic boron-for-seed-set argument doesn't apply to unpollinated flowers.

**Risks.** **Boron has the narrowest safe window of any nutrient**: toxicity starts around 5 mg/L in solution in cannabis work, and leaf-tip burn can show well below that in [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md) where B accumulates. Never "bump" boron without measuring what's already there. Zn rises are mild but compete with Fe and Cu. See [boron](https://genetixbay.com/knowledge/nutrients/boron.md) and [zinc](https://genetixbay.com/knowledge/nutrients/zinc.md).

**With single salts.** Boric acid (17.5 % B) and zinc sulfate heptahydrate (22.7 % Zn) from a 1:1000 micro stock: 0.6 g boric acid in 1 L of stock, dosed at 1 mL/L, adds about 0.1 mg/L B.

### 12. Manganese, molybdenum and copper: caution

Don't play with these. **Mn** competes with Fe (and excess Fe or Zn suppresses Mn); above about 1 mg/L in solution you risk Fe-like yellowing. **Mo** is needed in hundredths of a mg/L; there's no benefit to more. **Cu** is toxic to roots at low concentrations; stay within 0.03–0.1 mg/L, and watch copper pipes and copper-based "root" products, which add more than you think. Hold all three at the base-feed levels in [building a feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md).

### 13. Chloride and sodium: limits, not tricks

Keep **Cl below about 50–70 mg/L** and **Na below about 50 mg/L** in the feed, counting what your water brings. Both are salinity, not nutrition, at these levels. The one deliberate chloride use is small doses of calcium chloride during the N taper (trick 6). Sodium has no use; don't choose sodium-based pH-up or borate for a feed. See [chloride](https://genetixbay.com/knowledge/nutrients/chlorine.md) and [sodium](https://genetixbay.com/knowledge/nutrients/sodium.md).

## Whole-feed strength

### 14. Crop-steering EC ramps

**What.** In drain-to-waste coco and rockwool, growers raise input EC from about 1.8–2.4 mS/cm (vegetative steer) to 2.4–3.2 mS/cm (generative steer) at the flip to hold back the stretch and again in late flower, and let substrate EC climb on purpose with bigger drybacks.

**Mechanism and evidence.** Water and salt stress shift assimilates towards generative growth; *Supported* in greenhouse horticulture, *Grower practice* in cannabis for the specific numbers. One cannabis study found controlled late-flower drought raised THCA and CBDA concentration by about 12–13 %. Raising nutrient concentration overall did not raise yield or cannabinoids in recirculating hydro [5]. So EC is a steering lever (water and salt stress), not a way to feed more. Full method: [drain-to-waste and crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md).

**Risks.** Tip burn, stalled growth and midday wilting from over-steering; substrate EC more than ~1.5 mS/cm above input needs a flush shot (root-zone management, not a pre-harvest flush).

### 15. Late-flower EC drops versus element-specific changes

**What growers do.** Cut the whole feed by 20–40 % in the last 1–2 weeks (for example 2.0 → 1.3 mS/cm), as a softer version of a flush.

**What it actually does.** It lowers N, which is the part you wanted, but it also cuts K, Ca, Mg, S and micros in the weeks when the flowers are still adding weight and resin. It's a blunt version of the N taper, and it sits on the same slope as flushing: the further you cut, the closer you get to starving the plant.

**Evidence.** *Grower practice*. There's no controlled evidence for a benefit; long nutrient withdrawal costs dry mass and cannabinoid yield ([the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)).

**GenetixBay position.** Prefer the element-specific taper: **N down, everything else at normal late-flower strength**. Total EC will fall somewhat as nitrates come out; that's fine. The one legitimate reason for a lower input EC in late flower is a root zone that has run salty (high runoff or substrate EC); then lower the input to bring the root zone back into range, and fix the cause.

## Additives

### 16. Carbohydrates: molasses and sugars

**What growers do.** 1–5 mL/L molasses or other sugars in the last weeks, to "sweeten" or "fatten" buds.

**What's real.** Molasses and sugars feed soil microbes only, not the plant (house position). Plants make their own sugars by photosynthesis and don't take meaningful amounts of sucrose up through the roots to feed flowers. Taste comes from terpenes, plant health, drying and curing, not from sugar in the root zone. In living soil, molasses does feed microbes, which may speed nutrient cycling; molasses also carries some K, Ca, Mg and S.

**Evidence.** "Molasses sweetens or fattens buds" or feeds the plant: *Myth*. As a microbial food in living soil: *Grower practice*; that's the only thing it does.

**Risks.** In hydro and recirculating systems, sugars feed bacteria and biofilm, strip dissolved oxygen and raise the risk of root rot. Don't use them there. See [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md).

### 17. Amino acids, fulvic and humic acids

**What.** Amino-acid biostimulants, fulvic acid and humic acid at label rates, sold for uptake, stress tolerance and "chelation".

**What's real.** Humic and fulvic substances do complex metals and can improve micronutrient availability in soil. In the one cannabis study, humic acid supplementation didn't raise cannabinoids; it reduced the natural spatial variability of cannabinoids through the plant [9]. Amino-acid products have very little cannabis data.

**Evidence.** *Contested*. Plausible in soil and soilless with poor micronutrient availability; no consistent yield or quality benefit shown in cannabis mineral feeds.

**Risks.** **Amino acids are nitrogen.** A label-rate amino product can add 10–30 mg/L N without your noticing, which quietly undoes an N taper. Count them. Humics stain roots and reservoirs and can feed microbes in hydro.

## Non-nutrient finishing tricks

Briefly, because they aren't about elements:

- **Cold nights** in the last 1–2 weeks (for example 15–18 °C / 59–64 °F) bring out anthocyanin colour, but only in cultivars that carry it. The colour is real. Claims of more terpenes, flavour or resin from cold are a *Myth* until peer-reviewed data shows otherwise (house position). Too cold slows ripening. See [temperature by stage](https://genetixbay.com/knowledge/environment/temperature-by-stage.md).
- **A 24–72 h dark period before harvest** to "boost trichomes": *Myth* (house position). It cuts photosynthesis in the final, most critical days. See [trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md).

> **Greenleaf's standing challenge: darkness before harvest.** Putting plants in 24–72 h of darkness before the chop is a *Myth*, and the founder's verdict is "complete and utter nonsense": why cut photosynthesis in the most critical part of the life cycle, while the plant is still finishing its resin? For more than 20 years the founder has offered a standing challenge: find a peer-reviewed study showing a benefit (not a single-plant study, not biased or skewed) and a 50-pack of seeds is yours, no questions asked. Nobody has claimed it.

- **Mild late-flower drought**: one study found higher cannabinoid concentration; *Supported* (Caplan et al. 2019) and house-endorsed: the founder uses it, and some cultivars thrive when allowed to go a bit dry. Every cultivar responds differently, so test on one plant first ([crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md)).
- **Stem snapping (supercropping)**: *Grower practice*, house-endorsed; the founder does it all the time for better buds ([HST and supercropping](https://genetixbay.com/knowledge/training/hst-supercropping.md)).
- **UV-B**: little or no visible difference in controlled trials; see [light spectrum](https://genetixbay.com/knowledge/environment/light-spectrum.md).
- **Flushing**: *Myth*, and harmful ([the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)).

## A worked late-flower example (single salts, RO water)

Base flower feed from [feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) recipe 2, then the final week of the N taper with Ca held by gypsum. Per 1,000 L.

| Salt | Base (g) | Week −1 (g) | Week −1 supplies (mg/L) |
|---|---|---|---|
| Calcium nitrate | 790 | 200 | N 31, Ca 38 |
| Potassium nitrate | 200 | 0 | — |
| Gypsum (calcium sulfate dihydrate) | 0 | 500 | Ca 116, S 93 |
| MKP | 220 | 220 | P 50, K 63 |
| Magnesium sulfate heptahydrate | 560 | 600 | Mg 59, S 78 |
| Potassium sulfate | 240 | 420 | K 189, S 77 |
| **Totals** | **N 150, P 50, K 248, Ca 150, Mg 55, S 117** | | **N 31, P 50, K 252, Ca 154, Mg 59, S 248** |

Micros unchanged. Dissolve the gypsum directly in the tank and stir well; it won't go into a concentrate. pH-down with phosphoric or sulfuric acid, not nitric. Measure EC; the arithmetic is a guide.

## Common mistakes

- Running several tricks at once and crediting the wrong one.
- Ramping K and forgetting that it pushes Mg and Ca out.
- Stacking a PK booster on a complete base feed.
- "Tapering N" by diluting a 2-part, which cuts every element.
- Dropping calcium nitrate for the taper with no other Ca source.
- Adding amino acids or nitric acid during the taper and putting the N back in.
- Sugars in a recirculating system.
- Bumping boron without knowing what the water and the reservoir already hold.

## Evidence

- N/potency trade-off: *Supported* [1]. N taper ramp: *Grower practice* (GenetixBay house approach).
- Ammonium ≤10–30 % of N; cannabinoids highest on nitrate: *Supported* [2]. NH₄ pH effects: *Established* [10].
- No yield or cannabinoid gain above ~30–60 mg/L P: *Established* (four trials [3][4][5][6]). "More P in flower": *Myth*. High P inducing Zn/Fe shortage: *Established* in other crops [10], not demonstrated in cannabis [3].
- K ramp for yield: *Contested*; no response 60–340 mg/L K in one flower trial [6]. K–Ca–Mg competition: *Established* [10].
- Extra Ca in stretch, late Mg bump, B/Zn bumps, Si on/off: *Grower practice*. Mg veg optimum 35–70 mg/L: *Supported* [7].
- Volatile sulfur compounds behind skunk aroma: *Established* [8]; S feeding raising them: untested. "S raises terpenes": *Myth* as a mechanism.
- Chelate pH limits: *Established* [10].
- Higher overall concentration not raising yield or cannabinoids: *Supported* [5]. Crop-steering EC numbers: *Grower practice*.
- Pre-harvest darkness: *Myth* (house position). Cold nights: colour real, terpene/resin gain *Myth*. Mild late drought: *Supported*, house-endorsed; cultivars vary. Supercropping: *Grower practice*, house-endorsed. UV-B: little or no visible difference.
- Molasses feeding the plant: *Myth*; it feeds soil microbes only. Molasses in hydro: harmful. Humic acid: *Contested* [9]. Amino acids: *Contested*, little data.

## Sources

1. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516
2. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224
3. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323
4. Westmoreland FM, Bugbee B. 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652
5. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985
6. Bevan L, Jones M, Zheng Y. 2021. Optimisation of nitrogen, phosphorus, and potassium for soilless production of Cannabis sativa in the flowering stage using response surface analysis. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103
7. Morad D, Bernstein N. 2023. Response of medical cannabis to magnesium (Mg) supply at the vegetative growth phase. Plants 12(14):2676. https://doi.org/10.3390/plants12142676
8. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47). https://doi.org/10.1021/acsomega.1c04196
9. Bernstein N, Gorelick J, Zerahia R, Koch S. 2019. Impact of N, P, K, and humic acid supplementation on the chemical profile of medical cannabis (Cannabis sativa L). Frontiers in Plant Science 10:736. https://doi.org/10.3389/fpls.2019.00736
10. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6