Short answer. Say where it started (old lower leaves, new top growth, the whole plant), what it looks like (between veins, edges, tips, spots, curling, coating), how fast it is spreading, and give the readings: pH and EC going in and coming out, temperature, RH, light intensity or distance, medium, system, water source, stage with days since the flip, and anything you changed in the last week. Add three photos in white light: the whole plant, the top of an affected leaf, and its underside.
"My plant is yellow, help" can mean twenty different things. A good description narrows it to two or three in one reply, and often answers itself.
Why does the description matter so much?
A diagnosis is a process of elimination, and each detail you give removes causes from the list. Location alone splits nutrient problems in half: mobile nutrients (N, P, K, Mg) show on old leaves, immobile ones (Ca, Fe, Mn, Zn, B) on new growth [1][2]. Root-zone pH and EC rule pH lockout and salt build-up in or out. A lens check rules pests in or out. Without those facts, any helper, human or AI, is guessing from a picture, and many problems look identical in a picture (lookalikes).
Which leaves are affected: old or new growth?
State whether the problem started on the oldest, lowest leaves, the newest leaves at the tops, or everywhere at once. That is the single most useful sentence you can write.
- Old growth: the big fan leaves at the bottom and inside of the plant, the first ones that grew.
- New growth: the youngest leaves at the shoot tips and the top of the canopy.
- Middle: recently matured leaves, a few nodes down from the tip.
- Whole plant: everything at once, often a watering, root or climate problem rather than a nutrient.
- Top only, nearest the lamp: usually light or heat.
- One side only: a fan, a wall, a light hotspot, or one root section.
Also say whether it is one plant or several, and if several, whether they share a reservoir, a water source or a cultivar. A problem on one plant among many identical ones points to that plant (roots, a pest, HLVd); a problem on every plant points to the room or the feed.
What words should I use for the pattern?
Use the specific pattern words below rather than "sick" or "burnt". Each one maps to a different set of causes.
| Say this | It means | Points toward |
|---|---|---|
| Uniform yellow | The whole leaf fades evenly, veins too | N, S, overwatering, senescence |
| Interveinal yellowing | Yellow between the veins, veins stay green | Mg (old leaves), Fe or Mn (new leaves) |
| Margin yellowing or scorch | Edges and serrations yellow then brown | K, salts, Mn toxicity |
| Brown tips | Only the very tip of each leaflet is dry and brown | Salt build-up, nutrient burn |
| Spots | Distinct round or irregular patches; say size and colour | Ca, P, septoria, spray burn |
| Stippling | Hundreds of pin-prick pale dots | Spider mites, thrips |
| Clawing | Leaf tips hook down | High N, overwatering |
| Taco or canoe | Leaf folds up along the midrib | Heat, high VPD, light |
| Drooping or wilting | Leaves hang from the petiole; say whether firm or limp | Watering, roots |
| Twisted or glassy new growth | Deformed, shiny tips | Broad mites, Ca or B, heat |
| Coating | Powder, fuzz, web, sticky film; say if it wipes off | PM, mites, honeydew |
Add colour (pale, lemon yellow, white, rust, bronze, purple, black), texture (crispy, papery, soft, slimy) and speed ("appeared overnight", "climbing one node a week").
How do I take photos that help?
Take three photos in white or natural light: the whole plant, a close-up of the top of an affected leaf, and the underside of the same leaf. Purple and warm-white LEDs hide yellowing and fake purpling, so switch to a white work light, a phone torch or daylight.
- Whole plant, so the helper can see the gradient from top to bottom.
- Close-up, upper surface, in sharp focus, filling the frame.
- Close-up, underside. Mites, thrips, eggs and septoria fruiting bodies live here [6].
- Scale: a coin, ruler or fingertip in the close-ups.
- Roots if you are in hydro or the plant wilts in wet media: one photo of the root mass.
- The same leaf again in 2–3 days, from the same angle. Progression is often the deciding clue.
Avoid photos taken with a filter, heavy zoom, or under the grow light alone. If you have a phone lens clip or loupe, a 10–30× macro shot of the underside is worth more than ten wide shots.
Which readings should I include?
Include root-zone readings, not just what you put in. Input pH and EC tell you what you fed; runoff or reservoir readings tell you what the roots are actually sitting in, and they are often different [4].
| Reading | Give | Why it matters |
|---|---|---|
| pH in and out | Input pH and runoff (or reservoir) pH | pH lockout causes many apparent deficiencies |
| EC in and out | Both values, in mS/cm, or ppm with the scale (500 or 700) | A ppm figure without its scale is ambiguous by 40% [5]; runoff far above input means salt build-up |
| Meter calibration | When you last calibrated | Uncalibrated meters cause false alarms |
| Air temperature | Lights-on and lights-off, at canopy height, in °C or °F | Heat, cold, VPD |
| RH | Lights-on and lights-off | VPD, mould risk, Ca delivery |
| VPD (if you track it) | kPa, leaf or air | Taco, slow growth, Ca spots |
| Light | PPFD at the tops (µmol/m²/s) if you have a meter; otherwise fixture wattage and distance | Bleaching, stretch; cannabis responds to light up to high PPFD when conditions allow [7] |
| Reservoir temperature (hydro) | °C or °F | Root rot and dissolved oxygen |
What setup details should I include?
Give the system, the medium, the water and the plant's age. The same symptom has different usual causes in soil and in DWC.
- Medium: soil (bagged or living), coco (buffered or not), rockwool, clay pebbles.
- System: hand-watered pots, drip to waste, DWC, RDWC, NFT, ebb and flow, aeroponics.
- Pot size and pot type (fabric or plastic).
- Water source: tap, well, RO, rain; any water report figures (alkalinity, sodium).
- Watering: how often, how much, to how much runoff; how heavy the pot feels now.
- Nutrients: type (mineral or organic, one-part or two-part) and strength; no brand needed, just the EC and any additives.
- Stage and age: seedling, veg, or flower; days from seed; and days since the flip (plus days since first pistils if you track it).
- Cultivar or seed source, and whether it is an autoflower.
- Recent changes in the last 7–10 days: new feed, water source, transplant, training, defoliation, light moved, heatwave, new clone, sprays.
What does a good problem report look like?
A good report fits in a dozen lines and answers every question a helper would ask. Compare these two.
Not enough to diagnose:
My plant has yellow leaves and brown spots. What's wrong? Using LED. Help!
Diagnosable:
Where: Lower and middle fan leaves on 2 of 4 plants; tops are fine. Looks like: Yellow between the veins, veins green, a few tan spots 2–3 mm. Started 5 days ago, now 3 nodes up. Underside: Checked with a 30× loupe, no insects or webbing. Stage: Flower day 32 from flip (day 20 of flower), photoperiod. Setup: Coco, 11 L fabric pots, drip to waste 3×/day to ~15% runoff. RO water. Feed: Mineral two-part plus Cal-Mag. Input EC 1.8 mS/cm, pH 5.8. Runoff EC 2.1, pH 5.3. Climate: 27 °C / 55% lights on, 21 °C / 60% lights off. PPFD ~900 at tops. Changes: Switched to the bloom part of the feed 7 days ago. Photos: whole plant, leaf top, leaf underside (white light).
That second report nearly diagnoses itself: interveinal yellowing on older leaves, low runoff pH and a recent feed change point to magnesium uptake suppressed by low root-zone pH, with a possible K-heavy bloom feed adding to it. The first report could be any of a dozen causes.
Copy-paste template
WHERE: (old/lower leaves, new/top growth, middle, whole plant, one side) — how many plants of how many
LOOKS LIKE: (pattern, colour, texture) — started (date), spreading how fast
UNDERSIDE (lens): (insects, eggs, webbing, black specks, nothing)
STAGE: (seedling / veg / flower) — days from seed: __ — days since flip: __ — auto or photo
CULTIVAR / SEED SOURCE:
MEDIUM + SYSTEM: — pot size: — watering how often, how much runoff:
WATER SOURCE: (tap / well / RO / rain) — water report if any:
FEED: (mineral/organic, strength) — input pH __ EC __ (scale: mS/cm / ppm500 / ppm700)
ROOT ZONE: runoff or reservoir pH __ EC __ — reservoir temp (hydro) __
METER LAST CALIBRATED:
CLIMATE: lights-on temp __ RH __ — lights-off temp __ RH __ — VPD __
LIGHT: PPFD at tops __ (or fixture watts and distance)
ROOTS (if checked): colour, smell, slime
CHANGES IN LAST 7–10 DAYS:
PHOTOS: whole plant / leaf top / leaf underside / roots — white light, with scale
How can a GenetixBay journal fill this in for me?
A GenetixBay journal already holds most of the template, so the symptom checker and the Professor can read it instead of asking you. Stage, days since flip, days of flower, medium, system, pot size, water source and cultivar come from your journal setup; logged pH, EC, temperature, RH and watering come from your entries (grow journal 101). The checker then only asks what it cannot know: where on the plant, the pattern, and what the lens shows.
When a Jardin controller is connected to the journal, its sensors log climate and reservoir readings continuously, so the conditions in the days before the symptom appeared are already on record. That history is often the deciding clue: the heat spike two nights ago, or the pH that drifted for three days. Jardin is in development; until then, manual journal entries do the same job.
What should I check before asking for help?
- Lens on the underside of three affected leaves.
- Lift the pot or check the reservoir temperature and air.
- Calibrate and read input and runoff pH and EC (meter calibration, runoff testing).
- Read climate at canopy height, lights on and off.
- Write down what changed. Then fill in the template.
Doing these five checks first often solves the problem before you post it (how to diagnose any problem).
Common mistakes
- Photos under the grow light only; colour is distorted.
- One close-up of one leaf, with no whole-plant view.
- "pH is fine" without a number, or input pH only.
- A ppm figure with no scale.
- Leaving out recent changes, especially a new feed, a flip or a transplant.
- Removing all the damaged leaves before asking; they are the evidence.
- Changing three things at once after asking, so nobody learns which fix worked.
Evidence
- The old-versus-new growth rule is Established plant nutrition [1] and holds in cannabis trials [2][3].
- Root-zone sampling by pour-through or runoff as the reading that matters is Established extension practice [4].
- The 40% difference between ppm scales is Established meter physics [5].
- The report template and photo rules are Grower practice, built for GenetixBay's symptom checker.
