A differential diagnosis is the clinician's way of thinking applied to plants: list all the causes that fit the symptom, then eliminate them in order of likelihood and cost of checking. Plant nutrition texts stress that visual symptoms alone are often ambiguous and need confirmation by analysis or by the plant's response to correction (Marschner 2012).
In practice
GenetixBay's order is: where on the plant it started, the pattern, then root zone and watering, pH, EC, climate, light, pests and disease, and only then a nutrient. The diagnosis graph behind the symptom checker scores each cause this way and asks the question that best separates the leading candidates.
Don't confuse with
- A guess from one photo: one answer with no ruled-out alternatives.
- A tissue test: one of the tests used within a differential, not the method itself.
The root zone is the volume of medium or solution where a plant's roots live, including its water, air, temperature, pH, EC and microbes.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.The daily length of light versus dark; photoperiod cannabis flowers when nights grow long enough, rather than at a fixed age.A tissue test is a lab analysis of dried leaf samples that measures the actual nutrient content of the plant, the most reliable way to confirm a deficiency or toxicity.Yellowing of normally green plant tissue caused by too little chlorophyll, from nutrient shortage, poor root uptake, pH lockout, light damage, pests or normal ageing.Systematic, regular inspection of plants, traps and roots to detect pests and disease early, identify them correctly and record numbers for decisions.A grow journal is a dated record of a grow, with photos, environment, feeding, problems and results, used to learn, share and prove what happened.Runoff EC is the conductivity of solution draining from the pot; compared with input EC, it shows whether salts are building up or being used up in the root zone.
