Chlorosis is yellowing of tissue that should be green, because the leaf is making or keeping too little chlorophyll. It is a symptom, not a diagnosis: nitrogen, magnesium, iron, manganese, sulfur and zinc shortages all cause it, and so do waterlogged or rotting roots, pH out of range, cold root zones and excess light (Marschner 2012).
In practice
Where the chlorosis starts is the first clue. On old, lower leaves it usually means a mobile nutrient (N, Mg, K) is being moved out to feed new growth; on new growth it points to an immobile one (Fe, Mn, Zn, S, Ca, B) or to high root-zone pH (Cockson et al. 2019). Uniform chlorosis of the whole leaf, veins included, differs from interveinal chlorosis, where the veins stay green. Chlorotic tissue can green up again if the cause is fixed early; once it turns brown it will not.
Don't confuse with
- Necrosis: dead, brown or black tissue, which follows severe chlorosis.
- Senescence: normal ageing and fade of old leaves, especially in late flower.
- Light bleaching: white or pale tops nearest the lamp, caused by light and heat rather than nutrition.
Overwatering is watering so often that the medium stays saturated, starving roots of oxygen, which causes drooping, slow growth and root disease.Decay of roots by pathogens such as Pythium, Fusarium, Rhizoctonia or Phytophthora, usually triggered by low oxygen, heat and waterlogging around the roots.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.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.A mobile nutrient is one the plant can move from older leaves to new growth, so its deficiency shows first on lower, older leaves: N, P, K, Mg, Cl, Mo.Yellowing of the leaf tissue between the veins while the veins themselves stay green; on old leaves it points to magnesium, on new leaves to iron or manganese.Death of plant tissue, seen as brown, tan or black patches, spots, tips or margins; it is permanent and the end point of many nutrient, salt, pest, disease and environmental problems.The programmed ageing and breakdown of leaves and other tissues, in which the plant recycles nutrients (especially nitrogen) from old leaves to developing flowers and seeds.The green pigment in chloroplasts that absorbs mainly blue and red light to drive photosynthesis; chlorophyll a and b are the main forms in plants.An immobile nutrient stays where it is first deposited, so its deficiency shows on young leaves and growing tips first: Ca, S, Fe, Mn, B, Cu.
