Yellow leaves don’t mean “add fertilizer.” They mean three different things depending on where the yellowing starts.
That’s true for almost every leaf symptom. The plant is telling you what’s wrong — but the diagnosis depends on which leaves, which part of the leaf, and whether it’s new or old growth.
The quick read:
– Lower leaves yellowing first — nitrogen. The plant pulls it from old leaves to feed new ones
– Upper leaves yellow with green veins — iron. New growth can’t get enough
– All leaves yellowing evenly — overwatering. The roots are suffocating
– Leaves turning purple — phosphorus
– Brown crispy edges — potassium
– Leaves curling inward — water stress
– Spots — fungal
– Holes — insect
The difference between nitrogen and iron is which end of the plant turns yellow first. Most of the time, the leaf already told you the answer before you opened the fertilizer bag.