Petunias yellow? It may not be iron deficiency
If the symptoms appear as interveinal chlorosis (yellow leaves and green veins) of the new growth or if the symptoms progress to the point that the leaves turn completely yellow or white, this is often due to iron deficiency either from lack of iron application or high growing medium pH which makes iron unavailable for plant uptake.
A simple way to correct iron deficiency is to apply an iron chelate drench to the growing medium. This will not only provide more iron, but a good chelating agent will allow iron to be available over a higher pH range.
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