Something most rosarians seem not to recognize is symptoms of boron toxicity. It looks almost exactly like magnesium deficiency -- an inverted "V" or "Christmas tree" of green, on an otherwise yellow leaf, always on the oldest leaves of the plant. But I know my gardens are rich in Mg. This symptom turns up when the soil pH is too low, and too much boron becomes available. Sure enough, when measured, the pH under these symptomatic roses was around 4.9. The solution is to bring the pH up with some lime.
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