Hydranega – Aluminum Sulfate

Q: I think I poisoned my hydrangea bush. When I saw its pink blooms in May, I poured diluted aluminum sulfate directly onto the roots in order to change the acidity of the soil and get the flowers to turn blue. I did this for several evenings in a row before the leaves began to shrivel and turn brown. The hydrangea bush didn’t die completely and, since July, has sprouted somewhat deformed leaves. Next year will everything be back to normal, or should I give up and plant a new hydrangea?

A: Yikes! This is a classic example of “if a little is good, more must be better” thinking. In fact, aluminum is toxic to plants when present in large amounts. It’s most available when the soil pH is low. The sulfur in the aluminum sulfate lowers soil pH……so one application was OK but the next ones started you down a very slippery slope in terms of plant health. This is a case where you get to choose what you’d rather do: dig up the plant, remove the soil around it and plant a new one, or pour on some hydrated lime,1 cup per gallon in ONE application, to counteract the acidity and see what happens next year. Unless the hydrangea is a valued heirloom, I’d opt to remove it.

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