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Hydrangeas Garden

Overdose aluminum sulfate

7 months ago

Hello!

I applied aluminum sulfate to my hydrangeas in hopes that they would bloom blue but I misread the instructiins and put way too much… about teo general handfuls around each plant that I then watered in. is there any way that I can help to mitigate the damage?? maybe flushing them with water might help??

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Comments (6)

gardengal48 (PNW Z8/9)
7 months ago
Was that two (2) handfuls of aluminum sulfate applied per plant? If so, that may not be too much. The recommendation is 1 cup of a 15% concentration of AS for a 4' hydrangea, although it is generally applied in a couple of applications rather than all at once. If you think you applied too heavily, flushing the plant well with water can help.

FWIW, I would have thought your soil pH in CT acidic enough to produce blue flowered macs without having to resort to AS. Not so?
Susan 7a, CT
Original Author
7 months ago
Hi there,

Thank you for your reply and insight! Yes, it was 2 handfuls per plant… and they are about 3’ tall. For all they say about new england being perfect for blue hydrangeas, that doesn’t seem to be the case with mine! I think perhaps it has to do with the cement foundation of the house as I end up with mostly pink and purples. I am a new gardener and have been so eager (and impatient) to get my hands in everything and so I made this mistake in a rush today. I will try flushing it well with water and hope for the best!!
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Naturally acidic soils are common here on much of the west coast and aluminum sulfate is readily available at any nursery as well as all the box stores and other places that carry plant fertilizers and amendments. I'd be cautious about using alum as a substitute - there are many formulations of alum and their chemical characteristics are not the same. Plus, it would be difficult to tell if you are applying enough or overapplying since it doesn't come with any directions for use in the garden. Agricultural sulfur is useful for acidifying soil but if you do not have aluminum present in sufficient levels, it will not help to turn hydrangeas blue - it the access to aluminum that makes hydrangeas blue.
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gardengal48 (PNW Z8/9)
7 months ago
Ah yes - proximity to concrete could cause problems with the bluing :-) But I honestly don't think you have done any damage. Unless you have very big hands, two handfuls is barely going to make a cup, so you should be good.
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Susan 7a, CT
Original Author
7 months ago
Thank you so much, I feel so relieved to hear this from you! I am hoping gardening will teach me how to be more patient and thoughtful going forward!! 🙃 Many thanks again!
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luis_pr
7 months ago
last modified: 7 months ago
I accidentally dropped too much when my dogs were playing with each other as I was about to drop a/s into the ground. I just picked it up and applied it elsewhere. And watered well. Just pick up the excess and apply it to another plant or add it back into the a/s bag. I did make a few soil tests after 2 or 4 weeks later with my soil pH kit just to ensure the pH was not off the charts. Not a terribly accurate unit but enough to calm me down. You can monitor the plants too to see if they react.
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Susan 7a, CT
Original Author
7 months ago
Thanks, Luis! I feel much better knowing all of this. I was so panicked yesterday. I tried scooping some sugar with my hands last night and it turns out that is only 1/8 cup 😂 Phew!

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