Answer: These plants are tolerant of a range of soil pH so I do not think it would be caused by pH unless your soil has somehow become extremely off balance. It is probably soil related however. Soil and nutrients are very complex. For example, if excessive aluminum sulfate was used to acidify the soil at some point, it could cause a toxicity problem -- interveinal chlorosis is actually a sign of that. Or, there are many micronutrients needed for plant health and perhaps one is deficient or the plant is unable to take it up for some reason -- I am thinking magnesium in this instance as a possibility especially if the soil has been over-acidified. There is also the possibility, if it is a new plant within the last few years, that it has not rooted out into the surrounding soil and instead is rootbound and growing in the original soil it came with. This could lead to problems even though your native soil is fine. I would suggest you work with your county extension to test your soil and possibly examine a representative leaf to try to determine what is causing the problem. Good luck with your hydrangea!
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