The Q&A Archives: Hydrangeas

Question: I have 3 hydrangea bushes, which I use lime to turn them blue - last year they were very pretty and stayed blue for a long time, this year I did the same thing but two of the bushes were blue for only a short time and then turned white and look as if they are dying - can you tell me what is causing this problem - thank you - and should I prune them back in the fall halfway or to the ground as they are kind of leggy?

Answer: The bigleaf hydrangeas (Hydrangea macrophylla) that change color in response to pH will be blue in an acid soil and pink in an alkaline soil. The lime you added would be making the soil less acid and more alkaline. Unfortunately, too much lime and/or too fast or too extreme a pH change would be detrimental to the plants.

At this point, I would strongly suggest you run some basic soil tests and do any adjustments only as indicated by the tests. I would also strongly suggest you work with your county extension or qualified nursery personnel as to how best to handle the pH at this point; they should also be able to help you with the tests and interpreting the results. Lime can be very slow acting and thus the results of your prior applications may take some time to work their way through the soil.

This type of hydrangea blooms from buds on wood that grew the previous year. For this reason, they can be trimmed if needed right after blooming. If you prune them in the fall, winter, spring or early summer you will be removing flowering wood. The primary pruning these plants would need is just an occasional light thinning, to remove some of the oldest stems by cutting them off at the base. In late spring any truly winter killed tips can also be removed, but be very patient to make sure the wood is truly dead before you remove it.

Good luck with your hydrangeas.

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