I am a master gardener and love, love, love helping people with their flowers...

Asked July 6, 2020, 10:06 PM EDT

I am a master gardener and love, love, love helping people with their flowers and gardens. With every one of their questions, I learn more. I have a friend in Watertown whose niece planted 3 hydrangeas 2 years ago with blue flowers. I don’t know the name of the cultivar. I was amazed when she told me that the shrubs are still blooming blue flowers. She says that there has been blue spruce trees next to two of the shrubs on the north that dropped their needles etc. in that area for many years and the one shrub on the south where a spruce had been removed and the shrub is now planted. Could that soil have become acidic enough to produce the acid for the flowers? Or, has a hydrangea been developed to produce blue flowers? Neither of my ideas seem likely to me but then I really don’t know. I’d really like an answer to my quandary. I’m excited to find the why of of the blue flowers. Will you help?

Clark County South Dakota

4 Responses

I wonder if we can get a photo of the site, as well as a photo of the trees in question. I'm not certain but I think most Hydrangea color is determined by soil acidity. This may be an issue with soil moisture or something related to how the blue spruce was planted, or a number of problems that blue spruce encounter in South Dakota.

You may also want to keep up with the "update" and read through past articles that touch on common problems that we experience across the state with our trees and climate, this would count towards MG education hours.

I’m sorry. I believe I did not make myself clear. I’m wondering why my friends hydrangeas have blue flowers. The soil in SD is not acidic enough to produce blue flowers yr after yr. on hydrangeas.

The reference to the blue spruce trees was to point out that for many years the tree has dropped its needles as it would normally onto the spot where the hydrangea is now planted. The other hydrangea is planted where a blue spruce once was and has now been taken out. It is my understanding, and I could be wrong, that spruce trees are an acidic plant.
My question was can, after many years of having acidic debris rest on an area, cause that area to become acidic enough to produce blue flowers on hydrangeas or change the soil composition to become more acidic than the general make up of the soil.

Sorry, I took that as the soil was being amended to get the hydrangea blue but if that is not the case, it is surprising that they would remain blue for so long as a majority of cultivars color is predetermined by the soil acidity. I've searched and haven't found anything other than what we already know (I cant find anything on a blue cultivar that won't just change back to pink when plopped in our soil). The needles from pines will make the soil acidic to some extent but that is temporary (and limited to just at the surface) as the needles break down, and after a few years the acidity returns to 'normal'. I'm also just a MG, and hydrangea aren't my thing, maybe Dr. Ball knows more

Thank u for your response. We r of the same mind when it comes to blue flowers. I’m glad to know that the spruce needles could make the top soil acidic. I just couldn’t believe that the acid could change the soil and on both sides of the house at that. But then, I certainly don’t know much when it comes to the wide wonders of this earth.
I will continue to investigate. Maybe next year the flowers will be pink and the mystery will be solved.
Thank u for your help. Tika