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Report From PIA – February 5

I got an email today from a woman who was perplexed about her hydrangeas. “They’ve been blue for several years,” she wrote, “but the last two years they got taller and turned pink.” She wondered if the height and color change were related.

Full disclosure here: the photos below are not from her garden. I took a photo of a blue hydrangea and tinted the flowers pink with Photoshop. Think illustration, not documentation.

I told her that I thought that she has Nikko Blue hydrangeas, and these grow to be well over five feet tall when mature. Additionally, all of these shrubs grew taller last summer because of the wet season. I doubt that the size is related to the color.

Blue hydrangeas stay blue when the plant is growing in acidic soil. It’s aluminum in the soil that turns them blue, but they can’t absorb that mineral unless the soil is on the acid side. In alkaline soils these hydrangeas will be pink.

Occasionally a hydrangea can turn pinkish in acidic soil if a lot of phosphorous has been applied to the area. Phosphorous can tie up the aluminum so that the plant can’t take it up, even though the pH is in the right range. So if you want your hydrangeas to stay blue, don’t use super phosphate around them.

In the Northeast most of us have acidic soil because of the native soil and acid rain. Usually if we do nothing our hydrangeas stay blue. Leaching from cement foundations can sweeten soil, however, and lime that’s applied to lawns can be spread into neighboring beds which raises the pH in that area.

I haven’t heard back from the flummoxed emailer yet, so I don’t know which of these situations might apply to her.

And here’s one way hydrangea color relates to our lives: we all need particular growing conditions in order to do well. I need to eat regularly, and stay away from very hot environments, for example. It’s good for me, and those around me, that I know that about myself, because I can be really cranky when hungry or hot.

What growing conditions cause you to turn from pink to blue?

A Nikko Blue hydrangea will always be either light blue or light pink. You can't make this one dark blue or deep purple. You can make a Nikko Blue pink - scatter lime around the shrub in the spring and fall, or use wood ashes in the same seasons.

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