Climbing Hydrangeas. Changing their colour to blue. Climbing varieties


Hello, I live up near Yonge and Finch and I was hoping to plant a climbing hydrangea along a western fence in shade, but I was unable to find any information on whether it’s possible to alter the colour of a climbing hydrangeas blooms (preferably I’d like blue if possible). Do you know if this is possible? Additionally, is it possible to grow climbing hydrangeas that have flowers closer to the snowball hydrangea rather than the lacecap? I saw pictures online of some but I’m not sure if they were Photoshopped. Many thanks!! Diana


Hi Diana,

This question brought back sweet memories of my childhood, when I remember watching my Mother adding rusty nails to her hydrangea bed to turn the blooms blue. They were magnificent.

The colour of some hydrangeas is determined by the acidity or alkalinity of your soil.  The change actually occurs due to the availability of aluminum depending on the pH of the soil. Generally speaking, acidic soil, with a pH lower than 6.0, yields blue or lavender-blue hydrangea blooms. Alkaline soil, with a pH above 7.0, promotes pinks and reds. With a pH between 6 and 7 (neutral), the blooms turn purple or bluish-pink. This is true of coloured hydrangeas, not white ones.

There are a number of ways to lower your soil pH. The most common way is to add garden sulfur or diluted aluminum sulfate. Many internet articles, such as this one from  Landscape Ontario, also claim that you can modify soil pH by adding coffee grounds, chopped up citrus peel, finely crushed eggshells or pine-tree needles, digging these additives/amendments into the soil, adding only a small amount at a time, but doing it regularly.

If you wish to learn more about the scientific cause for the change, and get a longer list of what you could add to your soil to change its pH, here is the link to an interesting article: American Scientist

Now to your second question on varieties of climbing hydrangeas and whether a climbing snowball (vs. the lace-cap bloom) hydrangea variety is available. After searching high and low, I am afraid that it seems that only white, lace-cap, climbing hydrangeas are available. These lacecap climbing hydrangeas (Hydrangea anomala subsp. petiolaris) are gorgeous plants, but unfortunately, do not fit your desire. You could also look for the Japanese climbing hydrangea: Schizophragma hydrangeoides ‘Moonlight’ (white), or Schizophragma hydrangeoides Rose Sensation (soft pink).

I hope that this has been helpful.

June 12, 2021