top of page

#BotanistLens: Al paints hydrangeas!

Boosting plant vigor is easy to do with many organic ingredients like eggs shells, coffee grounds and various other commercial plant foods that can be easily found over the counter. But what if we could boost flower color without having to use any complicated propagation techniques and creating a new hybrid?

Hydrangea flowers (inflorescence) are interesting wherein one can attempt to adjust the color by simply adjusting the soil pH.

Pink or blue, mop head hydrangeas can start as one color, but there is potential to alter the color of the blossoms by adjusting the soil. Most commonly known fact about color change in hydrangeas is that, if you change the pH, you can adjust the color. Higher pH (7.8 or higher) you get blue flowers and lower the pH (5.0 and below), there is potential to turn the flowers pink.

But new research shows that it is not the pH alone that does the trick. Hydrangea flowers (inflorescence) have sepals and not the usual petals. These sepals have a plant pigment called anthocyanin (delphinidin-3-monoglucoside). Anthocyanins are water soluble pigments and are the ones responsible for the red, blue, magenta and black colors in plants.

In Hydrangeas, when the anthocyanin binds with aluminum (Al3+ ) the sepals will turn blue. Al helps alter the color of the hydrangeas! "Hydrangea colors ultimately depend on the availability of aluminum ions (Al3+) within the soil. The role of aluminum has been known since the 1940s, but it did not reach the mainstream horticultural literature until about the past two decades, and the exact mechanism was only recently defined. Aluminum ions are mobile in acidic soil because of the ready availability of other ions they can react with, which can be taken up into the hydrangea to the bloom where they interact with the normally red pigment. But in neutral to basic soil, the ions combine with hydroxide ions to form immobile aluminum hydroxide" (

Here in the Mid-Atlantic we are lucky to be able to easily find blue hydrangeas and maintain that color as our native soils tend to be more acidic with sufficient levels of Al to maintain the pretty blue. In fact we have a difficult time maintaining pink flowers. For turning our blue hydrangeas pink, we need to make our soils more alkaline.

Want to give it a shot and see what Al in your soils could do, if you adjust the pH? To raise the soil pH, add lime and to decrease soil pH, add sulfur to the soil. Here is another neat article, if you want to try an alter the color of your hydrangeas:

Sharing with you today, a splendid color show of a mophead Hydrangea from Gresham. Its shows blue, pink and purple, all colors together on one plant and in some cases, the same head! A combination of these three colors on a single plant is an indicator of a nearby masonry foundation and a conglomeration of soils. Al's certainly having a hard time picking one color, its painting a rather unique and colorful happy canvas!

134 views0 comments


bottom of page