Question: How does the pH influence the color of flowers ?

Jennifer Bates answered on 15 Nov 2016:

Hi,

Some flowers are really affected by soil pH! Hydrangeas are the classic example of this, those big pink, blue, or purplish flower heads you sometimes see in gardens. In acidic soils they go blue, in alkali soils they go more pink. This is caused by anthocyanins, water-soluble pigments in plant cells that when stacked closer together appear blue. When you get more acidic soils aluminium in the soil is more water-soluble and the plant absorbs more and this allows anthocyanin molecules to move more closely together, so you get a more blue colour.

There are genetics that programme plant colours of course, unrelated to soil pH! So playing around with soil pH won’t always influence flower colour, and aluminium is toxic to plants so you don’t want to overdo it, keep the pH under tabs and if you desperately want different coloured hydrangeas, maybe talk to a specialist hydrangea gardener! 😉