Lobelia flower pH spectrum

Colourful science

An extract of lobelia "Crystal Palace" acts as a pH indicator, turning pink in acid and turquoise blue in alkaline conditions.

Many blue/purple plants have this property as they contain anthocyanin pigments that react to the amount of acid in a solution. I find that the lobelia petals produce a particularly pleasing colour change.

Time for some kitchen science - raid the garden for blue/purple petals and mash each type up with a little hot water to release the colour. See if the colour changes when you add a few drops of lemon juice (acid), or sodium bicarbonate (weak alkali), or washing soda (alkali).

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