What determines hydrangea colors? Here's why you can have multiple colors on same plant

Hydrangeas one of the top ornamental plants in the country - but they have a special place in Cape Cod. Dubbed the signature plant of the area, the naturally acidic soil and mild winters of coastal regions are conducive to the growth and color of this popular perennial. There's even an annual hydrangea festival.

Coming in a variety of colors including blue, green, pink, purple, red and white, depending on the type, the hydrangeas are particularly vivid this summer.

But what determines this variety of colors in one plant? And how come sometimes different blooms on the same plant can be different colors?

Here's what to know.

What determines the color?

For most flowers, the answer is pigment, which comes from the flower itself. Wherever you plant it, assuming it survives, it will bloom the same color.

This is true for some varieties of hydrangeas, for example, white ones almost always bloom white.

But those popular blue bigleaf hydrangeas on the other hand, react to the acidity of the soil in the same manner as a litmus test, making it unique among plants.

And that depends largely on the soils acidity, with the petals working almost like a pH test strip, according to American Scientist.

Blue is when the shrub grows in acidic soil but develop red or pink when grown in neutral to basic soils, interestingly being the opposite of the colors for a litmus test (blue for basic).

More: Do your hydrangeas look great this year? Here's why this is a great year for blooms

Color goes beyond soil acidity, however, with the presence of aluminum being another important factor - acidity interacts with the aluminum to create a red or blue tone.

And if the roots are touching soils with different acidities, the plant can have different colored blooms throughout.

Can you change the color of hydrangea flowers?

By affecting the make-up of the soil, the levels of aluminum and acidity, the colors can be manipulated.

"However, such imposed red-to-blue or blue-to-red color changes do not happen instantaneously; it often takes one or two growing seasons to instill the desired color on shrubs within one’s flower gardens," according to American Scientist.

Experiments indicated a quicker change of red to blue could be induced by directly applying aluminum to the bloom as opposed to through the roots. To do this, scientist Henry Schreiber's team used a spray made from dissolved aluminum in a buffered citrate–citric acid solution, reducing the color change time down from two growing seasons to as little as several days.

New colors for hydrangeas?

Knowing the chemistry behind it, is this the dawn of a new era for the hydrangea community? Are designer hydrangeas on the horizon?

In a word? Theoretically. "The biochemistry of hydrangeas opens up the possibility of developing new colors that are both interesting scientific experiments and potentially beautiful additions to the garden," said Schreiber in the American Scientist article.

Yellows and oranges were once considered impossible due to the pigments in the plant, but the addition of the molybdate instead of aluminum ions to the stems of red blooms created a yellowing. This has opened the door to wilder ideas - like fluorescent (glow in the dark) plants, through the transfer of the fluorescent betaxanthin pigment from yellow flowers of the night-blooming four o’clocks (Mirabilis jalapa) and of portulacas to hydrangea blooms.

Long story short? You may be able to enjoy a hydrangea nightlight.

This article originally appeared on Telegram & Gazette: What determines hydrangea colors? It's a cool bit of science