the color Purple

As I look around at flower gardens in my backyard and in my neighborhood, I see a lot of purple.  Where the first flowers of spring seemed to be largely pink in color, the first flowers of summer seem to be mostly purple, a color that is not all that common in plants.  Why so much purple, and why now?

The intensely violet color of spiderwort flowers is on one end of the purple spectrum.

False Indigo flowers are another example of intensely dark purple color.

Purple is for the bees, and especially the solitary bees which are the most abundant and hearty pollinators we see in cool spring and early summer weather, before honeybees and butterflies have become active.  Bee eyes can detect light wavelengths in the ultraviolet part of the spectrum, and it seems that plants have adapted their floral displays to guide the bees right to the places on the flower where their search for nectar or pollen will do the flower the most good (i.e., pollination).

Streaks on the landing platform petal of the iris are probably visible to bees in the ultra-violet range.

One study with bumblebees in Germany showed that naive bees were highly attracted to flowers in the ultra-violet to blue range of wavelengths, and those flowers tended to produce more nectar or nectar with higher sugar concentrations than flowers of other colors.  Purple flowers that attract solitary bees tend to have the highest sugar concentration in their nectar (20-50% sugar), compared to yellow and red hummingbird and butterfly flowers that average around 20-22% sugar in the nectar.

The bell flower petals look homogeneously lilac to our eyes, but what do they look like to bees?

The variation in “purple-ness” of early summer flowers is due to the proportion of anthocyanin pigment in the flower in response to the pH of the soil environment.  In the presence of acid (or hydrogen ion), the pigment is red (or pink), whereas in the presence of nitrogen base the pigment is blue, and in the presence of aluminum, it is violet.   So, you can change the colors of your hydrangea or forget-me-nots by what you put in their soil.

Magenta-colored clematis flowers are the result of a redder expression of anthocyanin in a more acid cellular environment.

Flowers of this penstemon are pink-purple, based on the reaction of the anthocyanin in a more acid pH.

Bachelor’s Buttons, native of Europe, grows best in basic soils, which accounts for its deep blue color, and the bees seem to love it.

Purple is a coveted color in the garden, because of its rarity, and the ephemeral nature of purple flowers.  Looking back in our own history, we find that limited resources and the labor-intensive process used to create the color purple made it an expensive luxury, indulged in only by the most wealthy or by royalty.  Regardless of expense, its calming (blue overtones), yet energizing (red hues) make purple a favorite color.

14 thoughts on “the color Purple

    • Thanks — I’m so glad that you enjoy my musings. There are many, many things to wonder about each time I look out in the backyard.

  1. It is amusing how regional colors are. I suppose it makes sense in regard to what the local pollinators prefer, but even the foliar color in autumn is regional. There is not much purple here (in nature). We do have a preponderance of yellow and orange though.

    • You’re right, but I think a lot of what we see here is based on the strong seasonal effects on flowering. It’s hard to find these patterns in California (especially southern parts) because it is such an equitable climate (assuming there is enough water to grow) that everything grows well throughout most of the year.

      • Well, the native plants really do not bloom for long seasons in the wild. They bloom early, before the ground gets too dry. There is not much blooming in the summer in the chaparral or desert climates. Even in redwood forests, most native flowers are done blooming early. Native flowers bloom longer in landscapes only because they get water.

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