Flowers Changing Color??

On Saturday, a caller wondered why her Lily of the Nile (agapanthus) would be a lighter color blue this year than last year. I was reminded of a caller earlier in the year who had the same complaint about a favorite, deep-red rhododendron.

Yes, there are many red rhodies and agapanthus from pale blue to purple. But, right from the start, we’re going to assume that these gardeners have good memories and do know what color the flowers were last year. None of that eye-rolling!

So, what might be the explanation? Flower, leaf, and stem colors come from combinations of pigments made by the plant – delphinidin (blue-violet), carotenoids (for yellows), anthocyanins (reds), and, of course, chlorophyll (the many greens).

This explains why we don’t have a blue rose (there are no blue pigments in the rose family) and why some hydrangeas stay white (they have no pink and no blue). But once we the colors are present in the plant – what determines the intensity of those colors?

The complex system that produces the colored pigments depends on the presence of specific nutrients. If these are lacking, the plant may not be able to make enough compounds to give the deepest color. This is a good reason to use compost or natural plant foods, which are always rich in a wide array of essential nutrients.

Temperature can impact color, too. The lower the night temperature, the less intense the flower color is. So, warmer spring nights or cooler summer nights would be a factor that differs from year to year.

And light – that variable and varying Northwest commodity. A high amount and intensity of light builds up the colored pigments in plant leaves and flowers. Our famous cloud cover during critical times could also change the flower display from one year to the next.

So, keep your plants in good health and nutrition. The amount of light and the season’s temperature are nothing we can control. Let’s enjoy whatever Nature brings us.

Thanks to Phillip W. Simon (University of Wisconsin), Dr. Leonard P. Perry (University of Vermont), Dick Bir (North Carolina State University), researchers at Texas A&M University, and the dahlia genetics group at Stanford University for their work on the biochemistry of color in the plant world.