The summer of 2013 was a very shady one here in north-central Georgia...and something very strange happened in our nursery and gardens: not only were the 'Dynamite' and other varieties of red flowering crape myrtles on our nursery and in our gardens blooming pink or white, we were getting feedback from customers in our area about how the red crape myrtles in their landscapes were doing the same.
I've been in the green industry business since 1980, but the first time I ever saw what I knew was a red flowering crape myrtle bloom white was in 2013. At that time 'Dynamite', a crape myrtle variety with the deepest true-red flowers of all crape myrtles, was blooming stark white in our gardens, and at the nursery. At first, we were totally baffled, but then we did a little research and found the cause.
What we found was that the flowers of some varieties of red crape myrtle, such as 'Dynamite', 'Red Rocket', 'Ruffled Red Magic' and 'Red Rooster' will open shades of pink or even white when they open during cloudy and overcast conditions. Apparently, full sun when the flower buds are opening is needed in order to bring out the full red flower pigment. If you open a flower bud on a Dynamite crape myrtle the petals inside will be white. The RED pigment is fixed in a
very brief period after opening (perhaps as little as 10 to 15 minutes). If the flowers open on a cloudy morning, they will be a distinctly lighter color. Likewise, if the plants are loaded on a truck one day then delivered the next day to a customer the flowers that opened in the absence of light will be white or light pink. This is NOT a problem as the next flowers that open in full sun will be cherry red. Also, both Dynamite® and Red Rocket® will occasionally produce a flower(s) with some white on the outer portion of the petals. This is normal during cool or cloudy periods.
For those of you who don't like the color change, the good news is that it's only a temporary condition as the plants will start blooming red again when they receive adequate sunlight. This often occurs during the same growing season if and when later blooms open on a sunnier day.
So now you know why red crape myrtles sometimes bloom pink or white, and this might mean you can stop thinking about digging up and replacing them. That said, if your red crape myrtle is in a shady location you might consider relocation to a sunnier site!
For more information on the flower color phenomenon check out this article published on Dr. Carl Whitcomb's website, who is the man that introduced 'Dynamite', 'Red Rocket', and many other crape myrtle varieties to the market.
Hope this info is helpful!