Dominance In Azalea Flower Color

You might recognize this Satsuki from a post earlier this year. Now it’s blooming. While that may be reason enough to share it, one of the curiosities of Satsuki is also evident: flower color dominance. 

Satsuki before growth and blooming cycle, April 2023. If you look closely, the flower buds that set last summer are everywhere.

Same azalea, two months later, June 2023. The cultivar is “Toyo”. 

Take a look at that lower left branch. All red flowers. There’s none of the shade complexity of the rest of the azalea.

Genetic mutation is displayed in flower color, an unusual and fun feature of azaleas. Understanding dominance makes it even more fun.

Red is dominant in azaleas, white is recessive. Because of the range of values in Satsuki colors, it’s easier to say to “darker is dominant to lighter”. Red is recessive to carmine, a dark red, for instance.

A light flower, recessive for azaleas.

A medium-value flower, mid-range in dominance.

And a red flower, out of these three the most dominant. This means, if you see a dark flower color like this, that shoot will never grow out and produce flowers lighter in color. 

An article on the inheritance of azalea flower colors spells out their complex dominance:

“Colour, whether it be purple, carmine red or red, is dominant over white. Red is dominant only over white. Carmine is dominant over red. Purple is dominant over carmine. Inversely, red is recessive to carmine, and carmine to purple. The order is, therefore, headed by purple followed by carmine red, red and white.”¹

All this asks the question: how does this change what we do with Satsuki bonsai?

If you’ve got a few azaleas you might keep eye out for dominance issues. Once a shoot heads down the dark path, those shoots won’t have light flowers again.

Old variable-color Satsuki, unmanaged, may end up with all dark flowers—purple or red. Pruning or labeling shoots at this time of year, while the plant is flowering, may help the retention of recessive characteristics. 

¹ Inheritance of flower colours and breeding of evergreen azaleas