Q: I bought a “My Monet” weigela several years ago. It looks healthy and is growing well. I bought it for the variegated leaves, but for the past couple of years, the new growth is just plain green. What happened and will the leaves eventually turn white and pink like they are supposed to be?
A: Variegation is actually pretty cool. It is caused by genetic changes in plant cells. This can happen naturally from a spontaneous mutation or a viral infection. It can also be forced by plant breeders using chemicals or irradiation. The affected area is unable to produce chlorophyll, the stuff that makes a leaf green, so that area is white or yellow. The variegation can be over the whole plant or, in the case of a virus, just on part of a leaf or flower. Some of these changes are permanent. Others are less stable, and new growth wants to revert back to its all-green state. This reversion is more likely when a plant is stressed by extremes in temperatures or when it needs more light than it is receiving.
White or variegated leaves are not as robust as green ones. They need more light to compensate for the lack of chlorophyll, which is needed for photosynthesis, the turning of light into energy.
Your all-green leaves will not turn variegated. Cut out the green branches to their bases so they don’t overpower the weaker variegated branches. You may want see if you can increase the light the weigela is getting, either by trimming nearby plants or moving it. If a variegated plant is not getting enough light to photosynthesize, it will keep producing green leaves or will falter.
Genetically, when something has two different cell patterns in a part where it normally would have one, like in a multi-colored leaf or flower, it is called a chimera. Plant breeders take parts of chimeral tissue that have a desirable quality, such as an interesting color or better fruit, and propagate it to produce some of the plants and the produce that we buy. If you want to read an in-depth article on chimeras, see aggie-horticulture.tamu.edu/tisscult/Chimeras/chimeralec/chimeras.html.
Written by U of M Extension Master Gardeners in St. Louis County. Send questions to firstname.lastname@example.org.