Can my plants with red leaves still do photosynthesis?

As red as your plant's leaves may be, they certainly contain chlorophyll as well. All plant leaves have this green pigment, and almost no plant can live without it, as it is what captures light from the sun and stores its energy in combinations of carbon dioxide and water. Some weird bacteria can capture light energy without chlorophyll, but that's a longer story and not really relevant for your garden!

But, I hear you insist, the leaves of my coleus really aren't green! Actually, underneath a lot of red they really are. What you're seeing is a combination of the green color of chlorophyll and very strong red colors from pigments of various kinds including flavins and carotenoids.

These sorts of pigment are usually present to varying degrees in all the "green" leaves you are more used to, and only tend to be seen in the fall when the cholorophyll, which is less stable, breaks down enough to reveal the other colors. They are all biologically important and play all sorts of roles, including offering protection against oxidative damage and control of biochemical reactions in the plant.

Most of the time, making such nongreen pigments is a waste of energy for a plant. They tend to be less efficient than proper green plants, and there are arguments that most of the species that wind up in gardens really survive the competition with green plants since people like the way they look and take care of them.

Dr. Knowledge is written by physicists Stephen Reucroft and John Swain, both of Northeastern University. E-mail questions to drknowledge@globe.com or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.