Is it not curious that the daughter of the dissolute and dissipated reprobate, Bob Ewell, is named Mayella Violet Ewell? There is clearly an indication that one of the parents--probably the mother--had a sensitive and artistic side that appreciated flowers. But, having no mother, Mayella can only grow the geraniums, a sturdy flower that emits a strong scent, much like a rose. Her geraniums are red, too, the color of passion and desire.
Mayella's pitiful attemps to beautify their trashy yard, as well as cover the odor with the scent of the geranium, indicate her search for some beauty in her ugly and lonely existence. Furthermore, her attempt to come into contact with someone--anyone--in her lonely and barren life is equally poignant.
The answer to this is that she grows geraniums. You can find this in Chapter 18. There, Scout is watching Mayella testify in the trial.
She says that Mayella looks like she tries to keep clean and be decent. Scout thinks that Mayella looks like she takes baths often. This is very different from how her dad looks. He looks like he just took his first bath in a long time so he could come to court.
When Scout sees this, she thinks of the red geraniums that she has seen in the Ewell's yard. These are the flowers that Mayella grows.
mayella grew many geraniums. she loved the smell and color.