In which chapter does Mayella Ewell tend to her geraniums, and which chapter tells mainly about her and her background?

We learn about Mayella Ewell when the trial starts.  A description of the Ewell home is given in Chapter 17. It is a very run down property.

"The varmints had a lean time of it, for the Ewells gave the dump a thorough gleaning every day, and the fruits of their industry (those that were not eaten) made the plot of ground around the cabin look like the playhouse of an insane child...” (pg 170)

However, there were some red geraniums growing in one corner of the yard,

“...cared for as tenderly as if they belonged to Miss Maudie Atkinson...People said they were Mayella Ewell’s” (pg 171).

The reader learns about Mayella in Chaper 18.  This is when Mayella is called to the stand to testify against Tom Robinson.  Scout gives some background information she knows from living in Maycomb, and Mayella is asked some personal questions by Atticus to give the jury some background information.  Mayella is 19 years old and is the oldest of seven children.  Her mother is deceased.  She has two to three years of formal schooling and can read and write as well as her father, which isn’t saying much. They were on welfare, but the check wasn’t enough to feed the family, and her father was a drunk . They had to haul water from a spring that ran near their home, and they used old tires to make shoes when they needed them.  Mayella has no friends and when asked why by Atticus, Mayella thinks Atticus was making fun of her.  All of this information can be found on page 183 of the book.