So, Opal's over at Gloria's house, and Gloria convinces her to plant a seed. Only she doesn't know what the seed is. Let's check this baby out:
What Gloria picked for me to grow was a tree. Or she said it was a tree. To me, it looked more like a plant. […]
"What kind of tree is it?" I asked Gloria Dump.
"It's a wait-and-see tree," she said.
"What's that mean?"
"It means you got to wait for it to grow up before you know what it is." (10.10-14)
It's just starting to grow.
It's figuring out what it will become.
Sounds a lot like Opal, right? (Except for the green part.) The tree also gives juicy hints into Opal's growth as a character:
(1) Why does she plant the seed? To see if "maybe [she] got her [mama's] green thumb" (10.8). She begins the story obsessed with her mama.
(2) Opal wants to come back the next day to see if it's grown, but Gloria says, "that tree ain't going to have changed much by tomorrow" (10.16). In other words, Opal's healing process (and maturation) takes time and patience.
(3) At the end of the story, Opal looks for her tree in the dark, and when she finds it, she is "surprised at how much it had grown. It was still small. It still looked more like a plant than a tree. But the leaves and branches felt strong and good and right" (26.3). Just like Opal—she's come a long way. She still misses her mom, but she's moving forward.
And that's good. And right.