Symbolism, Imagery, Allegory
Verbena doesn't really show up much until the last chapter, where it's not only in the title but plastered all over Drusilla and every page. But first things first… what's verbena? Don't worry; we've got your back. Verbena is lemony scented herb with cute little flowers.
Verbena also has medicinal uses. In the novel, it's strongly associated with Drusilla, who wears it constantly and even puts sprigs of it on Bayard when she gets the chance. Which kinda makes us wonder whether she's depressed or hysterical, since those are some of the conditions verbena is used to treat.
The last chapter, "An Odor of Verbena," is about John's death and Bayard's decision to step out of the violent cycle. But what it's really about is his feelings for Drusilla. The scene is set:
We rode on, toward the house where he would be lying in the parlor now, in his regimentals (sabre too) and where Drusilla would be waiting for me beneath all the festive glitter of the chandeliers, in the yellow ball gown and the sprig of verbena in her hair, holding the two loaded pistols. (7.1.13)
So we've got it all: death, beauty, ceremony, and violence. The verbena in Drusilla's hair would be giving off a lemony scent, and Bayard's thinking of her odor gives us the feeling he's into her as more than just a cousin. Or, er, stepmother. He's got sensual memories of Dru, and the verbena is the maximum example of that sensuality.
Later on we find out why Drusilla uses verbena: "she said verbena was the only scent you could smell above the smell of horses and courage and so it was the only one that was worth the wearing" (7.2.1). So when she was doing the man's work of soldiering, she would pick verbena flowers so that she could smell a little less man-tastic. Our little rebel does have a touch of girliness after all.
That touch of girliness is very important for Bayard, and it's the verbena that makes it happen. He might see Dru as one of the boys, but that little detail makes all the difference. One night, soon before his father's death, he goes for a walk with her:
I just knew that she was looking at me as she never had before and that the scent of the verbena in her hair seemed to have increased a hundred times, to have got a hundred times stronger, to be everywhere in the dusk in which something was about to happen which I had never dreamed of. Then she spoke. "Kiss me, Bayard." (7.2.13)
The verbena is what makes Dru into a woman for Bayard. It makes her an attractive being, not a relative, a tomboy, or a maternal figure. She's someone he wants to kiss. (Take note, those of you who are in the market for a new perfume.)
In the final moments of the novel, when Drusilla is sort of losing her mind over John's death and her desire for Bayard to take revenge, she does a kind of ritual with the verbena that doesn't really have a clear purpose. She gives Bayard one sprig of verbena, tucking it into his coat lapel, and crushes one in her hand. She tells him:
"There. One I give to you to wear tomorrow (it will not fade), the other I cast away, like this—" dropping the crushed bloom at her feet. "I abjure it. I abjure verbena forever more; I have smelled it above the odor of courage; that was all I wanted." (7.3.11)
This little ceremony, giving Bayard her scent to wear, is a way of sending him off to do her work. He is the one who has to be courageous now, because she's renouncing her warrior's life. The only problem is that he doesn't want to be a warrior either, so she's not going to be too happy with him in the end.
She leaves without saying goodbye, but she does leave a gift for Bayard. On his pillow, he finds "a single sprig of it... filling the room, the dusk, the evening with that odor which she said you could smell alone above the smell of horses" (7.4.36). The odor is so strongly related to Drusilla that Bayard can pretend she hasn't left.
Also, notice that here instead of saying that it's the only scent that covers up courage, he says horses. That might be because he wasn't courageous in Dru's eyes. Verbena is a feminine scent, but it's stronger than the odors of war. In many ways the women of this novel are stronger than the war, too, so the symbol is fitting of Drusilla.