Dahlia Heimertz, also known as Madame Dahlia or simply Dahlia, is the Heimertz Family Circus's former "Plant Tamer", the wife of Ronan Heimertz, and a mentor to Ellen. She was orphaned at a young age and lived in the streets until she joined the Heimertz Family Circus. She is stout, kind, gentle and motherly and knows when to be firm.
When Madame Dahlia was a young girl her parents died of unknown causes and had to live in the streets until the Heimertz Family Circus adopted her, with them she travelled all over the world and collected all kind of plants, besides forming a close bond with Ronan Heimertz until he was selected to resguard the balm that lied under the twins' home in Nod's Limbs.
Madame Dahlia reunited with Heimertz when the circus returned to Nod's Limbs and helped him hide from his family while he tried to dig up balm to cure a dying Pet. In the meantime she meets Edgar and Ellen when she realizes that Ellen, Imogen and Gonzalo arranged one of the midway's games and intervened before Stephanie could get the children in trouble by giving Stephanie a prize and announcing that she had won so the crowd so carry her away. Dahlia scolded Ellen for cheating and ordered her, Imogen and Gonzalo to gather their friends and go to her tent, where she attempted to use her Nepenthes Leviathos, Gustav to scare Ellen into behaving by making her believe she was going to let the plant swallow her, although it didn't work since Ellen knew Leviathos don't eat humans, which impressed Dahlia. She shared some of her past with Ellen and took the children to her living quarters, where she told them the story of Mad Duke to teach them that greed was no game.
While hiding in Dahlia's tent, Edgar and Ellen found out that Dahlia had been helping Ronan hide from his family before Pollyanna entered Dahlia's tent. The puppeter finds the fake ambers that the twins had taken from her puppet house and chewed out Dahlia for helping Ronan and claimed that she was going to tell Benedict so that she, Ronan and her "nasty little plants" could be banished from the family. Dahlia then goes to her show, where she ends up rescuing Ellen from Gustav's stomach after the plant swallowed her, although Dahlia was able to pass it off as part of her act. While the crowd cheered, Dahlia taunted Ellen by telling her to "leave [Gustav] to ones with true green thumb".
Dahlia was forced to flee from the Big Top along with everyone when the tent collapsed. Manny ordered Officers Jibbers and Jabbers to arrest her after Pollyanna told him Dahlia had been helping Ronan the whole time. Both Dahlia and Ronan were locked in a gorilla cage, where she attemped one last time to reason with the twins, although to no avail. ("High Wire")
When Heimertz receives Ellen's letter, the couple escapes from their family and return to Nod's Limbs. Madame Dahlia stays at Heimertz's Shed with Pet while he rescued the twins, Nod and Miles and later tended to his wounds. ("Nod's Limbs")
Madame Dahlia and Heimertz help the twins build a float for the Prank You Very Much Day's parade. They get married the next day and immediately depart on Nod's blimp to Bavaria to make amends with their family. Once they arrive to the circus, they find out that the whole family disappeared. Madame Dahlia returns to Nod's Limbs to warn everyone and she and Nod leave to find the Heimertzes. ("Hot Air")
Eventually, Stephanie found her and Nod. She hypnotized them with Ithune's tears and ordered them to hypnotize Ellen, although they didn't success. After that, Stephanie orders them to drown her and Archibald Tibbits in Lach Lufless's lake, although they are able to escape and Ellen makes them ingest Nepenthes' seeds, freeing them from Stephanie's control. Later Madame Dahlia departed with Nod, the twins and Pet to Zimmizoka. ("Split Ends")
Madame Dahlia is a sizable woman with long, full bodied black hair, which she normally wears up in a tight bun or ponytail, an oval-shaped face and an upturned, pointly nose. Since Dahlia isn't blood-related to the Heimertzes, her smile is average. She also has very strong arms due to years of taming savage plants for the circus. In Hot Air it is revealed that Dahlia has dark colored eyes. Her age is unknown, although she has stated that she isn't young anymore.
She usually wears a tiered dress with puffy sleevess, rings on all her fingers except her thumbs, three bracelets on her right arm and a pearl bracelet on her left arm. For her show, Dahlia wore a long, sleeveless, V-neck emerald sequins dress that was torn at the ends and hide her feet from view, her hair down, earrings and gloves. Her wedding dress consisted in a handmade sea green gown with a slim band of blue jewels sewn down on the side and wore her hair in a ponytail.
Madame Dahlia is brave, loyal, well-mannered, and caring, unafraid to stand up for herself. She can go to great lengths and take high risks in order to help her loved ones. When first introduced, Madame Dahlia showed a cold attitude, possibly due to being separated from Heimertz for twelve years.
- Dahlia is also the name of a flower.
- In the Victorian language of flowers, Dahlia denotes elegance and dignity.
- Madame Dahlia seems to really like the color green as the dress she wore in her show, her wedding dress and the dress she made for Ellen were green.
- Madame Dahlia is the only known member of the Heimertz Family Circus to speak in broken English.
- Madame Dahlia calls people by their birth names.
- Madame Dahlia and Benedict Heimertz are the only ones who call Nod by his first name.