Weeds is an American television comedy on the Showtime cable network created by Jenji Kohan. The central character is Nancy Botwin (Mary-Louise Parker), a widowed mother of two boys who begins selling marijuana to support her family after her husband abruptly dies. Over the course of the show, she and her family become more entangled in illegal activities.

Weeds Season 3 begins with the fallout from the botched drug deal of the season 2 finale: Celia finds and destroys the entire harvest; U-Turn pays the mobsters to leave Nancy to him alone; Silas is arrested and sentenced to community service; Sanjay (Maulik Pancholy), comes out of the closet, but U-Turn forces him to have sex with a woman who becomes pregnant with his child. During season 3, Silas and Shane remain the same age, however, as the series goes on Shane turns 12.

In Weeds Season 3, during the first half of the season, Nancy works to pay off her debt to U-Turn based on Celia's destruction of an entire pot harvest and U-Turn saving her life. Nancy also gets a legitimate job working for Sullivan Groff (Matthew Modine), a crooked developer from the neighboring community of Majestic, and she soon becomes his lover. Celia, who has also been intimate with Groff, resents Nancy for this.

Silas begins selling pot for his mother using the alias Judah and meets Tara (Mary-Kate Olsen), an evangelical Christian who enjoys smoking pot and helps him sell it too. Shane and Isabelle become outcasts at the heavily-religious Majestic summer school and form a friendship. Shane is also having conversations with his dead father, who he insists is really there, as familial stress increases. Nancy gets called in by the DEA, and is terrified that she is being busted. But it turns out that they've found out about her marriage to Peter Scottson, and have a hefty life insurance policy to give her.
At U-Turn's behest, Conrad and Heylia start a grow business. U-Turn sees talent in Nancy and trains her to be his lieutenant, while simultaneously starting a war with rival Mexican dealers. When U-Turn has a heart attack while jogging, Marvin suffocates him to death and becomes the new boss of U-Turn's crew. Marvin botches an attempted truce with the Mexicans, allowing Nancy to clear all debts for her and Conrad and end the gang war.

Debt-free, but feeling lonely, Nancy attempts to befriend Peter's ex-wife, Valerie. The two bond over their troubled lives. Their friendship turns sour when Valerie demands the money from Peter's life-insurance payout, which she feels she has earned by her years married to him and the child they have together. Nancy promises to give it to her, but has to first use most of it to replace the money Doug "borrowed" from the Agrestic treasury to help Nancy get back in business, pay his divorce lawyer, and get laser eye surgery. Despite giving her several smaller payments, Valerie believes that Nancy will never give her her full due and that Peter had an off-the-books stash of cash of which Nancy knows the location, so she hires a private investigator to trail Nancy. The investigator finds out Nancy is a drug dealer and blackmails her for most of the remaining life-insurance money in exchange for not telling Valerie or the DEA. Nancy pays the money but ensures the investigator won't come after her again by blackmailing him for blackmailing her. Nancy confronts Valerie by telling her that she would have gotten the money despite Nancy having no obligation to give it to her, but that now, due to Valerie's investigator, Nancy no longer has any money to give Valerie.

Meanwhile, the nearby Christian community of Majestic has been attempting a hostile takeover of Agrestic, with Doug leading the charge due to the large amount of money it will bring in. But Groff's gift—a new house in Majestic—to Celia leads to jealousy, and Doug begins sabotaging the Majestic city infrastructure, although it is already too late, as Celia brings it to a public referendum. To get back at Groff, Doug steals the giant cross from Majestic's megachurch, eventually putting it inside the grow house. Meanwhile, Dean has a motorcycle accident, which forces Celia to take care of him against her will. Heylia and Conrad are forced to move the grow operation and Nancy negotiates the use of Celia's off-the-books house in Majestic. Andy has a brief excursion into the pornographic film industry, also at Celia's off-the-books house, and later befriends a group of bikers while trying to score with one of its female members; they want him to start selling their weed. Nancy and Conrad become lovers while hanging out at the grow house, but Conrad realizes he has no future with her. Nancy turns to Guillermo—the leader of the Mexican dealers—to get protection when the bikers threaten her family after she refuses to sell their low-quality "ditch weed". Guillermo decides to burn down the bikers' marijuana field, causing a huge fire which spreads to the Agrestic area. At that time, thermal cameras spot the stolen cross and the DEA moves in.

Nancy, meanwhile, takes advantage of the fire and pours gasoline throughout her house and lights it with a match, ensuring that she and her family will be leaving and moving on, and there will be no evidence of their drug activities.