Season 3 (15 episodes)

1. Season 3 - Episode 1 Doing the Backstroke

2. Season 3 - Episode 2 A Pool and His Money

3. Season 3 - Episode 3 The Brick Dance

4. Season 3 - Episode 4 Sh*t Highway

5. Season 3 - Episode 5 Bill Sussman

6. Season 3 - Episode 6 Grasshopper

7. Season 3 - Episode 7 He Taught Me How to Drive By

8. Season 3 - Episode 8 The Two Mrs. Scottsons

9. Season 3 - Episode 9 Release the Hounds

10. Season 3 - Episode 10 Roy Till Called

11. Season 3 - Episode 11 Cankles

12. Season 3 - Episode 12 The Dark Time

13. Season 3 - Episode 13 Risk

14. Season 3 - Episode 14 Protection

15. Season 3 - Episode 15 Go

The third season of Weeds begins with several subplots involving the fallout from the botched drug deal of the season two 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; in hiding, Sanjay realizes he is gay but is forced by U-Turn to have sex with a woman, who then becomes pregnant with his child.

The first half of the season sees Nancy under immense pressure as she works for U-Turn in order to pay off her debt, valued as the entire worth of the destroyed harvest. She gets a legitimate job working for Sullivan Groff (Matthew Modine), a crooked developer of rival neighboring community Majestic, and soon after begins a relationship with him, much to Celia's chagrin, as Groff had also started a relationship with her. Conrad and Heylia start their own new growing operation, initially at the behest of U-Turn.

The outlying Christian community of Majestic attempts 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 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. Dean has a motorcycle accident, which forces Celia to take care of him against her will.

Silas begins selling pot for his mother using the alias Judah and meets Tara (Mary-Kate Olsen), a born-again Christian who enjoys smoking pot and helps him sell; Shane and Isabelle become outcasts at the heavily religious Majestic summer school and form a friendship, and Shane begins talking to his dead father as the stress on the family becomes too great.

As U-Turn begins training Nancy to become his drug runner, while simultaneously starting a war with rival Mexican dealers, his partner Marvin becomes jealous. When U-Turn has a heart attack, Marvin capitalizes on the situation by secretly suffocating him to death and becoming boss of their crew, but after Marvin botches an attempt to call a truce with the Mexicans Nancy takes advantage of the situation to clear all debts for her and Conrad and end the gang war.

Finally debt-free, Nancy begins to feel lonely, and attempts to befriend Peter's ex-wife Valerie. The friendship turns sour when Valerie demands the money from Peter's life-insurance payout. Nancy promises to give it to her, but has to first use most of it to replace money Doug "borrowed" from the Agrestic treasury to help Nancy get back in business. 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 to not tell Valerie or the DEA for most of the remaining life-insurance money, which Nancy pays after ensuring 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 although Nancy has no obligation to give it to her, and that she no longer has it anyway thanks to Valerie's investigator.

Andy has a brief excursion into the pornographic film industry, and later befriends a group of bikers while trying to score with one of its members, who want him to start selling their weed.

Nancy turns to Guillermo (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's drastic solution of burning down the biker's grow house causes a huge fire in Agrestic which results in a mandatory evacuation order. Nancy has to face the possibility that she may have to start over from scratch and has failed her family as she forgoes to the idea that her deceased husband Judah is a spirit in the house, proclaiming that "she tried". In the final scene, she pours gasoline throughout her house and lights it with a match, ensuring that she and her family will be moving on.