Once There Were Greenfields (Japanese: ナタネとサボネア！さよならは誰のため！？Natane and Sabonea! Farewell to Whom!?) is the 54th episode of the Diamond & Pearl series, and the 520th episode of the Pokémon anime. It first aired in Japan on November 15, 2007 and in the United States on April 19, 2008.
Ash and his friends run into Gardenia, the Eterna Gym Leader, in the middle of her travels through Sinnoh. Gardenia is about to show off Pokémon battling with a friendly match, but Team Rocket interrupts to try and steal Pikachu! Of course, the minute Gardenia sees James' Cacnea, her love for Grass-type Pokémon blinds her to everything else, and suddenly James finds himself joining Gardenia in a tag battle against Ash and Dawn. Acting on Gardenia's advice, James has Cacnea try a new move, Drain Punch, but it only works once before Pachirisu and Aipom win the battle.
James turns down Gardenia's offer to train Cacnea, but it's still on his mind as he and Cacnea train hard to perfect this new move. Jessie and Meowth convince Ash and his friends to help Cacnea train, too! Dawn is understandably skeptical about helping Team Rocket power up, although Drain Punch still doesn't work even after Ash and his Pokémon help Cacnea train.
Gardenia returns in the middle of Cacnea's training battle against Ash's Aipom. Even though Cacnea battles with every last bit of its strength and beyond, it still can't pull off Drain Punch. Remorsefully realizing that he's just not skilled enough to bring out Cacnea's full potential, James stops the battle and tells Cacnea to go with Gardenia. He bids a tearful farewell to his Pokémon before running off, followed by Jessie and Meowth. But wherever he goes, James won't forget Cacnea and all their times together!
In Emeragrove Town, a group of young children come running out into a school yard and gather around Gardenia. Ash and his friends happen to walk by and notice her. They greet her and Brock launches into a romantic story of how they could be together, but he is abruptly stopped by Croagunk. Ash asks what brings Gardenia to the town and she explains that she is promoting battling by having battles all over the area.
Team Rocket watch from nearby bushes and decide to steal Pikachu the old-fashioned way. They race out into the open and perform their motto. Jessie then sends out Seviper and James sends out Cacnea, which grabs on to him. Ash asks Pikachu to use Thunderbolt, but before it can, Gardenia starts swooning over Cacnea, calling it "cute" and "cuddly". Dawn comments that Gardenia has never met a Grass-type which she has not fallen in love with. James takes Cacnea off her, telling her to grow her own Grass-type. Gardenia asks to borrow it, but James refuses. The children then remind Gardenia that she is supposed to show them a battle. Gardenia then persuades James to join her in a Tag Battle against Ash and Dawn, and Brock agrees to referee.
Gardenia sends out Turtwig alongside Cacnea to face Pachirisu and Aipom. Aipom starts with Swift, which hits Cacnea while Turtwig dodges. Cacnea then fights back with Pin Missile and Turtwig uses Leaf Storm. Both are dodged and Gardenia says that she has never seen such a gorgeous Pin Missile. Pachirisu uses Spark, which Turtwig dodges, before hitting Pachirisu with Bite. Pachirisu then uses Discharge, which is dodged by everyone except Cacnea. Aipom uses Focus Punch and Cacnea counters with Needle Arm, which breaks through the Focus Punch and hits Aipom. Meowth comments that the Needle Arm was surprisingly good and Gardenia suggests that Cacnea should use Needle Arm again. Pachirisu uses Spark and James tells Cacnea to counter with Needle Arm, but Pachirisu dodges and hits Cacnea. Aipom prepares to use Focus Punch, and Gardenia suggests James should tell Cacnea to use Drain Punch, and then explains how it is performed. James does so and Cacnea hits Aipom with a powerful Drain Punch, surprising everyone except Gardenia.
While Gardenia is distracted with Cacnea, Ash and Dawn take advantage, and a cry makes Gardenia remember Turtwig just as it is hit by Pachirisu's Spark, knocking it out. Aipom uses Swift and James calls for another Drain Punch, but the move fails and Cacnea is hit. Aipom then hits it with Focus Punch as it tries to use Drain Punch again, knocking Cacnea out and ending the battle. The children blame James for the loss. Gardenia says that she was right about Cacnea being strong enough to use Drain Punch. Dawn asks why it did not work the other times, and Cacnea explains it was an accident that it worked at all. Gardenia says that it was actually because James and Cacnea were not quite in sync. Gardenia then offers to train Cacnea, before heading to the Pokémon Center with the kids.
Later, James and Cacnea sit on a hill overlooking the town, depressed and thoughtful, when Jessie tells them to snap out of it. James then reveals that he is not sure whether to give Cacnea to Gardenia or not. Cacnea then says that it would like to learn to use Drain Punch. The "twerps" then return, and Jessie suggests getting them to help Cacnea train. James and Cacnea start training, making Dawn comment that Team Rocket do the right thing "once in a while", angering Jessie and Meowth. Ash and Pikachu offer to help them train, and while Dawn is doubtful, James and Cacnea are delighted. Pikachu uses Quick Attack, which Cacnea counters with Needle Arm. Pikachu uses Thunderbolt, which Cacnea dodges, causing it to hit James instead. Cacnea uses Needle Arm and Pikachu counters with Iron Tail, but Needle Arm breaks through it and hits Pikachu. Cacnea then tries Drain Punch, but it fails and Cacnea trips on a rock. Brock comments that their timing is still off.
Later, Cacnea uses Carnivine and Chimchar to practice punching. One of Cacnea's punches hits Chimchar in the face, so James tells it to use Drain Punch, but the resulting attack is not very strong. That evening, James goes back to pondering over whether to give Cacnea to Gardenia, and decides to have a training battle with Aipom. Gardenia comes up to watch. Aipom opens with Focus Punch, but Cacnea dodges and uses Needle Arm. They try again, but this time Cacnea misses and is hit by Focus Punch. Cacnea dodges another Focus Punch and counters with Needle Arm, before trying another Drain Punch, but it fails. Cacnea tries to counter repeated Focus Punches with Drain Punch, but is hit repeatedly. Cacnea ends up extremely tired, and still trying to continue, but James stops it. Making up his mind, he tells Cacnea to go with Gardenia, as he believes he will not let Cacnea reach its full potential. As he holds up Cacnea's Poké Ball, he fondly recalls his time it, and then says goodbye as he returns it. He then gives the Poké Ball to Gardenia and tells her to look after it, then runs off crying, with Jessie and Meowth in hot pursuit.
The next day at the Pokémon Center, the group says goodbye to Gardenia, with Turtwig and Cacnea by her side, while Team Rocket watch from the roof. James wishes one final goodbye to Cacnea from afar.
Gardenia states that Drain Punch is more powerful than Needle Arm. This was incorrect before Generation V, as Drain Punch and Needle Arm's base powers were tied at 60. However, it is possible Gardenia was referring to the fact that Drain Punch also restores the user's HP, thus making it more useful than Needle Arm.
Once again, the black part under Gardenia's mantle is invisible.