As they continue their journey towards the Cinnabar Gym, Ash and his friends come across a Hiker who challenges Ash to a battle, which he gladly accepts. The Hiker sends out his Rhyhorn while Ash counters with Bulbasaur. Rhyhorn executes a Take Down, the ground shaking as it charges right at Ash's Bulbasaur, with Pikachu not liking the outcome. Ash commands Bulbasaur to use Leech Seed, but Rhyhorn closes in and sends Bulbasaur flying before the attack is launched. Ash tries to recall Bulbasaur, but Bulbasaur refuses. Brock states that it will not back down until it wins and it seems that Bulbasaur really wants to battle it. The Hiker says that Ash must be a bad Trainer if his own Pokémon does not listen when told to return it to its Poké Ball. Rhyhorn charges again, but Bulbasaur's Razor Leaf stops its rampage and follows it up with a Vine Whip. Rhyhorn collapses, giving Ash the victory, and the Hiker commends Ash for training his Bulbasaur well. Ash then notices that his Bulbasaur cannot get up and its bulb begins pulsating with a blue glow.
They rush Bulbasaur to the nearest Pokémon Center, where Ash informs Nurse Joy of the situation. Nurse Joy eventually informs him that Bulbasaur is not sick at all and is instead almost ready to evolve. Bulbasaur appears disgruntled despite Ash's enthusiasm. Nurse Joy tells Ash that it will evolve at a special festival.
As everyone is asleep at the Pokémon Center, a long line of Bulbasaur appear outside. Ash's Bulbasaur gets up and walks outside, watching the view of the sparkling flowers and the full moon, with Pikachu accompanying him. Suddenly, a group of Bulbasaur use their vines and grabs Bulbasaur, taking it towards the forest. Pikachu initially gives chase, though its efforts prove fruitless. At Bulbasaur's request, Pikachu then heads back to the Pokémon Center to wake up Ash and the others. Pikachu informs them of what happened and they decide to follow him to find Bulbasaur.
Elsewhere, Jessie enjoys the view of sparkling flowers, but James disagrees as he has allergies. Suddenly, they walk right past the group of Bulbasaur holding Ash's. Jessie says they should capture them, but they all hit them with their vines and sends the trio blasting off.
As the group continues to follow Pikachu, Brock notices a trail of pollen and suggests they follow it, with the hope that it will lead to Ash's Bulbasaur. Suddenly, the roots of a group of trees start thrashing around and then tangle together to form a barrier. Getting through it, the group gaze upon the garden, where they find thousands of Bulbasaur. They chant and the central tree's branches grow, complete with foliage. The tree's hollow then glows intensely and a Venusaur emerges and climbs on a tree stump. The gang searches for Ash's Bulbasaur, with Misty pointing out that it has a bandage on its head. They manage to find it, but Brock reminds Ash that humans have never been in this garden before. All of the Bulbasaur are happy except for Ash's. The Venusaur roars and the Bulbasaur follow suit. This continues several times before all of the Bulbasaur's bulbs begin to glow.
Team Rocket reappears, though they cannot get through the wall of vines. James asks Meowth to scratch his way through, though Meowth says that he just had his claws filed. Jessie and James promptly get out an ax and a saw, whilst Meowth holds a pair of scythes. However, the vines begin to attack and chase them away.
In the garden, the Bulbasaur begin to evolve into Ivysaur. Brock comments that people have always disagreed whether Bulbasaur is a plant or an animal, and says that Bulbasaur might be a symbol that all life on Earth is connected. Just then, Ash notices that his Bulbasaur is struggling to refuse the evolution, which enrages Venusaur and all of the Ivysaur. Venusaur is about to hit Bulbasaur with its Vine Whip, but Ash rushes in front of it and takes the hit to his shoulders. Ash apologizes for coming to their festival, but states that Bulbasaur is his friend. He asks if they are mad that Bulbasaur will not evolve, and they all nod. Ash says that if Bulbasaur does not want to evolve, they cannot force it to. Venusaur roars, sending pollen to the tree, which bursts out in red flowers, the vibrant display easily impressing Ash and his friends. Misty points out that it was manipulating nature and points out to Bulbasaur that if it evolves, it could do that too, but it still refuses to evolve. Ash apologizes to Bulbasaur for not considering its feelings on the matter, and it smiles at the acknowledgement.
Suddenly, Team Rocket arrives in their balloon and being sucking up the Ivysaur into a bag. Pikachu begins to fly upwards, but Bulbasaur catches him with its vine and pulls him to safety. Ash tells Bulbasaur to knock Team Rocket out of the sky, and Bulbasaur tries using Razor Leaf, but it fails. James asks if they should get Bulbasaur, and Jessie and Meowth just laugh, saying Bulbasaur is a wimp. Bulbasaur shouts and the sun suddenly rises over the horizon, its rays entering through the opening on the top of its bulb. Ash consults with his Pokédex, which says that it was getting ready to use Solar Beam. Bulbasaur then releases a beam of energy towards Team Rocket, hitting the vacuum bag first before piercing the balloon. It explodes, and Bulbasaur frees all of the Ivysaur with Razor Leaf, while Team Rocket falls to the ground in their basket. All of the Pokémon strike Team Rocket all at once with their vines, blasting them off again.
Ash says Bulbasaur did great, with Venusaur agreeing, before smiling and extending a vine. Bulbasaur extends its vine and connects with Venusaur as a sign of respect. The vine barrier pulls away, and as Ash and the others are about to leave, they notice that the garden has disappeared. They then wave goodbye to Venusaur and Ivysaur.