The tutorial is built into the game, mechanics are shown by playing the game in a basic way. For example: The mechanic of the plant always growing is shown in the first level, and the mechanic of the plant cutting itself shorter on platforms is shown in the second level by a player doing the most likely thing, (moving to the right.) And then later the mechanic of not growing if standing on stone is shown by forcing the player to stand on stone.
Admittedly this might not be the clearest, (it was a game made by a whole discord server all at once) but to be honest, it's the best way to implement tutorials because the player feels like they are discovering the mechanics instead of being told what they are.