It is not uncommon in the Ninjago fandom to joke about how Garmadon essentially replaced his kid with a plant. It's not uncommon for these jokes to make it seem like he likes the plant more than his son. I personally can't tell whether or not people actually think that, and, while it has no bearing on the real world, I had a thought about it. While Garmadon did essentially replace his kid with a plant, it's not because he didn't like his kid, or that he liked the plant more. It's because he still loves his kid, but due in large part to his own actions, his relationship with his kid has been damaged severely, and perhaps permanently. The plant is his outlet. This is acknowledged in episode 202: Brave But Foolish when, while talking about the plant, he says "It was the only green in my life. I had hoped it would grow, and thrive, and perhaps, one day, forgive me. But now it's gone, and I am alone."