When you first plant the seed the guy next to the portal gave you, it's in a secret little cranny to the right of that upward climb! Maybe you'll have more luck than I will with making it work
Wait nevermind, I managed to find it! Use the shell gem on the vending machine in the club house, That is the pink one. The red one is used for something else.
Oh man no wonder I was fumbling around. I must not have even realized I grabbed the real pink seed in my first playthrough! I didn't even register the other pot was red :')
