To combine seeds and potions you need to put a water bottle on a slot. For example, if you want to make some Lunar seed, the recipe will be: Moonicite + Water + Seed
I know that the game isn't still intuitive, i'm working to fix that!
By the way you can try, if you wish, the remaked version of the game here, soon i will put on itch, but from now here's a link get the -full of bugs- game: https://twitter.com/MadSushiGames/status/996112652874199046
Thank you and see you soon!