I'm actually asking this because I want to mod tea into the game, but I wanted to hear from some lore experts on which regions would have the best climate for tea growing.

Akavir, I'm thinking.

Although, since tea is big in English culture, and High Rock is based on the British Isles, I'd say that's also an acceptable place of origin.

yes, based on the origin of realworld tea, it would likely from akavir
being exported to high rock, and became a custom among bretons

Thanks, I plum forgot about Akavir as a possible source. What about Yokuda? That seems like another good source of origin, with the Redgaurds bringing it with them to Hammerfell. Hammerfell is mostly desert though, but perhaps it would grow in the Dragontail mountains?

Redguards seem more like coffee drinkers.