Gem progression as depicted in the discovery book
Gems are a currency used in Farm Merge Valley. They are obtained through 4-hour login in the shop, unlocking a new item in the Discovery Book, Reward Chests, and by collecting it from premium lands. Gems are movable and mergeable.
Gems can be used to buy resources such as Supplies, Energy, Reward Chest Keys and can finish the progress on Trees and Rocks instantly. They can also be used to buy Premium lands and rent a worker for 14 days.
Premium lands
You can also get Gems from Cards but only if you get lucky during the Card Merge, after you use a 3-star card any remaining star card of same plant/animal will be converted into gems.
3-star = 81+9 gems
2-star = 27+3 gems
1-star = 9+1 gems