Gems are a premium-in-game item that is hard to obtain, they have several uses which includes unlocking dragons, costumes, and opening eggs instantly. Listed below are some ways you can get them for free.
Flying Purple Pigs
Eating the flying purple coloured pigs you encounter will give you one free gem but if there is trouble nearby it's not worth the effort to chase it.
Treasure Chests
Search for the treasure chests that are scattered throughout the game as they will give you gems and a decent amount of gold coins when you unlock them.
Stars
If you go beyond the clouds you will find stars that blink after every few seconds and transform into a food item or a gem. Using your boost you will be able to venture far and also discover treasure chests.
If you connect or link to Facebook you will be rewarded with 15 free gems.