Garbage
From Petal Crashers Wiki
Garbage in various states of spawning.
Garbage blocks are blocks that cannot be moved by the player, but can be destroyed by clearing adjacent petals. They can be pre-placed on puzzle boards or sent to your opponent in VS. matches by clearing combos of larger than 2 petals, or chains. They spawn into the board after 4 turns, as opposed to normal petals, which take 8. As such, they can easily interrupt growing.