Sun Locks

Sun Locks are a feature in Plants vs. Zombies: Collectors Edition and they have a grayscaled plant on them, with a sun amount below. These plants require the amount of sun to "unlock" then they act as a normal plant, you cannot plant on these plants, so you will need to shovel them if you want to replace it, however you can only shovel them upon unlocking them.

They sometimes appear in crazy daves choice and conveyor levels where they're usually overpriced, and in regular levels usually underpriced. Ask in the comments if you want this feature in your game.