In Gardenscapes, the reward system works so that if you claim your rewards or view the reward notification, the countdown for Unlimited Lives and Boosters begins.
There are three Unlimited boosters: Rainbow Blast, Double Bombs, and lastly, Rainbow Blast and Dynamite. Once activated, they’re applied automatically to every level for the duration of the timer, so you don’t need to preselect them.
Tip:
To save rewards for later, claim them only when you’re ready to play.