In Grass-based levels, your goal is to spread Grass across the entire Puzzle board. To do this, you must make matches where at least one of the matched Puzzle pieces is on a Grass-covered space while the other pieces in the match are on regular spaces, as shown below:
A great way to spread Grass is by using Boosters such as Rockets and Bombs. If a Booster is activated while on a Grass-covered space, it will spread Grass along its path!
However, Grass will not spread if there is an obstacle on top of it, even if you use a Booster to hit that space: