I guess your success with such strategies is going to be heavily dependent on whether the enemies can leap out or not. Any reasonably intelligent creature with enough strength is going to jump right out. Having plant growth restrain them so they can't jump is the real power, plus how wide it is. Something like grease is good if they fail their athletics check, but otherwise they'll just leap out and its value is gone. Now it's a hindrance to everyone on the field, including your party.