Not really an environmental thing but Hunger of Hadar(1/2 Movement & DOT) + Plant Growth (1/4 Movement) is basically a death trap covering a massive area for anything without Freedom of Movement.
Just be careful of candles otherwise your Plant Growth will turn into a massive fire ground hazard rather than Difficult Terrain.
Plant growth is insane area denial for things that can't teleport. Definitely have to be careful with fire spells cause the burning ground is so much less useful than restricting movement.