The spike growth spell description states:
[...] When a creature moves into or within the area, it takes 2d4 piercing damage for every 5 feet it travels.
The transformation of the ground is camouflaged to look natural. Any creature that can't see the area at the time the spell is cast must make a Wisdom (Perception) check against your spell save DC to recognize the terrain as hazardous before entering it.
I'm uncertain how recognizing the terrain works:
- Does succeeding on the Wisdom (Perception) check reveal the entire area of effect, or only the square(s) you were about to enter?
- If you take damage from spike growth, are you now aware of the area of effect, or is it still camouflaged?