Plant Growth Spell
D&D Description of the Plant Growth Spell : Plant growth has different effects depending on the version chosen.
Overgrowth: This effect causes normal vegetation (grasses, briars, bushes, creepers, thistles, trees, vines) within long range (400 feet + 40 feet per caster level) to become thick and overgrown. The plants entwine to form a thicket or jungle that creatures must hack or force a way through. Speed drops to 5 feet, or 10 feet for Large or larger creatures. The area must have brush and trees in it for this spell to take effect.
Deeper info on this Dungeons & Dragons Plant Growth Spell