Since they prefer moist, nutrient-rich soil, the areas where Petilil live are known to be good for growing Plants.
(From Bulbapedia) Petilil is a plant-like Pokémon that resembles a plant bulb, such as an onion. It is primarily light green. Its head is tipped with three oblong leaves that are very bitter. However, these leaves possess revitalizing effects. Its crescent-shaped white face, seemingly lacking of a nose or mouth, has brown eyes shaped like elongated ovals. A green "bib" is present on its neck, and its lower body consists of five stubs, two of which act as arms, and two more act as legs. It lives in areas with soil abundant in moisture and nutrients. This Pokémon is a female only species with no male counterpart.
The leaves on Petilili's head are bitter, but they can either revitalise a person who eats them or cause him/her to feel dizzy.
Petilil lives in places with nutritious and fertile soil.