Grass-type Pokémon are usually calm, pacifistic, and like to take care of flowers, plants and nature itself, but are also great fighters and can poison, paralyze or put targets to sleep. Most of the times, the Pokémon have part of a plant, thus their growth is really similar to that of a plant. Some of them also grow berries, flowers and leaves, and many of them can control their growth.
Grass-type Pokémon usually have combinations with the Bug and Poison types. The last one is because many plants are poisonous. The Grass type is the type that has most weaknesses (along with Rock). The best type moves a Grass-type Pokémon can learn is Rock, because it covers 4 of its 5 weaknesses (Bug, Fire, Flying and Ice).
Famous Grass-type Pokémon Trainers include Erika, fourth Gym Leader of the Kanto region; Gardenia, the second Gym Leader of Sinnoh; Cilan, one of the three Striaton Gym Leaders in Unova; and Ramos, the fourth Gym Leader of the Kalos region.