Why did Vincent Van Gogh draw Irises?

Irises was painted in the last year before his death in 1890, before his first attack at the asylum. He called the painting 'the lightning conductor for my illness' because he felt that he could keep himself from going insane by continuing to paint. To get to the answer, Irises was painted so van Gogh felt calm and serene. He needed or wanted to have a peaceful sense while he was in the asylum.