Lena Younger (Mama) demonstrates many of the characteristics of a traditional Idealist. Despite being widowed at a relatively young age, sharing her cramped apartment with two adult children, a daughter-in-law, and a grandson (who regularly argue), and facing opposition to her dreams, Lena remains an optimist. She believes that Walter will be responsible with the money she entrusts to him, even though he has done much to lose her trust. She thinks that Beneatha will put her college education to good use even though she constantly skips from one interest to another, and she trusts that buying a house--even if it is in an all-white, unwelcoming neighborhood--will bring her family closer together. This seemingly unwavering optimism is a key attribute of Idealism.
Similarly, Lena views nature as a teacher. Her plant is not simply an important symbol in the play. For Lena, the plant's progress or lack thereof mirrors her dreams for her family. She "studies" her plant to gain insight into her family's status.
Finally, like many other Idealists (and Romanticists), Lena views the city as a place which squelches dreams and corrupts her children. By moving into the suburbs, Lena thinks that her family will have a place to imagine, to feel, and to grow closer to one another.