Find poems in the public domain by searching collections at reputable sites such as Bartleby.com. This site includes anthologies and volumes of poetry that are in the public domain. Note that these are older poems, published before 1923, but they represent work by such masters as Robert Frost, Emily Dickinson, William Butler Yeats and Walt Whitman.
Research a poem that interests you to find out its publication date. If the poem was published in the United States before 1923, it is in the public domain. Most poems published outside the United States before 1923 are in the public domain as well. In addition, if a poem was published in the United States without a copyright notice between 1923 and 1997, the work is in the public domain.
Check poems published in the United States between 1923 and 1963 for copyright information. Works published during that time period could be copyrighted for 28 years. If the copyright wasn't renewed in the 28th year, the work fell into public domain.
Check poems published in the United States after 1922 but before March 1,1989 for copyright information. If the work was published without a copyright notice, the owner of the copyright authorized the publication, and there are no legal exceptions for the omission, the work falls into public domain.
Exercise caution with poems published between 1977 and 1989 and beyond. Copyright requirements become more complicated. The website for the Copyright Information Center at Cornell University provides a chart in PDF form called "Copyright Term and Public Domain in the United States" by Peter B. Hirtle. This chart offers a clear breakdown of public domain standards, a timeline of copyright changes and other vital information.