Common or garden

This adjectival phrase means ordinary in the sense of describing something or someone as undistingushed and hardly worth a comment. The expression is first cited by to the OED, in 1657 when it was used to describe 'the common or garden nightingale'. The 'common' referred to is common, open land. For example, a common or garden plant is something one would expect to find on common, open land or in one’s garden, growing without any cultivation.