window box

From King Dictionary of Contemporary English
Related topics: Gardening, Household
window boxˈwindow box noun [countable] DLGDHa long narrow box in which you can grow plants outside your window
Examples from the Corpus
window boxIf you don't have one, get a window box or hanging basket.There, perched on the window box with her nose glued to the other side of the glass, was Violet.