A ventilated plant propagation assembly provides a propagation tray that supports plant life, and a dome that covers the plants. The assembly allows for selective control between a ventilated position that allows aeration inside the dome, and a sealed position that restricts aeration inside dome. The dome laterally slides, so that depressions at the dome edges selectively interlock with ribs at the tray edges. Thus, when the dome edge slides offset from the tray edge, the dome depression engages the tray ribs, creating a seal at the junction of tray and dome. Conversely, slidably aligning the dome with the tray urges the tray ribs against the dome flange. This pushes the dome up to create a gap between the tray flange and the flat surface of the dome flange. The gap enables aeration inside dome by creating a passageway for air to flow through the edges between dome and tray.