A latchably closable horticultural capsule is configured to contain a growing medium, and to be temporarily closed around a branch section of a parent plant during an air-layering propagation process. The capsule includes a first shell portion and a second shell portion pivotally joined together by a central hinge. The first shell portion includes a main shell body having a cup-like shape configured to partially surround the branch section, the main shell body having opposed end walls with notches formed therein. The first shell portion also includes two seal-receiving cups externally attached to the end walls of the main shell body. The seal-receiving cups have hollow notches formed in respective edge portions thereof, and are also configured to partially surround the branch section. The notches of the seal-receiving cups are substantially linearly aligned with one another, and also with the notches of the main shell body.
