A Plumeria seedpod is ready for harvest when it has fully matured and started to split open. The seedpod will turn green or brown as it matures. Once it starts to split, it indicates that the seeds inside have reached maturity and are ready for collection. Gently touch the seedpod to ensure it has dried and is not still soft or green. Avoid harvesting seedpods that are still green or unripe, as the seeds inside may not be fully developed and may not germinate successfully. A ripe seedpod is a reliable sign that the seeds are ready for harvesting and subsequent propagation.