No, not all Plumeria seeds germinate successfully. The germination success rate for Plumeria seeds can vary, and several factors influence whether a seed will germinate or not. Here are some factors that can affect the germination success of Plumeria seeds:

1. Seed Viability: The viability of the seeds plays a crucial role. Healthy, fully mature seeds harvested from ripe seedpods are more likely to germinate successfully than immature or damaged seeds.
2. Environmental Conditions: Providing the right environmental conditions, including warmth, humidity, and indirect sunlight, is essential for germination. If the conditions are not optimal, some seeds may fail to germinate.
3. Seed Variety: Different Plumeria varieties may have varying germination rates. Some varieties naturally produce seeds with higher germination rates than others.
4. Seed Storage: Properly storing seeds before planting helps maintain their viability. If seeds are stored incorrectly or for extended periods, their germination rates may decrease.
5. Seed Quality: The quality of seeds can vary even within the same seedpod. Some seeds may be more viable than others.
6. Infection and Disease: Fungal or bacterial infections can affect seed viability and lead to unsuccessful germination.
7. Insect Damage: Damage caused by insects or pests while the seeds are on the tree can reduce germination rates.
8. Injury during Harvest: Improper handling or damage to seeds during harvesting can also impact their ability to germinate.

Because of these factors, it’s common practice to plant multiple Plumeria seeds to increase the chances of successful germination. Even if not all seeds germinate, the ones that do can give rise to healthy Plumeria seedlings. Additionally, proper care and attention to environmental conditions can improve germination rates.