Plumeria seeds can remain viable relatively long, especially when stored in ideal conditions. Here’s a general guideline for the viability of Plumeria seeds:

1. Ideal Storage Conditions: When Plumeria seeds are kept in a dry and cool location, experiments by the Plumeria Society of America have shown they can remain viable for up to 10 years or even longer. These conditions help slow down the aging process of the seeds.
2. Reduced Viability Over Time: However, it’s important to note that the number of viable seeds may gradually reduce over the years when stored, even in ideal conditions. It’s been observed that the viability of Plumeria seeds may decrease by approximately 10% each year.
3. Testing Viability: To determine if older Plumeria seeds are still viable, you can perform a simple germination test. Plant a sample of the seeds and observe how many successfully germinate. If a significant portion of the seeds germinates, they are likely still viable.
4. Freshness Matters: While Plumeria seeds can have a long storage life, it’s generally advisable to use fresh seeds when available, as their germination rates are typically higher compared to older seeds.
5. Proper Storage: To maximize the longevity of Plumeria seeds, store them in a cool, dry place in an airtight container. Adding desiccant packets to absorb moisture can further help preserve their viability.
6. Label and Date: Always label your seed storage containers with the date of acquisition or harvest. This helps you keep track of their age and viability.

In summary, Plumeria seeds can remain viable for extended periods when stored under optimal conditions, but their germination rates may gradually decline. Performing germination tests can help you assess the viability of older seeds before attempting to grow them.