Check out this article, it has some good information on Plumeria care

Did you plant your Plumeria cutting, expecting many large and fragrant blossoms, but after a whole year you still have nothing to show for your hard work? What’s up with that? Is there something wrong with my plant you might ask. Well many people think they can just plant thier new cutting, water and let the sun do the rest. For the most part, this is correct, but you are missing one big ingredient.

Fertilization is a very important part of growing a healthy and prolific bloomer. There are several opinions about what kind of fertilizer to use but the most common thought is that a fertilizer high in phosphorous is the best kind when it comes to encouraging flowers and branching. Most any brand is fine but the type you want usually will be called Super Bloom something or other. This is because the high phosphorous or middle number encourages flowering. So look for a number on the fertilizer like 10-50-10.

Granuals are ok but a liquid fertilizer or graduals that mix in water to create a liquid application are best. This is because you know exactly how much fertilizer you have added and when it was absorbed. If you put time release graduals in the pot, you don’t have as much control over the actual delivery of nutrients. Its kind of up to how often you water and how much you water. In any case, either one is good and better than nothing at all.

Be sure to water your plant first then come back around with the fertilizer. This is true whether you use a gradual or liquid fertilizer. This helps prevent burn to the root system. If you give straight fertilizer without first watering, the application can be too strong and burn the roots.

Follow the instructions on the label of the particular brand you are using when it comes to an application schedule.

Another trick is to supplement your feed program with some Epsom Salt. Add a tablespoon of salt to a gallon of water. Apply a good soaking to your Plumeria once a month. Epsom salt add several trace minerals to your Plumerias diet that are essential for healthy growth.