I have grown Plumeria (frangipani) for 20+ years in Florida, Georgia and Maine. While easily grown in North Florida with occasional night time freezes, Georgia proved more challenging and finally Maine made it very interesting. But you can definitely grow Plumerias in most any location with a few rules. Plumerias are safe outside as long as the day and night time temperatures are above 50 degrees F. Once the temps start dropping below 50, the plant goes into dormancy. At that point watering should cease dramatically to almost drought conditions and the plant should be moved into an above freezing cooler location like a garage or unheated basement. The plant will drop all leaves and will be nothing more than leafless canes. While I have kept them all winter in an unheated basement, I have also kept them in a bright location in heated living quarters. Inside the house, the tree may maintain some leaves but still goes into dormancy. Obviously you will not be getting the blooms and active growth. It is important to restrict watering while the plant is in dormancy. Once outside temperatures warm above 50 degrees F, you can move the plant to a very bright, sunny location outside. Once the plant starts budding out again, you should resume watering. Remember Plumerias are tropical plants and thrive in high humidity, very warm to hot temperatures and prefer soils that are well draining and more on the sandy side. They definitely do not like being waterlogged and will most likely begin to root rot which will eventually cause the canes to rot as well.
Here in southern Maine, I once saw a 7 foot Plumeria in a doctor's office which they maintained year round in the office. The plant could not enjoy the outdoors in the summer because of being the size it was and located in a 5th floor commercial building. However, the plant always looked healthy and did bloom well. It was always located next to a large window with direct sun light most every day. So, with all that said, my experience and recommendation is to grow the plant on the dry side during the fall and winter, provide direct sun during the growing/flowering period, plant in well draining, sandy soil/potting mix, fertilize well during the growing period, water well during the growing period and definitely keep it indoors when temperatures drop to 50 degrees or below (day and night). Check for insects before bringing indoors and spray with Neem oil to prevent insect infestations before bringing indoors.
Happy Growing!
Hope this is helpful.
