Got a Plumeria back in July, it's my first time trying my hand at this plant and all seemed to be going well but over the past few months, it's been developing some yellowing leaves. At first, I thought it might be overwatered so I cut back from watering it every day to watering it every-other-day. Now, however I'm thinking it might be heat stress. The plant receives full sunlight and back in July-Sept, we had some very hot days in the triple digits. Now it's usually in the 80s so a bit milder but still gets in the 90s on some afternoons. What do you think is happening? I have seen some other Plumerias in my area and they look very healthy so I'm at a bit of a loss. I attached an image so hopefully I can figure out whats going on.

Is there a drain hole in that pot? It looks over watered, but you are a couple of zones below me, so it may just be going dormant. Mine bloomed really late this year, but are shedding leaves even when in full bloom. I can't tell if those are mealy bugs in the photo, or just latex bleeding from a damaged leaf.

The pot definitely has drainage holes, and upon closer inspection I don't think that white/brown spot is bugs. If it is overwatering, how often should I be watering it? I usually use a soil moisture meter but I still end up watering it every-other-day.

Do Plumerias always go dormant? Where I live it rarely gets below 45 F during the winter (40 at the lowest at night), and its usually in the 60s during the day?

Too much water for the season! It's fall, and they are supposed to go dormant. Zone 9a doesn't tell me much accept when you get a freeze. That's useless in So.Cal! Go online and lookup your "Sunset Western Garden " zone. Depending on where you are, your Plumerias are ready to go dormant. Unless you are in one of the current fire zones ( read high winds) your Plumerias shouldn't need water that often. I'm coastal zone so mine (in pots)get twice a week, depending on temps and winds. In ground are lucky if they get once a week water. But to answer your last question, Yes! Unless you have a south facing garden room, they will loose all their leaves. Dormant, less water! Folks in cold zones dig them up and store them [Bare Root] for the winter! I just sent you a tree mail. Check the envelope at the top of the home page.

I looked up my sunset zone it's either zone 18 or 19. (I live in Upland, CA) These plumerias sit outside but are in the backyard - which faces south and has no trees or other sources of shade, so they get continuous sunlight all day long. Anyway. Thank you so much for your help!