Just offhand, sounds like too much water. They like to be on the dry side, much like cactus. Especially if it's humid, they don't need too much water.

Hello,

These plants will drop old leaves periodically. Here in FL, my plants will start to drop the occasional bottom yellow leaf by about mid summer. How does the rest of the plant look... is this total defoliation in process or something less?

Hi here's a picture to see how the rest of the plant looks.
I never grown plumeria before, so I don't know their nature. At least its growing taller, but for every leaf gained it loses one.
I have had it on the dry side for a few weeks now.

this is a dropped yellowed leaf

It looks to me like your plant needs repotting into a larger pot. Since you're in S. Hemisphere, I don't think it's too late. Also, make sure it's getting some sun. But I don't know what your temperatures are like. Is it hot, hot there right now?

Hi Dave
I have repotted it about 3 weeks ago, into a very gritty sandy free draining mix.
It is in a conservatory under poly carbonate roofing and gets full sun most of the day, where its hot and mildly humid, day temps 35 to 40 C, night 20 to 25 C.

Hi Marcy....you're dealing with a bunch (mostly Americans)
who don't know diddly squat about Centigrade.

I had to do the conversion and thought others would probably
need it too, so here it is!

35 to 40 C is to us 95 to 104 F
20 to 25 C is to us 68 to 77 F

I think you might have not enough water. My plants drop
leaves when they're dry in summer. I give them a lot of
water in summer too and they grow like crazy. Of course,
they're in the ground and not in a pot like yours.

Is your growing medium really, really dry or is it moist.

It looks like you've got some fairly good sized leaves
on that plant too. That to me is a sign that the plant's
really trying to grow for you. Try a bit more water.

Hi

Sorry I should have figured that and provided conversions,
thanks........
I read a guys blog who had a huge collection of plumerias,(Texas) mostly in pots and he too recommended soaking them in a free draining mix each day during the summer,
When I first received the plant a couple of months ago I gave it a good watering every day, once it leafed up.
The problem of the falling leaves happen after it got about 3 - 4 leaves on each stem, on the 4th - 5th leaf it drops.
Some people suggested treating it more like a cactus, so I put in in a bucket size pot with a really gritty mix, and watered it lightly every second day, Its on the dry side,very slightly damp about 1/2 " down now.
The result is still the same, but its growing slower , so dropping leaves slower, its mid summer.
Doesn't seem to have made much difference between lots or little water, to the yellowing, which is why I thought perhaps it could be some kind of virus, but I couldn't find any matches.
The leaves are a good size 5 -7" on a 2' plant, and your right, the new growth is vigorous and healthy.
Its my first plumeria, so I really don't know what to expect.

Does anyone know what the brown on the edge of the leaves in the top picture is caused by ? I have the exact same thing on the leaves on my three plants and this is the only picture I have been able to find that shows the condition. I'm in zone 10b Southern California. THANKS !!