I water my plumeria often when they're in active growth. I try to keep the soil moist and never let it dry out, so when it's really hot outside I might have to water daily. That said, when I've been busy and haven't had a chance to water they've dried out and been fine. You really just want to make sure that you have a well-draining soil -- when you water you want the water to run straight through the soil and out the drainage holes, you don't want it to pool on top of the soil and be a sloppy muddy airless mess. Those glass bulbs won't hurt as long as the soil drains well! When the plants go dormant for their "dry season" I'll only water occasionally, like every three weeks or so.

Thanks Cervantes.

Thanks Cervantes.

It seems a big mistake most people make is thinking that the soil is dry or barely damp because it looks or feels dry/slightly damp at the top. The conditions of the soil can be much more moist or even saturated at the bottom of the pot. That being said plumeria are very drought tolerant, I have heard of many many people losing a plant due to over watering that leads to rot and don't think I have ever heard of someone losing a plant due to not enough water, so you are much better off leaning towards not enough water until you get a good feel for it. I feel the watering bulbs are a bad idea but maybe someone else on this forum has used them and can give a better answer on them.

Hong, Cervantes is right that the fast-draining soil is very important for any plumeria, big or small.

I wouldn't use one of those watering bulbs. The plumeria's trunk holds water in reserve and many growers prefer to let their trees' soil dry out before watering.

If you're not sure about the moisture level the easiest thing to do is drive a bamboo chopstick or skewer into the soil several inches deep and leave it. When you want to know if the soil is dry pull the chopstick out and if it's cool and dark the soil is still damp.