The long, winding backstory: We have a rubber tree which has been in the same pot for ages. It has been moved twice, and in our new home we're still trying to find it a spot it likes. Recently, when we went to water it, we noticed standing water on top of the soil. It's been very droopy lately with leaves falling off. Thinking it's getting over-watered, we move it to get a bit more indirect sun and hold off watering for a while. Not much changes (maybe a bit more drooping). I start worrying about mildew and root rot, and as we're discussing what to do about it we realize it's been in the same pot/soil for probably over a decade. So I re-pot it in fresh soil and clean out it's pot. It's been about a week; and the rubber tree is starting (very slowly) to improve. Some wilted leaves are still falling off, but a few fresh green ones are starting to open. Now I'm worried about how to keep it happy.
Now that I have fresh soil in a nice large pot, I have the issue of keeping the water fresh. My past experience of plants is either in proper ground, or pots which can drain excess water. I understand I've just shocked this poor rubbery tree quite a bit, and I don't want to add more stress. But I feel there's a fine line between under-watering and over-watering when one leads to drought and the other to rot. We thought maybe a watering spike would help keep things even (as the water would be released about root level), then thought maybe that was a bad idea when the entire bottle emptied in about 18 hours. Now we figure there's a lake in the bottom of the pot, and we might be headed back where we started.
Rubber trees are very, very slow growing; and I'm not sure how quickly they take up water. Then again, maybe they like a bit of stagnant water in their pots. I've heard they very much like pots, at any rate.
My questions: In a sealed pot, how can I measure the water needs of my plant, and how can I make adjustments? Is there something I can do to protect the roots, or prevent water trapped in the bottom of the pot from causing health problems?