Why are the leaves on my Acacia Dealbata falling off?

I bought a Acadia Dealbata a few weeks ago, but since it was still too cold to place outside (the label said it needed a temp. of min. 4 Celcius), I've put it in my living room. The room is generally warm, but not hot and certainly not cold. I've kept the plant watered, although it seems to dry out really quickly, making it hard to keep up with (I guess I've ended up watering it three times a week). Unfortunately we don't get much sun in our living room, so maybe that's the problem. However all my other plants don't seem to suffer from the 2-3 hours a day filtered sun-light light. Of course, they aren't flowering plants either. And, to add to the confusion, at the top of the tree, there're are several new spring-green leaves, although the lower leaves seem to be suffering. Help!!! I got it for my birthday, and it wasn't particularly cheap, so I'd really like to save it somehow but can't find much info on the web or anywhere. Thanks for answering my question.

Why are the leaves on my Acacia Dealbata falling off?
Acacia dealbata (silver wattle). Florests sometimes market and refer to it as Mimosa.

Good description given at:

http://en.wikipedia.org/wiki/Acacia

and

http://plants.usda.gov/java/profile?symb...



I realize that you understand that the Delabata is not a good indoor plant simply because its light requirements are too high for anything other than a bright greenhouse and a bright, like day, light supply of several hours per day. Its mimimum light and hours of expousure to just keep it alive is still too high for indoor situations. I believe, as you well suspect, that insufficient light is the cause of the (defoilation?) ". . . lower leaves seem to be suffering," you see. It's trying to live as evidence of new leaf initiation, but its energy reserves are being used up and it can not sustain the drain for very long.



I realize that you are under a garden temp constraint for this plant. Perhaps you have the wrong plant for your garden since the grower's cultural instructions/conditions indicate a minimum tollerable temp of 4 C. So, what is going to change after this summer and your Dealbata is out there this coming winter?



To give you an idea of how much light this plant needs; use a camera having a light meter that will indicate the f-stop being used for exposure of 200 ASA film with a shutter speed of 1/125th second. Out doors, focus on a sheet of typing paper, filling the view finder with an image of the paper; with the paper positioned to get the full blast of the sun. This would be 10,000 to 12,000 foot candles at noon, which the Dealbata likes and an f-stop reading on your camera way up in range of f-22 to f-45 depending upon the lens attached.

Then indoors, same paper, same camera; position the paper in the brightest, lighted place you could place the Dealbata. What is the f-stop? Way down? Even the strongest light requirement, indoor plants need f-11 to 16, which should be in the vacinity of a window receiving direct sunlight. At windows not receiving direct sunlight will read around f-8 (good for spider plants and Dieffenbachia). If the reading is around f5.6, this is good for the lowest light requirement house plants. And all of the above for several hours daily, not just 2 or 3 hours.