It sounds like you got one of those premade so called bonsais. Once you bring them home dont repot it for about 2 weeks, so that it can become housebroken:) Ficus are pretty tollerable of dry soil, I would water it once a week at this point. Usually these trees have poor root systems, and hence dont drink as heavily as established bonsai. Does yours have glued on gravel?, if so remove it so you will be able to monitor soil moisture. You want the soil to become dry to touch between waterings, if its moist or damp, then dont give it water. In terms of the rot, I would carve out that portion to prevent it from spreading. You may want to mix up some new soil that is more pourous and drains better, because those wal mart bonsais are potted/packeged in a way(heavy soil) that will maintain moisture for long periods during shipping etc., which will lead to rot, but they dont care, because the plants are usually purchased before this happens. Im not sure what your intrest level in bonsai is, and Im not sure if you care about traditional styles, but I have personally never seen a bonsai come out of walmart that has a shape that even remotely resembles a tree at all. They are often root cuttings stacked together that have produced shoots. The wide spaces between the roots make any transformation into a convincing tree shape next to impossible. Yet from walmart, for even less money, you can find large 1gallon houseplants (especially the benjamin ficus), that can easily be converted into an atractive tree-like shape over a couple of years, by mearly pinching the ends of the branches anually (yet producing a show quality bonsai will require much more devotion and information), If this is what your looking for. good luck, and oh yeah, often those bonsais at walmart are made out of species that are popular for bonsai, so I have been known to buy these ugly plants for 2 reasons. 1-they are often cheaper and larger than the same species can be found anywhere on the internet. 2- even if they are ugly, I buy them just to remove branches or the tops off of them, to propagate these, because they still have potential because they havent been mucked around with yet, although if you like the way it looks already (whether "properly" shaped or not, and the plant makes you happy then great, thats the whole reason any of us start this hobby anyway.
take care,
castorcrap

castorcrap - thanks so much for the advice. Honestly I thought they were "cute" and something interesting for the doctor's office I work at. The patients love all the plants. I just got in some new bonsai pots that I ordered b/c I truly hate the glued stone thing in the ugly pots - grrrr! I have correct soil for them as well. I just hope I don't kill it while "carving" out the mush...poor thing...it'll need plast surgery by the time I'm done. Is there anything I should watch for or apply to the "wound" when I'm done?

yes, they make a cut paste that you can apply to seal the wound. Im sure there is somesort of homemade concoction out there that you could mix up, I think Ive read about using modeling clay w/ a little bit of olive oil added to it. I know before I bought cut paste, I used one of those tubes of rose prunning sticky paste, I have even used a very hot knife to cauterize it to prevent any sap bleeding.

You can use ashes for sealing ficus wounds.

how do i know when my ficus has root rot?

The best way to seal a wound other than using Bonsai cut paste (which is mainly meant to keep out any bacteria) is to use Vaseline (introduced to me by a respected very old friend and Bonsai artist). This will keep a good barrier on the wound and help it heal properly. I in fact use this on almost all of my trees except for my prized/more finished show pieces or ones with special needs or prone to die back, in which case I use Japanese cutpaste.

Ficus (which has over 2,000 sub-species) is a very forgiving Bonsai subject copes well with too much or too little watering (respectively) and can survive well in low lit environments and in my opinion is the best beginners Bonsai. I have three types of ficus myself and would say the best soil mixture for them (and most other tropicals) comprise of equal parts:

Turface MPV (can be substituted for lava rock)-- (Porous)
Haydite (can be substituted with shale or grit)-(Non-porous)
Fir Bark (can be substituted with Pine bark)-- (Organic)

The best way to tell when to water is to stick the tip of your finger in the soil about an inch or two near the edge of the pot. If the soil feels almost completely dry with only the slightest sign of moisture its time to water. A beginners method for this is to stick a chopstick in the soil. When you pull out the chopstick and its dry, its time to water.

Adeeb, root rot is pretty obvious. The tree will begin to show signs of deterioration (dropping of leaves, branch die-back etc..). The two main causing factors of root rot is over watering and or over fertilization (which will burn up the roots). If root rot is apparent it is required to do an emergency repot, removing all affected roots. Using the method given above you should be able to water efficiently.

-Good luck

-Mike

Didn't realize this post was so old. Could have cut my reply a lot shorter :)