I'm worried about the potting. I wonder if the soil is retaining too much water. Schefflera's don't need much light, but north east is not an ideal angle for a window either.

I'm confused by the fact that it looked so healthy and then deteriorated so drastically within a week or so. If the soil is the issue would you expect the plant to have done so well for almost 9 months? Could this be a sign of root rot? Here are more recent photos:

Could be wrong, certainly. Just my guess by the looks. I've definitely purchased plants that were due for a re pot, and were in poor soil that dried fast enough in summer sun, but you keep it in a dim room where it barely dries and remains root bound, and while it seems to go downhill suddenly, it's been a problem waiting to show. Let's see what others think!

I took the moss and stones off from atop the soil, and gently removed some of the soil from the edges of the pot. The soil was still wet all the way through despite having been watered 4-5 days ago. The smell was reminiscent of a garden after consecutive days of rain (slighly boggy... liike decomposition). I've left him that way to aid in evaporation, and I'm thinking I'll repot him in a lighter soil.

I have mine in gritty mix, but soil with a lot of perlite could work. When I've had plants with this sort of stress (most often orchids), I removed dead and rotten roots, washed with hydrogen peroxide, and then repotted.

Do you recommend removing the blacked leaves and branches? Most of the branches have some black patches. The bark's texture has changed- it now looks wrinkled and deflated.

Hmm, I'd be interested in other opinions. While you don't want to add to the stress of the plant by trimming, I think those 3 branches are probably too far gone - if it were my plant, I'd remove those blackened parts to avoid any infection spreading. The plant may be too far gone at this point - the choice might be moot or 6 and a half dozen.

When I buy a plant, unless it has flowers, I almost always re-pot immediately because you just don't always know whats happening below the soil until its too late.

5 days ago I removed the dead braches, repotted the tree, and put it in a bright easterly window. The few braches that were left have since blackened, the bark has hardened and lightened in color, and I'm noticing little holes/indents at the branching points. Any idea what these are? What is the last-ditch effort recommend for these situations? Can I gain any additional information by inspecting the roots? Is it advisable to wash the roots or cut back the trunk?

While those days are long behind me, I have killed a few scheffleras in my time. It looks like this one may be too far gone, guessing from the photos seeming to show that the trunk is also shriveling, not just the branches. Last ditch effort would be completely unpotting, rinsing roots free of soil, trimming roots AND stem back to clean healthy tissue with a clean blade, and seeing if it buds. You'll probably have a little stump compared to what you started with, but this species is resilient and sometimes will sprout leaves from a stump. You might find that whatever is eating away at your plant (probably fungus?) Is throughout all tissue and it can't be saved. Crossing my fingers for you!