I grow several different Aralias and I can tell you that it is very important to keep the plant warm, especially in winter. 65F(18C) is the cut off: below that it will stop absorbing water and then you should water it less, allowing top 2-3" to dryout, otherwise the root-rot is certain. by the way most of the roots of Aralias are at the bottom of the pot, even on mature old plants. you can poke around with a spoon to see if top soil has any roots or not.
in winter in cold climates the area near windows gets much colder then the rest of the room. So you get a dilemma: this plant needs partial sun at all times, but getting partial sun at a cold window is not a plus. It's better to keep near the lamp or overhead lighting of some sort but away from windows in a warmer part of the room.
It also needs high humidity. if it's less then 30% RH the plant will suffer and drop the leaves.
Unfortunately it is not an easy plant to grow if you do not provide the conditions it likes. I fully tent my Aralias in large plastic bags for 3 months of winter positioning them within 2 feet(60cm) from western window which provides sev hours of warm light. keeping it in plastic gives it higher humidity and keeps it warmer.
but even with such tender care my Aralias drop some leaves in winter.
the optimum conditions for growth are : humidity above 75%, temp in the 80s (30C) and plenty of water. at high temps they absorb much more water and start growing leaves like crazy. To get that I put them outside in aug, when night temps do not fall below 75F(24C).
