My Ming was purchased from a reputable garden center about a year and a half ago. Yes its was summer at the time. I live in SE Wisconsin. I mist her and am constantly checking her water demands. She has always be in a South facing window out of direct sunlight and doing well. Recently I moved her to a different room with same exposure, but she has been dropping her fragile fern-like leaves for over three weeks. She is looking pretty sparse. I was wondering if the soil acidity level could be a reason for this. I put earthworm castings into the soil to keep it fresh and fertile. Do you have any other ideas?
Ming Aralias do not like change and react strongly by suddenly dropping many leaves when they are relocated, their watering changes or they are exposed to temperature changes. I cannot say just which of these apply to your Ming, but I will explore some possibilities.
If the light is identical in its new location, then that would not be a problem. However, even though the south exposure is the same, it does not mean the light the Ming receives is the same. The size of the window, the distance from the window, the position relative to the window, the coverings on the window and even what is outside the window (trees, buildings, etc.) can all affect how much light a plant receives. You haven’t provided details, but my educated guess is that the change in light is what your Ming is reacting to.
A single lapse in watering can be followed by a flush of yellow leaves, so that might be a cause. BTW, misting provides no significant benefit to your Ming so it is important not to rely on that at the expense of proper watering.
If the temperature, especially at night, is lower in the new location, that may be causing the leaf drop.
You didn’t mention repotting, so I assume that is not an issue. However, disturbing the roots will usually cause substantial leaf drop. Mings rarely if ever require repotting.
Soil pH would be a problem only if your local tap water is on the hard side. If so, use filtered or distilled water. It is unlikely that the worm castings have substantially altered the soil pH, but they are also providing little benefit, so I suggest that you stop using them.
I hope this has given you some things to focus on regarding your Ming leaf drop. Once you determine the cause and correct it, you should see gradual lessening of the leaf drop.