Heptapleurum sparse and dropping leaves
Hi, my mom divided a heptapleurum about a year ago into two pots. They were growing well and had nice full umbrellas. My mom had kept them outdoors but said they'd be fine indoors. The branches were quite knobby and unruly-looking, but I thought it looked nice and they were mostly hidden by foliage.
I put one in each room (bedroom and living room). Both started dropping leaves, at different rates, and pretty soon had nothing left except a bunch of knobby branches, that were the gray bark color, not green. I sent the worse-off one to my upstairs neighbor whose sunroom was empty. That one grew back most of its leaves and started to look healthy. Meanwhile the one in my living room stayed sparse.
I then moved them both into my own sunroom, since my neighbor's had success, where teeny heads started to form again. They keep growing to the size of say a nickel to a quarter, and then leaves start falling. The plant always has a little foliage, but if I so much as brush past the plant, leaves fall. This has been going on for 5 months now.
The soil is probably questionable, it gets really hard when it's dry, like a solid cake. I don't know where it came from. Every room in my apartment is dry, and everything is near a radiator. I have ordered a humidifier so perhaps that will help. But the draft can't be avoided. The sun room is south facing, but on the first floor and naturally partly shaded by the trees outside. All of these conditions are pretty similar to upstairs, where it seemed to do ok.
When I water it, I usually wait for the pot to dry out, then water it again until saturated.
Any thoughts on what I can do to get some rich foliage back? I've posted a photo in the link here. Thank you for any insight you might have!
Here is a link that might be useful: