The leaves turning black is also a good indication of root rot. Even if the soil near the top of the pot feels like it needs water, the soil down inside the pot may still be wet. So, we often think they need water when they really don’t.

If this were my plant, I’d take it out of the pot and examine the roots. If there was any mushy, rotted roots, I’d remove as many of them as I could. If there were a lot of decayed roots, I’d actually remove them and let the plant sit out of the dirt for a couple of hours so the roots can dry a bit. You wouldn’t want to do this in the hot sun, but inside your house or a garage would be fine.

If the roots are rotting and this is the problem, I would re-pot the plant making sure that the pot had a hole for drainage. If you just don’t want to repot right now, you could stick your finger into the soil as far as you can to see if the center near the roots is soaking wet. If it is I’d definitely repot the plant making sure the pot had a hole in the bottom for excess water to drain out of.