So I just came home for christmas and the avocado plant I left under my mum's care is not looking good. Old leaves and some of the new are drying and falling off easily. I know she's been watering the plant every few days, waiting for soil to dry between watering and generally caring for it just like I did before I left. It deteriorated from a healthy looking plant to this in about 2 months. I don't remember how old it is exactly, but I've grown it from a pit and it's over a metre tall now. It's been re-potted once, about 4 months ago. I'm not sure what else can I say, I'm really dumb when it comes to plants, and that's why I'm here. Can you help me save my son? I'm attaching photos of how it looks now, as well as 5 months ago. (cacti in the background will be repotted soon)
I know it's been 4 months since the question was posted, but... Because it was December, and I see that your plant may have been sitting next to a heater, I would suggest taking it out from the flat during the winter. The humidity is probably quite low with central heating and the plant also needs to rest in little lower temperature during the winter season. I saved my 2 avocado plants by quickly moving them out of the flat to the staircase where there is 12-15 Celsius Degrees. They were starting to lose leaves just like your plant did and this one trick saved them both. You just have to find a spot with fair amount of daylight and proper temperature.
If that's not the case, then maybe it need a soil that is more loose. You may add some claydite to prevent the root rot.