I have two young avocado plants in my room that show some problems.
The older one (I started growing the plant from seed 4 months ago) started to show yellowish/brown spots on its leaves about a month ago and is losing these leaves quickly after the spots appear.
The second one I started growing about 3 months ago. It doesn't have these spots but started to grow misshapen leaves and lost some lower leaves as well.
It's summer where I live (Switzerland), so it should be warm enough and they sit next to a bright, southeast facing window. I water them when the top inches of the soil are dry. I also tried to spray their leaves because I thought the air humidity might be too low, but that didn't help either. 4 days ago I then tried to add very little fertiliser to the older plant, but haven't seen any changes to the better either.
Do you know what could cause this?