Avocado leaves with yellowish/brown spots

Question

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?

Answer 1

Not an expert, but it looks like possible iron deficencies. There are macro-nutrients, that we all know of N,P,K... the regular stuff we see in fertilizer and then there are micro-nutrients. The two micro-nutrients that tend to be most often deficient in potted citrus plants are iron and manganese, especially iron. Iron effects the new growth the most. You should spray your leaves with a watered-down vitamin mixture. You can also add the correct amount to the soil, if your plant it is in it's growth season, but do not add it to the soil during their dormant season.