Hello, I have a huge problem with my mandarin tree, it's dying. And I don't know what to do. I've tried to replant to new soil with 2-3 cm rock layer for drainage, after that I fertilized, I sprayed the boron preparation and watered it after 2 weeks. But nothing worked. Still my tree is dying and I don't know how to save it. Now is winter and on windowsill (there they placed) is around 18 degrees.
Mandarines do like sandy soil. They don't tolerate constant wetting roots. Your soil is weird. Very rich of salts. Possibly it's too dry air and you water the pot too often. It is not good idea to keep your container in a high edged water collector. Your container is not high enough and high edged water collector keeps its lowest quarter wet for long period. Leaves are also like there is an infection of some kind. You may try: 1. deeper container 2. better drainage, better soil aeration - use sandier soil, don't use high edged water collector under the container. 3. water more seldom and maybe by lesser quantities at once 4. spray leaves regularily, if the air in the room is very dry.
I keep my mandarines of that age in a (empty) 60L aquarium in winter time to keep their humidity higher than in the room. You may use a large glass jar upside down on top of each of your mandarine container, but be sure first, that the soil is not too wet. I use aquarium light to supplement scarce winter sun. But I am several hundreds kilometers north of you and I have only narrowly 6 hours of daylight here now.
PS sorry for english mistakes :) This is very good idea, maybe I try to find something similar to aquarium.
