The cambium is alive, I had to cut off some of the top branches few days ago with no leaves on it, and they were all alive.
Unfortunately I live in London, United Kingdom so no coast here I'm afraid :-/
Is this vinegar or H2O2 brushing is not dangerous for the trunk? Should I dilute it before I use it or not?
Thanks.
Norbert

Your tree looks like it may be okay; but you definitely still have issue. First thing is if the soil is below 60 F, the roots will not grow; and if the roots don't grow, the plant won't grow. Maybe you could put some sort of heating pad under the pot. Next is the pot itself; clay pots (terracotta) evaporate water through the pot, which cools the soil; and citrus roots do not like to grow into cool soil. Your tree is a Meyer; so it is very sensitive to changing light conditions; it will drop many/most/all of its leaves to later replace them with new leaves better suited to the new light. If you treat it well, it should recover. If you over water it, it will drop leaves; if you let it get too dry, and then water it; it will drop leaves. Cow manure is a very good fertilizer for Meyers when they are planted in the ground; I am not sure about in containers; you may get a salt buildup. Most container growers on this site are big fans of Foliage Pro. Welcome to the Meyer lemon family; and good luck.

#johnmerr thank you very much for your advices too.
Yes, I already got a heating mat which I have placed under the pot.
It supposed to heat up the soil 10-20 F above ambient air temperature, hopefully this will increase the root growth. At the moment my Meyer tree is in a tent, gets 12-14 hrs light and during these hours it gets around 75 F, 45-50% humidity and little air ventilation trough the hole on the side of the tent.
When I re-potted the lemon, I placed the cow manure at the very bottom part of the soil mixed up with a bit of soil, than I had one layer of mixed soil on that and than I put the lemon tree on that as I was advised to make sure that the root won't touch the manure directly.
Thanks again for the help and the warm welcome, all the little help and suggestions means a lot to me as I really would like to save this tree as it has proved to be such a little warrior :)
Norbert

Use the vinegar or H2O2 as it is in the container. Alcohol should be diluted 50% water. You'll use just enough to wet the trunk every other day for 4 days then see how things progress.

Norbert,

You are putting a lot of energy and resources into your tree; let's hope it responds positively. When grown in containers, Meyer lemons have a deserved reputation of being "finicky" (not my word, which is why the quotes); but the rewards are great. My company's motto is "If life gives you lemons, pray they are Meyers".

#poncirusguy
Should I dilute the vinegar before I use it?
I have heard that a little bit of vinegar + water mixture would decrease the pH and prevent salt build-up on roots, but what will happen if I brush a little bit on the trunk and why is it beneficial? Does it have something to do with fungus infection?
Sorry, I'm curious before I try it because I never heard this before.

#johnmerr(11)
Thank you, yeah, it's been a lot of energy so I do hope that our tree will be thriving soon. :D