TLDR: Citrus keeps turning black and oozing resin. But I can't find the problem. I thought it must be root rot, but they look perfectly healthy:

Long version:
Because my first and second citrus trees fell victim to root rot, I started using a very airy substrate made of pine bark, perlite and some humus/worm castings in a 5:1:1 ratio for all my plants (figs, pineapple, cherimoya, monstera, etc.) with little adjustment. You may recognize this as 'aroid mix'. But it works surprisingly well in my indoor space with a west-facing window and terracotta planters (and my tendency to overwater).
But I can't wrap my head around citrus.
It always starts with rapid growth, followed by very suddenly dropping and crisping leaves, black stems and finally death.
I thought I must be root rot again, which I need to mind during winter. But today, when I dumped my fifth (!) tree, I found only perfectly healthy roots and nice smelling substrate.
I think it must be a pathogen… but what?
I am at a loss. I keep killing my citrus trees and I don't know why. :'(
EDIT: replaced "5:1:1 mix" with "5:1:1 ratio" for clearification.
Weder Bokeh noch eine hübsche Farbpalette sind Garant für ein KI-Bild.
Ich hatte so ein Kommentar auch neulich unter einem Scheißepfosten von mir. Und obwohl es ein Scheißepfosten(!) war hat's mich minimal traurig gemacht, dass so ein Kommentar kam. Vorallem, weil ich beim fotografieren die Kamera vor leisem glucksen kaum still gehalten bekommen hab.