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.