I have this s#!t in one of my training pots every year!
It drives me crazy because it grows across the soil surface fast and is impermeable to water.
The root system is deep, so scraping takes about 10mm of the top layer of soil with it, which needs to be replaced.
I scrape it out repeatedly over the warmer months, only for it to grow back - FAST.
Then, at repotting time, I wash and flush the roots to rid the soil of it.
Come spring, another random pot will grow this stuff.
It only occurs if the tree has been left in partial shade - where the soil remains a bit on the damp side.
No idea what it is, but keep picking it out because water won't get through the foot print of this stuff, and it can leave the under-soil dry even after drenching!
