One of the great experiences of my life was learning bryology from Dr.
Howard Crum of the University of Michigan. One day when our class was
in the field with him, I somehow broke his glasses. You'd think that
would end the field trip, but Dr. Crum knew mosses so well that he
could tell one species from another just from the color and where it
was growing.

Which is a long way of saying: there are thousands of species of
mosses, and they have different moisture requirements. Some grow in
very dry, hot environments (on rocks or tree trunks) and others need
quite soggy habitats (some only grow in streams). There are only two
mosses commonly seen in bonsai pots (unless someone introduces one
intentionally): Bryum argentium, the "sidewalk moss" and Funaria
hygrometrica. Both of these favor dryish (for a moss) disturbed
environments; Funaria is one of the first mosses to come back after a
forest fire. But dryish for Funaria may be too wet for a conifer.
Bryum can be identified by its silvery-grey color; it gets its common
name because it likes to grow in sidewalk cracks (and on roofs). I
don't worry about over-wetness when I see either of these in my outdoor
pots (I would if they were in my indoor pots); I worry that they impede
drainage; instead of roots they have fine filaments that clog up soil
pores. I always pull out most of a moss colony, and leave a few
clumps.

Nina.

Can I tell another Dr. Crum story? Once he was driving and saw what
looked like interesting lichens on a tree in someone's yard. So he
pulled over, pulled out his hand-lens, and began to examine the lichen
at eye-level. A passing car slowed, then the driver yelled "IT'S A
TREE!"

chris wrote:

So should I remove the moss? or just leave it? the moss hadn't been
growing until I started fertilizing.