Sagina subulata as moss substitute

Sagina, called ‘pearlworts’ or ‘Irish-Moss’ (Dutch ‘Vetmuur’) can very well serve as a substitute for moss in a Japanese garden. Unfortunately we have a bad experience with it.

In my post ‘Groundcover maintenance’ I wrote about the fact that Sagina is one of our most feared and persistent weeds in the ground-covers, or actually every ground surface.
How can that be ?

Note:  Part of the season this ground-cover will be covered with small but prominent white flowers. If you do not like that look for an other moss substitute.

We have had Sagina before in a previous garden and it performed great. When we started our Tsubo-en project one of the moss substitutes that we wanted to use at the time was Sagina subilata cultivar ‘Aurea’ . Compact and dense growing with relatively short stems and purely white flowers.
At least that was the intention. We where sold the wrong species !
It proved to be Sagina xxx-something. Not the cultivar that we had been looking for but an other species that multiplies via seeds. Very potent seeds.
By the time we found out, a couple of months later, it was already too late. Although we tried to removed all of it at the time, the harm was already done and seeds where spread. From then on we have been and are still spending a substantial amount of time to limit further spreading. Something that is impossible. On the other hand we can not just let it go because it will even populate end for sure eventually overgrow, the Ginshanada.

Related: Mosses and lichen, Unwanted mosses.