Does Golden Scotch moss spread very much? Is there a way to help it spread laterally quickly?
Scotch moss, along with its close relative Irish moss, are both medium spreaders. By planting them closer together, you may be able to fill in the area quicker. Though its focus is on the Irish variety, this article will help with growing either type: https://www.gardeningknowhow.com/ornamental/groundcover/irish-moss/growing-irish-moss-plants.htm
How far down do I have to dig when I’m removing it? Should I remove the sonfar healthy looking periphery? Do I need to remove all the soil and replace it with new or treat the soil with fungicide? When can I safely put new moss in that space? Denise
It should pull up in mats somewhat easily. I would only cut and remove infected areas, and treat with the fungicide of your choice.
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
Make sure that the soil does not remain soggy in this area. They will not tolerate soggy soils. Allow the area to dry a little in between waterings.
https://www.gardeningknowhow.com/ornamental/groundcover/irish-moss/growing-irish-moss-plants.htm