Answer: Moss usually grows in moist, acid soil in heavy shade, or where soil is otherwise not in an ideal condition. This might mean it is also compacted, low in fertility or low in organic matter. Rather than adding topsoil, I would suggest working in a hefty amount of organic matter such as compost to help repair the soil structure. Lime will help to correct an overly-acid soil, however you should perform a soil test to determine how much lime to add. If you plan to grow grass lawn in that spot, the soil test can also provide recommendations for proper fertility. I should caution you, though, that lawn does not usually grow well in deep shade where it faces heavy competition from the trees for light, moisture and nutrients. You might also consider some form of a groundcover.
Q&A Library Searching Tips