Q: I plan to plant Scotch moss between the stones in my patio. What kind of soil preparation should I do?
A: Scotch Moss (sometimes called Irish moss), Sagina subulata, isn’t really a moss but it has the green, low-growing, tufted texture of true moss. In my experience it will not do well in full sunshine; semi-shade works best, particularly in the heat of summer.
Typical of most plants, Scotch moss like moist but well-drained soil. My advice is to excavate six inches deep between the stones and fill the cracks with a high-quality outdoor planting soil. This soil mixture is different from potting soil, which holds too much moisture.
You can split by hand the root balls of Scotch moss bought at a nursery and plant each piece four inches apart in the cracks between your patio stones.
The biggest enemies of Scotch moss are dry soil, soggy soil and high humidity. Be very attentive to watering in summer: do it in the morning so the foliage dries before nightfall.
If Scotch moss doesn’t thrive, try super-dwarf mondo grass, Ophiopogon japonicus ‘Nana’. If you have more sunshine than either of these plants tolerates, experiment with creeping thyme, Thymus serpyllum.