Q: I plan to plant Irish moss between the stones in my patio. What kind of soil preparation should I do?
A: Scotch 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. 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.