Kusamono are the small plantings of grasses, wildflowers and herbs grown and displayed in their own right, often alongside bonsai to set a season and a mood. Moss is their usual finishing ground, the green skin that ties the planting to its pot and makes it look settled and complete.
What kusamono are
The word means "grass thing", and that captures the spirit: humble, seasonal plants rather than grand specimens, arranged to evoke a particular time of year or kind of place, a damp meadow, an autumn bank, a patch of spring woodland. Shown beside a bonsai they provide context and contrast; shown alone they are a quiet art of their own. The closely related accent plantings used specifically to complement a bonsai display are sometimes called shitakusa.
The place of moss
Moss does for a kusamono what it does for a bonsai: it covers the soil, keeps it cool and damp, stops it washing out, and finishes the composition with a natural, aged look. Beyond the practical, it belongs to the aesthetic, suggesting the mossy ground these little plants would grow on in the wild. A fine, flat carpet moss over the surface, with the chosen plants rising from it, is the typical treatment.
Plants and pots
Choose modest, seasonal material: ferns, sedges, grasses, small wildflowers, miniature hostas, anything that reads as a scrap of wild ground rather than a showy garden plant. The pot matters as much as the planting, usually a small, understated, often handmade ceramic or a simple slab, chosen to suit the plant and the season rather than to dominate. Restraint is the whole point.
Care
These are small, shallow plantings, so they dry quickly and want regular watering and a position out of harsh sun, much like the moss that dresses them. Many are treated as seasonal, brought to their best for a display when their plant is at its peak and rested afterwards. Keep the moss damp with rainwater, clear debris, and divide or replant as the material grows, and a kusamono can be kept and refined for years. The moss side of it follows the same principles as moss for bonsai.