We inherited a flagstone patio when we bought our house last year. It is in a shady area right next to the house. The spaces between the flagstones are quite large--a couple of inches in many places--and are filled with compacted clay soil. They basically just get muddy and grow weeds. Because it's so shady (an hour or less of sun per day, and we have a table and chairs on the patio creating more shade), I haven't found any great ideas for groundcover/moss to grow. I did experiment with some irish moss last year, which is still alive, but it hasn't spread much and unless it starts spreading more quickly, I probably can't afford to buy enough to fill in all the spaces. So: any advice about what I should use to fill those spaces? Some kind of moss or groundcover? Pebbles? Stone dust?