Moss will grow on all kinds of surfaces in shady and moist conditions, but it requires an acidic growing medium. An easy way to acidify the surface of terra-cotta or stone planters so they look aged with mossy exteriors is to paint the pots with yoghurt. Yoghurt culture is acidic enough to support moss. Applying a moss smoothie is a fun project you can do with the kids to beautify a patio or garden.
Collect moss from your garden or neighbourhood, or buy moss spores from a gardening centre. Clean most of the dirt from collected moss, and allow it to dry to the point that it easily crumbles.
Place the pots and saucers on a paper-covered bench or porch.
Add one part dried, crumbled moss or moss spores to four parts yoghurt in a bowl. For example, for 612 g (2 1/2 cups) of smoothie, use 122 g (1/2 cup) of moss and 490 g (2 cups) of yoghurt. Mix the moss and yoghurt until it is well blended.
Paint the moss smoothie onto the exterior of the pots and the rims of the saucers. Do not paint vertically; move the brush around on the pots, so the moss will not form unnatural stripes on your planters.
Place the painted containers inside plastic bags, and set them in the shade or in a cool garage or potting shed where they are out of direct sunlight.
Check after a few days to make sure the containers are not drying out. In 10 days or so, the pots should be covered with a light film of moss.
Use moss-covered pots for plants that get watered frequently. As long as the pots don't dry out, the moss will continue to grow on them. Moss yoghurt paste works on all porous stone, clay, and organic surfaces, so use the moss-growing technique to age fountains, garden statues, shady sections of garden wall, decorative boulders or fallen logs.