Cobbles and pebbles are stones which are smaller than boulders and larger than gravels (usually in the range 60-250 mm in diameter). As used in garden design, cobbles are water-washed, by rivers or the sea, and therefore rounded. Flint and granite form excellent cobble stones. Sea washed cobbles and river washed pebbles are che choicest. Cheap aggregates are less desirbale.
Many plants are very happy to grow in cobbles and pebbles. They conserve moisture and reduce competition from weeds, which also find it more difficult to germinate beneath cobbles. This arrangement is known to Alpine gardeners as a scree garden. It keeps the roots moist and the leaves free of standing water.
Cobbles with stepping stones
Cobbles with Euphorbia