Jamieson, Fausset and Brown on 2 Samuel 23:4

4. as the tender grass springing out of the earth by clear shining after rain--Little patches of grass are seen rapidly springing up in Palestine after rain; and even where the ground has been long parched and bare, within a few days or hours after the enriching showers begin to fall, the face of the earth is so renewed that it is covered over with a pure fresh mantle of green.