The blood magically races up the tube. Capillary action is the reason water in a saucer is sucked up into a flower pot. In a soil with mostly large pores, water travels through quickly, and the small pores don t have time to suck up water before it s gone. In a soil with mostly small pores, the water runs off the surface, and the small pores never get contact with the water. Organic matter has a combination of large and small pores, very much like a sponge, but the material itself has water-holding capacity, where the mineral particles of soil do not.
Organic matter helps slow down the water passing through so the capillary pores can suck it up.
Since few of us have the first ideal soil to begin with, we usually have to make our own combination of the second. When water hits the soil, gravity takes over. The water rapidly fills the large pores, and the smaller pores fill more slowly. If the water continues to flow, eventually the soil fills completely and reaches saturation. If the soil stays this way, the roots will drown.