Before we talk about getting water to your roses, we first have to talk about what happens to water in the soil. Depending on the makeup of your soil, these pores are a mix of large spaces that fill and empty with water or air fairly readily by gravity, and smaller pores which take up water by capillary action. You may have seen capillary action if you have had a finger-prick blood test, such as when you donate blood. After your finger is pricked, a drop of blood is squeezed out and a thin glass tube is placed in the drop. 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.