ser,

Your soil type and amount of organics are most important in determining when to water. Since you are doing the soil moisture observation method, check a few inches below the surface of the soil and not just under the mulch. Some people use a stick or chopstick to check further in the soil. You don't need to water until the soil, at the root zone, is slightly moist to not completely dry. It is not an exact condition. This will happen faster in sandy soil with good drainage. It will take longer for clay soils with poor drainage. It will happen faster in soil with low organics and slower in soil with high organics. You can find out what you have buy sending a soil sample to a horticultural lab for analysis. Also, certain plants like different conditions and watering regimes. Check the other plant forums. Water and wait till the plants show a slight sign of stress(drooping)and that is the time between watering the present conditions. It will be different in hot versus cold weather conditions and overcast versus sunny conditions. Aloha