When instructions for a plant state to "keep the root ball moist," such as for a Boston Fern, how often would the plant likely need watering - would it ever need watering every single day?

How does one check whether the root ball is moist?

Just because the soil at the surface is dry does not mean the root ball is dry too, right? I stick a finger in the soil about two or three inches to check. Can someone please confirm how to water a plant with directions to keep the root ball moist?