Best answer. This person's right on the money.Just water thoroughly, until the soil is saturated, you can water over the course of a couple hours if you wish but eventually you should get some drainage (run-off) coming out of the holes in the bottom of the pot(s). You can tell it is time to water when the containers have lightened up considerably (lift them if you have to), and the soil is visibly drier (not completely dry).
Larger containers are typically watered less frequently.