A variation of the basic watering method makes plant care almost automatic, allowing you to leave plants unattended for several days at a time.  Place a container (such as a glass jug, available from wine-maker supply stores, or an old thermos jug with spigot at the bottom) of nutrient solution above the plant container's soil level, and connect tubing so liquid can be either gravity-fed or siphoned.  A clamp (such as those available from sickroom supply stores and some hardware or automotive equipment stores) attached to the tubing will regulate the flow; this way just the right amount of solution goes through.  Be sure to set the planter on a tray or something similar to catch drips.