It depends on the plant. Some, like fuschias, really like water, and you should water twice a day. Others are more drought tolerant and don't need watering much at all. Let the plant tell you-- if you're watering once a day and the plant seems to be doing ok, then you're fine. If it's drooping later in the day, then try watering later in the evening, around 4-6 pm. If that still doesn't work, then you probably should water twice a day.
You can also buy soda bottle "tips" for continuous watering as needed. It's an attachment for your 2 liter bottle that you put on. You fill the bottle, stick the tip on, and insert into the dirt next to the plant. As the soil dries, the water is drawn out of the bottle.
at 9:28 PM on May. 26, 2009