Boy, does watering depend on so many things! Can't deny that what Zoe and Tiffany say are right! I would like to add that the ambient level of humidity in the air also has an effect on when to water. I've noticed my watering is less on days in the 90s when the relative humidity is 50% or above. The drier the air gets in the summertime, the more frequentlyI water. The type of soil also plays a big role here. Almost all potting soils sold are essentially "soilless"; they don't have any actual dirt in them, just ingredients such as peat, vermiculite, shredded wood chips, etc. Some are designed to be moisture retentive, they say so right on the package. Other mixes are made for cacti and succulents, which need a fast draining mix. You need to consider the water requirements of any particular plant and use the right potting soil mix when you plant it.
