Well, for a 1 gallon pot I usually let them have about 1/4 gallon ( 4 cups ). Just pay attention to your run off, water slowly to let your soil soak it up well and when you start to see run off building up your good.How much you water once at a time, isn't as crucial as how often you do it, if that makes sense. You can give your girls a good soak, just make sure that the roots are absorbing most of that before you go dumping more in. Otherwise your soil will turn to muck and your roots will have trouble getting oxygen, and thats just the tip of the iceberg. The absolute best way to know when to water is to simply pick up your pot. Get familiar with what your pots feel like when their dry, so all you have to do is pick them up and you'll be able to feel if their still retaining water. Hope this helps.