When using scotts miracle grow moisture control soil, when and how much water should I use ?

Japanese maple is 1 1/2 ft tall,Thai pepper is 1 ft tall. Both in 3 gallon pots. All indoor plants. Help! They are starting to wilt and I don't know if I'm under or over watering them. I don't use plant food as MG already has nutes. Hoping to transfer maple outside when I move to new house in 4 months.