The rule of thumb is to follow the label directions! Depending on how you diluted up your MG, it generally recommends use every 7 - 14 days. It is true that continual watering will leach it out faster, but if you note on the box, it usually gives a recommendation for how to dilute if you would prefer to fertilize at each watering.

If anything, less is more for the artificial fertilizers unless you ensure you are able to flush the soil with plain water on a regular schedule. If your plants are happy, then let them be. I have gradually moved to the slow-release fertilizers so I don't have to manually fertilize as often.

It completely depends on how often you are watering and how much water you allow to run out of the bottom of the container. Right now, with temperatures at 90/70, I find that my mature plants with lots of foliage require more than the smaller plants. Evaporation rates have hit the top of the scale. I water (about an inch" every day and a half to two days. I feed MG (for tomatoes) about every 10 days.

I did look on the box. It said, 2-3 weeks after planting the tomatoes in Miracle-Gro soil, start feeding regularly with Miracle-Gro Tomato Food.

"Regularly" is...once a month? Twice a week? Not much help.

I feed mine about once a month, I use MG tomato food. I have nine plants, only six have tomatoes so far.