What's the best fertilizer for potted cherry tomatoes?

You can use compost, worm casting as long as it is mixed into your potting soil. You don't want to grow leaves but fruit. You will need to learn how to prune your tomato plant. Here is a diagram that shows how to prune your plant.

Compost or worm castings mixed with potting soil.

Fertilizer higher in potassium

There are many fertilizers out there for tomatoes. If you get confused as to what to get, just ask someone from a garden center which would be best and make sure you tell them the tomato is potted and not in the ground. They may ask what soil and amendments you did to the soil when you planted it.

Thanks darlin