container gardening, can you use the soil again next year in the container for the same or different vegetable?

Answer 1

You can but if you grow same think year after year that won't be good. If your growing tomatoes you can grow legumes and that will replenish the nitrogen in the soil. If you don't rotate you can add compost which will help plants that need nitrogen replenished.

Answer 2

You also risk bugs and diseases from the year before.  New bagged soil is cheap insurance.

Answer 3

Sure, but either rotate your crops to provide the used nitrogen or refresh soil with compost... Simply planting nitrogen fixing plants during off season is a wonderful help to soil. Vetch, wild sweet peas, winter wheat & clover are all wonderful & can be later tilled into ground to feed future plants.

Hope that helps.