What is the best container size to use for tomatoes? Well, it seems that the answer is any size that works. I wouldn't have thought that I'd get any decent results planting Siletz Organic(a determinate variety) in a container the same size as the ones I use for cherry tomatoes. But as you can see, this plant has produced nice sized fruit. I guess the potting soil/compost mix along with some organic liquid fish fertilizer did the trick. Don't you just love it when an experiment is successful?