These tomatoes were planted about as close as I would ever attempt. The results of this planting will determine whether or not next year’s crop is planted this way or not. The advantages of close planting are mainly from better utilization of space, but for tomatoes, it also means that they support each other. Staking is only needed for the plants on the outside edges. Disadvantages include less air flow which could mean greater potential for disease, and more difficult to pick from the inner plants.
My guess is that this will prove to be too closely planted, but it’s an experiment, so it’s not always supposed to work. No matter what a book or web site may say, you never really know what will work for your situation until you try it yourself.
Gardening is experimenting. I take notes and adapt as needed.