For years and years we’ve planted tomatoes (different varieties) along the side of my garage, where there is a southern exposure. But for the last several years the plants have done progressively worse and worse, in spite of adequate watering and fertilization. I know that farmers rotate their crops to avoid depletion of the soil, and I’m thinking of doing the same thing. So what would be a good “crop” to plant in that area?
I also intend to plant tomatoes somewhere else, just to see what happens.
Look to shade, toxicity, disease, and pestilence as the problem. I eliminated nutrition as you said that was alright.
Shade: Has a tree gotten larger and shades the spot?
Toxicity: Does your winter salt collect there. Did oil or some chemical leak there?
Disease: Once a disease shows up you need to plant something that doesn’t support the life cycle of the fungus or virus.
Pestilence: The insects will eat the plants and spread the diseases that attack the plants. Plant something that disrupts the life cycle of the insect.
Plant french marigolds. They will disrupt the tomato pests and diseases. French marigolds will kill nematode infestations too. Make sure they are french marigolds to control the nematodes. Planting other marigolds will disrupt any of the other pests and diseases. Sometimes I will plant them around tomato plants to discouraging pests. Wrap a newspaper collar around a tomato transplant stem where it comes out of the soil to protect against cut worms if they are a problem.
As madrabbitwoman says, some sort of legumes (runner beans, scarlet beans, broad beans) will actually renew the nitrogen in the soil (they have symbiotic bacteria that “fix” nitrogen). Not only will you get beans for your troubles, you’ll get fertilizer, too!