The question of whether to grow tomatoes and peppers together is largely a matter of personal preference, climate and gardening space. Preventing plant diseases is the main reason why gardeners do not grow these crops together, but you may never encounter a problem if you live in a dry, mild climate.
Tomatoes and peppers, as well as strawberries, potatoes and raspberries, belong to the same family and are all susceptible to verticillium and fusarium wilt. The theory goes that when grown together, these plants are more likely to spread diseases to each other. Common gardening wisdom calls for growing these plants at least 20 feet away from each other if possible, especially in hot, humid climates where fungal diseases are more prevalent.
Many gardeners don't have the gardening space to keep susceptible crops quarantined from each other. In this case, use good gardening practices to minimize the risk of disease. Buy disease-resistant tomatoes and peppers, and space them at least 2 to 3 feet apart, depending on the variety because good air circulation reduces disease. Use soaker hoses instead of overhead sprinklers to water since wet leaves spread disease, and never work in a wet garden. If you lack garden space, but prefer to separate these plants, try container plantings.
Many gardeners grow tomatoes and peppers together because they have similar growing needs. Both produce fruit on flowering plants and both require full sun, fertile soil and warm, moist conditions. If you plant tomatoes and peppers together, space them in rows at least 2 feet apart so they don't compete for water and nutrients. Watch for signs of disease and remove any dead or diseased foliage promptly. Pick fruits promptly and don't allow them to spoil on the vine.
Regardless of where you grow tomatoes and peppers in your yard, rotate them, along with other crops, so no plant grows in the same space each year. Aim for a three-year rotation before growing tomatoes and peppers in the same place. Rotating crops reduces the chances of diseases building up in the soil and also prevents soil depletion. Fruiting crops, such as tomatoes and peppers, take a lot out of the soil, while legume crops, such as peas and beans improve the soil.