Potatoes should not be planted near tomatoes because they share similar growing requirements and are susceptible to the same pests and diseases, which can spread through the soil. Instead, plant potatoes away from tomatoes
Eggplants are not good neighbors for tomatoes because both are prone to early blight, a fungal disease that can easily spread between them. To prevent this, keep eggplants and tomatoes separated, and consider planting beans
Corn should not be planted near tomatoes because it attracts corn earworms (also known as tomato fruitworms) that can damage both crops. To avoid pest infestations, do not plant corn and tomatoes together.
Brassicas (such as cabbage, broccoli, and kale) compete heavily with tomatoes for nutrients, potentially stunting tomato growth and fruit production. To ensure your tomatoes have enough nutrients to thrive, plant them away from all brassicas.
Dill is not a good companion for tomatoes because as it matures, it releases allelopathic chemicals that can inhibit tomato growth. Plant dill near other crops like cucumbers, onions, lettuce, basil, and Brassicas, but away from tomatoes.
Fennel inhibits the growth of many plants, including tomatoes, due to its allelopathic properties. Grow fennel in a separate area of the garden to avoid negative impacts on surrounding plants.
Walnut trees produce juglone, a chemical that is toxic to tomatoes and many other plants. To protect your tomatoes, avoid planting them near walnut trees and consider using container gardening if space is limited.