I had no clue about this

Some plants can attract pests that are particularly harmful to tomatoes. For instance, fennel can attract aphids and other insects that may spread to tomato plants. Additionally, cabbage and other members of the brassica family can attract pests like cabbage worms and whiteflies, which can also harm tomatoes. Avoiding these plants near tomatoes can help reduce pest pressure.

Certain plants can inhibit the growth of tomatoes through various means. For example, black walnut trees release juglone, a chemical that can stunt the growth of tomatoes and other plants. Similarly, dill can inhibit tomato growth if planted too closely, as it can compete for nutrients and space.

Allelopathy refers to the chemical inhibition of one plant by another due to the release of toxic compounds. Walnuts, particularly black walnuts, are known for their allelopathic effects on tomatoes. The juglone compound they release can severely inhibit tomato growth and even kill the plants if they are too close.

Some plants require vastly different growing conditions than tomatoes, making them poor companions. For example, potatoes prefer cooler soil temperatures and can suffer from diseases that also affect tomatoes, such as blight. Growing these plants together can lead to increased disease pressure and suboptimal growing conditions for both.

Tomatoes require full sun to produce the best yields. Plants that grow tall and bushy, such as sunflowers, can cast shade over tomato plants, reducing their access to sunlight. This can lead to leggy growth and reduced fruit production. It’s important to ensure that tomatoes receive adequate sunlight by avoiding tall plants that may overshadow them.