These 8 Plants Are the Worst Companions for Sunflowers, Experts Warn

Potatoes

Plant heavy-feeding potatoes away from sunflowers to ensure each plant gets the proper amount of nutrition and to keep them safe from contagious diseases. "Potatoes need a consistent supply of nutrients and moisture to develop their tubers. When paired with sunflowers, they often struggle to get enough, leading to smaller, less robust harvests," says Sally McCabe, associate director of community education at Pennsylvania Horticultural Society. "Sunflowers also sometimes host fungal diseases like white mold, which can jump to your potato plants and cause significant issues."

Bush Beans

Unlike pole beans, which take advantage of nearby sunflowers as natural trellises, bush beans are less likely to thrive when planted next to the towering blooms. "Bush beans don't have the climbing advantage and often find themselves outmaneuvered for light and soil nutrients, resulting in disappointing yields," says McCabe. "Stick to pole beans if you want to grow beans near your sunflowers, ensuring the beans have a clear path to climb."

Brassicas

Brassicas, including cabbage, broccoli, kale, and Brussels sprouts, are heavy feeders, making them a poor match for companion planting with sunflowers. "They demand consistent moisture and rich soil," says McCabe. "Putting them next to a sunflower is akin to placing two competitive eaters at the same small table—someone’s going to go hungry." The pairing can also make your vegetables more susceptible to pest damage. "If you're dealing with pests like cabbage butterflies, the added stress of competition won't help your brassicas fight them off," says McCabe.

Tomatoes

Tomato plants are especially affected by the allelopathic chemicals sunflowers release, making them unlikely to produce a flourishing harvest. Sunflowers' height can also be a detriment alongside tomatoes. "While a young sunflower might offer a little temporary shade, as it matures, its sprawling leaves will block out crucial sunlight," says McCabe. "You'll likely end up with fewer flowers, poor fruit set, and leggy, unproductive plants."

But tomatoes aren't the only victim in this pairing. Tomatoes are prone to wilt, blight, viruses, and cankers. While these ailments tend to stay within the same family, some viruses could linger in the soil and potentially spread to your sunflowers, says head gardener Adrienne Roethling. 

Rosemary

Rosemary and other warm-climate herbs—like thyme or lavender—grow best in full sun and well-drained soil, making it difficult for them to get the sunshine they require when grown next to sunflowers. "Being cast into deep shade by a towering sunflower will leave them weak, spindly, and less aromatic, rather than the robust, fragrant plants we desire," says McCabe.

Hydrangea

Hydrangeas and sunflowers require different soil types, with hydrangeas preferring acidic soil, making them unsuitable companions. Hydrangeas can also crowd nearby sunflowers, depending on the type you grow. "Hydrangea is a large group of plants with dozens of species and countless cultivars and varieties; some species reach 2 to 3 feet tall, while others can grow like small trees," says Roethling. "The plant can quickly crowd nearby plants, as well as cast too much shade."

Canna Lily

Oversized canna lilies are striking additions to your landscape, but they draw Japanese beetles that turn the large leaves into skeletal shapes by the end of the growing season. "There are other plants that attract the beetles, but the canna seems to be very appealing," says Roethling. "Once the beetles are there, they tend to eat other plants in sight—best to keep desired plants away."

Mint

Whether you grow mint to dry for tea, add it to your favorite desserts, or use it as a natural way to repel garden pests, this herb is best grown in containers away from your sunflowers. When grown in your garden bed, the roots can damage surrounding plants as they spread. "Avoid placing mint in the ground, as the roots form a thick mass that could crowd the roots of fruit trees," says Roethling. "If left alone, mint will be hard to control, and removing it will take years."