10 Plants You Should Never Grow Next to Dahlias

Dahlia flowers closeup — Credit:
Jena Ardell / Getty Images

The intricate forms, long-lasting blooms, and rainbow hues of dahlias make the flower a beloved addition to many gardens. But planting dahlias alongside the wrong companions can prevent the flowers from thriving as they compete for nutrients, become overpowered by shade, or fall prey to pests and diseases drawn by neighboring plants. To help your dahlias reach their full potential, experts say to avoid growing dahlias next to the fruits, flowers, and herbs on this list.

Grace Lam, founder of Fivefork Farms, a cut flower farm spanning 38 acres of rolling fields and woodlands
Adrienne Roethling, head gardener for a private estate and former curator of Juniper Level Botanic Gardens at Plant Delights Nursery

01 of 10

Roses

The timeless look and iconic aroma of roses make them a worthwhile addition to the garden, but planting these flowers alongside dahlias will require extra care and fertilization, says Grace Lam of Fivefork Farms. Roses, like dahlias, are heavy feeders, meaning they will compete for nutrients if grown next to one another. While it's not impossible to pull off, it will require more frequent fertilizer applications.

02 of 10

Chives

Chives are a delicious and easy-to-grow herb with a potent aroma that deters rabbits and other pests. That said, one pest chives do attract is aphids, which can endanger your dahlias. "Aphids spread diseases, so it is best to plant them far away from desired plants," says Adrienne Roethling, a head gardener for a private estate.

03 of 10

Walnuts

Native walnut trees pose several issues when grown next to dahlias. These trees grow up to 90 feet tall, casting too much shade over sun-loving dahlias. Roethling adds that walnut fruits are large and can damage understory plants when they fall. "In addition to its size and large fruits, most parts of the walnut tree release a chemical that toxifies when it reaches the air. Some plants are sensitive to the toxin and fail to grow. Even if a walnut tree is removed from the landscape, the chemical will linger in the ground for years."

04 of 10

Tomatoes

Tomatoes are susceptible to several diseases that can impact the soil for surrounding plants, including dahlias. "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," says Roethling. "It is also best to remove and discard infected plant parts as they fall. Fungal wilt and tomato mosaic virus could infect non-solanaceous plants."

05 of 10

Canna Lilies

pink canna lily blooming — Credit:
Eleni Saitanidi / Getty Images

Eye-catching canna lilies are a dramatic addition to gardens, but the soft leaves attract Japanese beetles that will also feast on your dahlias. "Canna lilies are a beast in the garden with their massive sizes, larger-than-life leaves, and gorgeous tropical-like blooms. They come in many colors, many leaf patterns, and bloom for an incredibly long time during the summer months," says Roethling. "Once the beetles are there, they tend to eat other plants in sight. Best to keep desired plants away."

06 of 10

Summer Squash

A bright yellow squash blossom opens — Credit:
KenWiedemann / Getty Images

The wide, flat foliage of summer squash can cause problems for dahlias. While the leaves act like a ground cover to suppress weeds, they lie close to the ground and are susceptible to powdery mildew, says Roethling. This fungal disease can spread to nearby plants. Trellising summer squash to keep the foliage off the ground can help prevent this, but it's best to grow this plant away from your dahlias to ensure the blooms stay healthy.

07 of 10

Mint

While the wide range of options for mint plants—including lemon mint, spearmint, and chocolate mint—make it a popular garden staple, its invasive root system means you should only grow it in containers, says Roethling. "If left alone, mint will be hard to control, and removing it will take years," she says. Mint plants can starve dahlias of nutrients, reducing their flower production and overall health.

08 of 10

Morning Glory

Morning glory flowers are prolific and grow and spread quickly. While this can be a positive in the garden, it won't do your dahlias any favors. These plants can self-seed by the thousands, Roethling says. "Seedlings will come up by the masses and quickly reach 15 to 20 feet tall and wide. They can completely engulf neighboring plants," she adds.

09 of 10

Elephant Ears

Taro Plant - Elephant Ear Plant — Credit: GETTY IMAGES

Elephant ear plants grow wide enough to challenge dahlias for precious space and resources. "Elephant ear leaves can reach up to 5 to 6 feet across, and the plants will overpower smaller plants nearby," says Roethling. "Best to keep dahlias away to avoid root competition."

10 of 10

Lavender

Dahlias need consistently moist soil, making them a poor companion for drought-tolerant lavender. "I wouldn't put plants that need the soil to dry between waterings next to dahlias," says Lam. "Dahlias don't like to be dry—ever. In the hot days of summer, we sometimes water dahlias twice a day, so avoid plants that do not like constant moisture."

10 Plants You Should Never Grow Next to Dahlias, According to Gardening Experts