15 Plants to Never Grow Next to Zinnias, According to Experts

Garden bed planted with Zinnias — Credit:
Getty Images

Zinnias are eye-catching annual flowers that are available in various colors, shapes, and sizes, filling the garden with beauty from late spring until the first frost. While zinnias are low-maintenance flowers that thrive with minimal care, one way to get the most from your crop is to be mindful of the plants you're growing next to zinnias.

These plants require full sun, well-draining soil, and plenty of nutrients to thrive, which means they should not be planted next to tall plants that cast too much shade or other heavy feeders. Zinnias are also prone to powdery mildew, which can occur due to a lack of airflow, so they shouldn't be planted next to species that will overcrowd them.

To ensure healthy zinnias that bloom for weeks at a time, we spoke to gardening experts who shared the plants you should never grow nearby.

Damon Abdi of the Hammond Research Station at Louisiana State University's AgCenter
Linda Langelo, horticulture specialist at Colorado State University and author of Plants Are Speaking. Are You Listening?

01 of 15

Impatiens

Impatiens (Impatiens spp.) are popular flowers that add color to the landscape during summer, like zinnias. "However, most varieties of impatiens prefer shady conditions in order to thrive," says Damon Abdi of the Hammond Research Station at Louisiana State University's AgCenter. "Sun-loving zinnia and shade-loving impatiens would not make sense to plant next to each other due to differences in preferred light conditions."

02 of 15

Astilbe

Astilbe (Astilbe spp.) produces cheerful plumes of uniquely textured flowers in bright colors. However, like impatiens, astilbe is a shade-loving plant that shouldn't be grown next to zinnias, as their sun preferences differ, says Abdi.

03 of 15

Corn

Corn (Zea mays) is a heavy feeder that competes with neighboring plants for nutrients. Moreover, corn is a fast-growing plant that can reach considerable heights when it matures. "Between the competition for nutrient resources and the shade cast by corn as it grows, planting zinnias and corn next to each other would not make sense in a garden," says Abdi.

04 of 15

Morning Glory

The fast-growing vining habit of morning glory (Ipomoea) can be a welcome addition to the garden, but keep it away from zinnias. According to Abdi, the upright nature of zinnias provides a perch for the morning glory's vines to twine upon. "This may pose a nuisance in a zinnia garden, particularly if cut flowers are desired," he says.

05 of 15

Bigleaf Hydrangea

Bigleaf hydrangeas (Hydrangea macrophylla) are beloved for their large blooms that fill gardens with beauty in summer. "However, when put in overly hot, bright conditions, this plant suffers," says Abdi. "Zinnias, on the other hand, thrive in the full sun." Both plants are great in a garden, but they shouldn't be planted in the same area.

06 of 15

Lavender

Lavender (Lavandula) is a fragrant favorite that thrives in hot conditions and can prevent pests from bothering your garden, but it's not ideal as a zinnia companion plant. "Lavender plants will suffer from root rot next to zinnias," says Linda Langelo, horticulture specialist at Colorado State University. This is because lavender prefers drier, well-drained sandy soils, while zinnias need regular watering until they're established.

07 of 15

Marigolds

Marigolds (Tagetes minuta) are the perfect companion plants for many vegetables; however, these flowers release certain chemicals that stunt the growth of zinnias. "It is called alpha-terthienyl, a phototoxin," says Langelo. "It is great for suppressing nematodes and for use as an insecticide, but not for zinnias."

08 of 15

Cucumbers

Cucumbers (Cucumis sativus) are heavy feeders that compete for the same nutrients as zinnias. Additionally, cucumbers attract cucumber beetles that will damage zinnias, says Langelo, adding that cucumbers and zinnias are both affected by powdery mildew.

09 of 15

Tomatoes

Tomatoes (Solanum lycopersicum) rob the soil of potassium and phosphorous, which zinnias need in large quantities to thrive. Tomato vines can also sprawl and crowd out zinnias, says Langelo. This can be especially problematic as zinnias can suffer from powdery mildew if they don't have enough airflow.

10 of 15

Pumpkins

Pumpkin growing pumpkin patch — Credit: PhotoAlto/Jerome Gorin / Getty Images

Pumpkins (Cucurbita spp.) sprawl and crowd out zinnias, potentially causing powdery mildew due to a lack of airflow. "Plus, they utilize the same nutrient demands," Langelo says, adding that pumpkins deplete the soil of nitrogen. What's more, pumpkins and zinnias attract the same insects, including squash bugs and beetles.

11 of 15

Mint

Mint (Mentha) is typically a no-go in the garden. "Mint is a very aggressive plant. It would choke out zinnias and rob nutrients from the soil," says Langelo. "Mint releases menthone, which inhibits the growth of any neighboring plants." If you want to grow this herb, make sure you plant it exclusively in pots and containers.

12 of 15

Fennel

Fennel (Foeniculum vulgare) releases flavonoids that will inhibit zinnia seeds from germinating. Even if you purchase young zinnia plants instead of growing from seed, fennel can still stunt their growth and prevent the plants from reaching maturity, says Langelo.

13 of 15

Rosemary

Rosemary (Salvia rosmarinus) and zinnias have different soil and water requirements. "Rosemary likes a well-drained, dry soil and is drought-tolerant," says Langelo. "Zinnias need more regular watering until they are established. The amount of water zinnias need as young seedlings will cause root rot for the rosemary."

14 of 15

Squash

Like other cucurbits (Cucurbita maxima), squash will compete for the same essential nutrients as zinnias. Squash is also a vining plant that can take over the garden, crowding zinnias out of the space they need to grow and stay healthy.

15 of 15

Sunflowers

Sunflowers (Helianthus annuus) are a beautiful and cheerful addition to the landscape, but they're not suitable for growing next to zinnias. The sunflowers will shade out the zinnias and stunt their growth, says Langelo, adding that sunflowers can even prevent the germination of zinnia seeds.