15 Plants That Could Be Hurting Your Hydrangeas Without You Realizing It

Hydrangeas are a staple of the shade garden, renowned for their vibrant blooms. These flowering shrubs thrive in dappled shade, well-draining soil, and consistent moisture. They make great companions for other shade-loving staples, such as hostas, astilbe, ferns, coral bells, and more.

However, not all plants pair well with hydrangeas in the garden. Several plants are incompatible with these gorgeous shrubs, whether due to differing growing requirements or a because they outcompete them for nutrients or water. 

Here are the top 15 plants that you should never grow near hydrangeas if you want them to thrive.

Cheery sunflowers may seem like they’d go with anything, but the experts agree it’s best to avoid planting them too close to hydrangeas.

In addition to enjoying different growing conditions (sunflowers love the sun), sunflowers are also known for being mildly allelopathic, meaning they release chemicals that can inhibit the growth of other plants, including sensitive hydrangeas. 

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Lavender and hydrangeas may look pretty in bouquets together, but they are incompatible as neighbors in the garden. This is due to their drastically different growing needs, says Lorraine Bellato, a professional horticulturist and hydrangea expert.

Lavender loves dry, hot, and sunny conditions, while hydrangeas enjoy consistent moisture and some shade to provide some relief from the sun. 

Marigolds are prized as ideal companion plants for a variety of garden staples, especially vegetables and herbs. However, they’re not a good match for hydrangeas, according to Ondrea Kidd, lead floral designer and founder of Sowing Joy Farm.

Marigolds are allelopathic, secreting a chemical that can be helpful for some plants (like vegetables) but can be harmful to hydrangeas.

Like hydrangeas, dahlias are prized for their stunning summer blooms. However, they shouldn’t be planted beside each other in the garden.

Dahlias and hydrangeas enjoy different growing conditions, so you won’t be able to please them both in a single location in the garden. Keep dahlias in hot, sunny locations and hydrangeas in partially shaded spots of your landscape. 

Roses and hydrangeas are both icons of the cut flower garden, but they shouldn’t be grown in close proximity, according to Kidd. 

“Although roses and hydrangeas look stunning coupled together in an arrangement, they do not grow well together due to their differing preferences in soil type, light, and their overcrowding tendency,” she says. 

Goldenrod is another allelopathic plant that can hinder the growth of hydrangeas in the garden, says Kidd. This trait makes it a successful competitor in wildflower gardens and naturalized landscapes, but hydrangeas are sensitive to its allelopathic properties.

Spring bulbs, such as daffodils, are a no-go next to hydrangeas, according to Bellato. In addition to being allelopathic, daffodils have different water needs from hydrangeas, making them incompatible neighbors. 

“The water needs of a hydrangea will rot them,” she says. “The bulbs need to be on the dry side once they have finished flowering.”

Tulips are another popular spring bulb that shouldn’t be planted too close to hydrangeas. While they aren’t allelopathic, tulips prefer full sun conditions and soil that’s on the dry side, similar to daffodils.

These differing growing requirements mean that it’ll be challenging to make both tulips and hydrangeas happy in the same location.

This flowering shrub is prized for its showy spring display, but should be kept far away from hydrangeas in the garden. Unfortunately, forsythias are allelopathic and can inhibit the growth of hydrangeas if they are planted directly beside one another. 

Fennel

Another allelopathic plant that doesn’t play nicely with hydrangeas is fennel. In fact, fennel can be challenging to grow near a number of plants, including those in the nightshade family (such as tomatoes, peppers, and potatoes). Try growing fennel in containers to prevent accidentally damaging nearby plants.

Due to its aggressive and invasive nature, mint is not a suitable choice for planting near hydrangeas. In fact, let’s keep this one out of the garden beds altogether, shall we? Mint is best planted in pots and containers to help control its growth and prevent it from spreading. 

Raspberry bushes can make a great addition to the garden, providing fresh and delicious fruit throughout late spring and through summer.

However, raspberries can also be aggressive, spreading quickly and taking over gardens. A hydrangea bush planted too close to a raspberry bush will soon be crowded out, says Kidd. Keep raspberry bushes in a dedicated area of the garden to help control their spread!.

Garlic’s allelopathic properties are well-known, making companion planting with garlic a pretty strict process.

Unfortunately, if you’re hoping to grow both garlic and hydrangeas, it’s best to avoid planting them close to each other, as the chemicals released by garlic can be harmful to hydrangea plants.

While hydrangeas enjoy a bit of shade, avoid planting them too close to large trees that will prevent any sunlight from reaching them, especially black walnut trees. Not only do black walnut trees create a dense canopy and deep shade conditions, but they are also allelopathic, says Kidd.

Another large tree to avoid near hydrangeas is the willow tree. Not only will it shade out a hydrangea, but willow trees are notoriously nutrient- and water-hungry, meaning it would likely outcompete a hydrangea for resources in the soil.