14 Plants You Should Never Grow Next to Hydrangeas
Hydrangeas tend to be a fan favorite for landscaping—and they look gorgeous paired with so many different kinds of plants and shrubs. But unless you’re looking for a toxic relationship—and perhaps, a dead plant or two—you should probably avoid placing your hydrangea too close to these other popular garden plants.
Garden experts recommend keeping these trees, shrubs, and plants far away from your hydrangeas for a variety of reasons—so keep this list handy when you’re plotting out your landscaping to help ensure everything stays healthy.
Lavender
Lavender would look lovely next to a hydrangea bush, with its purple, spiky blooms a perfect foil to the globe-shaped purple, blue, or pink hydrangea blooms. But lavender requires dry, hot, and sunny spots to thrive—and that’s not the best situation for hydrangeas.
“Hydrangeas need regular and possibly extra water during the warm months to keep their foliage looking full and their flowers blooming, otherwise they are prone to drooping in the heat of the day,” says Bethany Lakatos, plant expert at Fast Growing Trees. “For this reason, it’s best to plant them away from dry-site plants like lavender, whose roots are sensitive to overwatering.”
Black Walnut Trees
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Who knew that some plants can actually poison other plants? That’s the reason why black walnut trees and hydrangea are a toxic combo. “Black walnut trees release the chemical juglone, which some plants like hydrangea are sensitive to,” Lakatos says. “Because the highest concentration of juglone is in the root zone of black walnuts, hydrangeas should be planted at least 60 feet away from black walnuts.” If you plant hydrangea arborescens (aka, smooth hydrangea), they may be able to handle a bit of a closer range.
Roses
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While roses and hydrangeas make a gorgeous cut bouquet, they shouldn’t be near each other in the garden. “Hydrangeas like some shade and moist, rich, slightly acidic soil,” says Megan McConnell, plant information director at Monrovia. “Plants that like lots of sun, heat, and dry conditions aren’t going to do well in those condition. Roses are a good example of sun-loving plants that like drier conditions.”
Sunflowers
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Sunflowers love full sun, but that’s not the only reason that it’s not a great neighbor for hydrangea. “Some plants emit chemicals that inhibit the growth of adjacent plants, a process known as allelopathy,” says Kevin Lenhart, design director for Yardzen. “Many plants are allelopathic to some degree, including sunflowers.”
Rosemary
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Rosemary’s spiky leaves and tiny blooms would be a nice contrast to the grand flowers and leaves of a hydrangea, but this is another case of a mismatch between plant needs, as rosemary prefers sunny spots and dry conditions.
Goldenrod
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The pop of yellow would look beautiful with the cooler hues of hydrangea, but goldenrod also tends to be allelopathic and can harm your hydrangea plants.
Sedum
If you’re looking for a flowering plant that does well in dry conditions, hardy sedum is your plant. But if you’re looking for a great companion for your hydrangea, this definitely is not it.
Marigolds
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Marigolds are a garden favorite for repelling pests, but you should also keep them away from your hydrangea, as they need very different growing conditions.
Garlic
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While planting edible plants in with your flowers is always a cool combo, keep garlic far away from your hydrangea. It also produces the allelopathic chemicals that’ll stunt your hydrangea’s growth.
Thyme
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This perennial herb is another one that prefers the dry, sunny spots that aren’t good for hydrangeas. Unless you have a sunny spot adjacent to your hydrangead and can do very targeted watering, one of your plants will end up very unhappy.
Agave
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Agave plants thrive in sunny, arid spots and drought-prone areas—which means that they need very different growing conditions than hydrangeas do.
Yucca
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Yucca plants are another favorite for dry, drought-like conditions—which hydrangea definitely don’t appreciate. It needs to be placed in full sun, so pop this on a west-facing part of your landscape where it can enjoy the light.
Forsythia
Forsythia may seem like a great companion plant for hydrangea, as it produces bright yellow blooms in springtime, before hydrangea puts on their show in the summer. But Lenhart says this is another plant that engages in allelopathy, and could slow or stunt the growth of your hydrangea.
Large Trees and Shrubs
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While hydrangea are noted for thriving in shady spots, you want to keep them a bit clear of grand trees. “Large trees and even large shrubs can cause harm to hydrangeas and other plants, both by blocking incoming light and by outcompeting them and consuming all the available resources,” Lenhart says.
You should especially watch out for willow trees, McConnell says. “You should avoid plants that are water hogs, like willows.”
Tips for Finding Plants to Pair With Hydrangeas
Choose plants with similar water, soil, and fertilizing needs
Look for plants that require the same conditions as your hydrangea for an ideal combination, Lenhart says. “Putting low-water plants next to hydrangeas will result either in an under-watered hydrangea or an overwatered neighboring plant.” Check out our list of the best companion plants for hydrangeas to find an option that not only looks great but also keeps your hydrangea happy.
Think about color combos
Choose a color combination that’ll add some wow to your garden. “Complementary colors for blue hydrangeas are yellow and red, along with silver or grey foliage,” Lakatos says. “Consider coreopsis, yellow echinacea, daylilies, and rudbeckia for yellow plantings with blue hydrangeas. Purples and lavenders like salvia and speedwell offset pink hydrangeas.”
Consider plants that’ll provide benefits for your hydrangea
While the plants above can inhibit the growth of your hydrangea, some plants can be beneficial to their growth. “Echinacea purpurea (purple coneflower) has a deep tap root, which helps to maintain the good drainage that hydrangeas require,” Lenhart says. “They also happen to be native to a wide swath of the U.S., and very beneficial to pollinator species.”
Look for plants with different bloom times
When you’re plotting out your garden, you want to ensure that you get a variety of plants so you enjoy blooms and something interesting all year long. Since hydrangea tend to have summer and fall covered, you’ll want to look at some spring bloomers or evergreen options. “Evergreen shrubs like holly or boxwood are classic examples, but prairie dropseed grass can lend a meadowy look to a hydrangea arrangement,” Lenhart says. “In shadier spots, evergreen ferns work well and also contribute that much needed winter interest.”
