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Hydrangeas are popular shrubs known for their large and colorful flower heads, making them a favorite in many gardens. And for good reason, as they are quite stunning.

Thanks to their attractive foliage and long-lasting blooms, hydrangeas can enhance a variety of garden settings, including mixed borders, woodland areas, and along foundations or in shrub borders. They grow best in well-drained, nutrient-rich soil with plenty of moisture.

Although hydrangeas can be compatible with many plants, some can adversely affect their growth. Certain plants may compete for nutrients and water, hindering the growth of hydrangeas or even causing them to die. It’s important to select the right companion plants for your hydrangeas to thrive. Here are 14 plants you should never grow next to your hydrangeas.

Black Walnut Tree

black walnut green fruit
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Black walnut trees produce juglone, a substance toxic to many plants, including hydrangeas. This chemical inhibits the growth of hydrangeas and other sensitive plants nearby. Additionally, the extensive root system and large canopy of black walnuts create competitive conditions unfavorable for hydrangeas.

Sunflower

Sunflowers
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Sunflowers thrive in full sun and hotter conditions, making them quite different in their needs compared to hydrangeas. The stark contrast in their requirements can lead to competitive growth if planted too close together. It’s best to plant sunflowers in a separate area where they can enjoy the full sunlight without affecting the growth of hydrangeas.

Lilac Bush

lilac bush
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Lilac bushes prefer full sun and alkaline soil, contrasting sharply with the acidic soil and partial shade that hydrangeas need. While both are beautiful, lilacs and hydrangeas will compete for moisture and space, and the soil pH necessary for lilacs can hinder hydrangea health.

Rosemary

rosemary
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Rosemary is a perennial herb that flourishes in sunny, dry environments and prefers lean, well-draining soil. This makes it a poor match for hydrangeas, which thrive in moist, slightly acidic soil and benefit from some shade.

Because rosemary and hydrangeas have such different needs for sunlight and soil, planting them close together can lead to problems. Rosemary may dominate the available resources, depriving hydrangeas of the moisture and nutrients they need to thrive.

Peppers

Red pepper on a plant. Gardening
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Peppers are another high-sun, low-water plant that conflicts with the needs of hydrangeas. While peppers do well in containers that can be managed separately, planting them in the ground alongside hydrangeas can result in competition for water and nutrients, with peppers likely dominating the relationship.

China Aster

china aster
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China asters require full sun and good air circulation to thrive, conditions that do not align well with the needs of hydrangeas. If planted too close, asters may not receive enough sunlight and space to flourish. It’s best to plant them separately to optimize the health and blooming of both plants.

Amur Maple

amur maple
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Amur maple, while smaller than many trees, still competes intensely with hydrangeas for root space and nutrients. Despite its tolerance for partial shade, its root competition and preference for well-draining soil can stress nearby hydrangea plants, making close planting inadvisable.

Squash

Courgette (zucchini) plants growing in a raised bed in a UK vegetable garden in summer.
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Squash plants, including zucchini, are vigorous growers and heavy feeders that require a lot of space and nutrients, which can deprive hydrangeas of essential resources. Their differing needs for mulching and full sun make them incompatible with hydrangeas in a shared garden space.

Oak Tree

oak acorn tree
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Oak trees create a challenging environment for hydrangeas due to their large size and dense canopy. This can limit sunlight and space for hydrangeas, and their extensive root systems compete heavily with hydrangeas for water and nutrients. Planting hydrangeas too close to oak trees can severely inhibit their growth.

Lavender

lavender in field
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Lavender and hydrangeas are fundamentally mismatched in a garden setting. Lavender loves full sun and dry, alkaline soil, whereas hydrangeas flourish in moist, slightly acidic conditions.

Asparagus

asparagus
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Asparagus and hydrangeas have conflicting soil pH preferences, making co-planting them problematic. Asparagus thrives in alkaline soil, while hydrangeas prefer acidic conditions. Keeping these plants separate helps avoid compromising their soil needs and ensures better growth and health.

Sedum Burrito

sedum burrito
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Sedum burrito is a succulent that thrives in dry, sunny locations. Its need for minimal water and high light does not complement the moist, semi-shaded environment preferred by hydrangeas, making them unsuitable garden friends.

Dwarf Bearded Irises

dwarf iris
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Dwarf irises enjoy the sun to partial shade and well-drained soil but do not fare well in the dense shade or moist soil that hydrangeas may create. While tough, their preference for drier conditions makes them poor companions for hydrangeas, which can lead to water competition.

Tender Geraniums

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Tender geraniums are well-suited to hot, sunny, and dry conditions, quite the opposite of what hydrangeas require. While they can make visually appealing neighbors, the fundamental differences in their growing conditions mean they should not share the same garden space.

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Flowering-Quince
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