Hydrangeas are a garden favorite in the U.S., thanks to their vibrant blooms and versatility. However, planting them near certain plants can lead to competition for resources, mismatched care needs, or even harm. Below are 12 plants commonly grown in American gardens that should be kept at a distance from your hydrangeas, along with the reasons why.
Thyme

Thyme thrives in dry, well-draining soil and basks in full sun. These are conditions that don’t align with the preferences of hydrangeas. Hydrangeas demand consistently moist, nutrient-rich soil to support their vibrant blooms, which can lead to overwatering thyme and ultimately causing its roots to rot. The vastly different water and sunlight needs of these plants make them incompatible, as one will always suffer to accommodate the other.
Black Walnut

Black walnut trees produce a toxin called juglone, which is most concentrated in their buds, nut hulls, and roots. This toxin can harm plants like hydrangeas, causing them to wilt or even die if planted too close. The toxic effects can stretch up to 50-80 feet from the trunk, with the highest risk under the tree’s canopy. Hydrangeas, being juglone-sensitive, struggle to survive in such hostile conditions, making this pairing a poor choice.
Eucalyptus

Eucalyptus trees have deep, aggressive root systems that constantly compete for water and nutrients, which can leave hydrangeas struggling to survive. Hydrangeas need consistently moist soil, and the water-hungry eucalyptus tree can quickly deplete the resources around it. Eucalyptus trees also tend to grow tall and wide, casting dense shade that can deprive hydrangeas of the light they need to thrive, creating an unfavorable environment for them.
Lavender

Lavender thrives in well-drained dry soil, while hydrangeas need consistently moist, nutrient-rich soil to thrive. The moisture-loving nature of hydrangeas often leads to overwatering, which can suffocate lavender’s roots and cause it to die. Lavender thrives in full sun, whereas hydrangeas prefer partial shade. The stark contrast in their growth requirements makes them poor companions and difficult to grow successfully together.
Daffodils

Daffodils require well-drained soil and need about an inch of water per week during their growing season, whether from rainfall or manual watering. However, unlike hydrangeas, daffodils don’t need constant moisture and it’s important to inspect the soil regularly to ensure it’s dry before watering. After blooming, you can stop watering them. Hydrangeas, on the other hand, demand consistent moisture, which can harm daffodil bulbs by causing rot if planted too close.
Marigolds

Marigolds require well-draining soil and thrive with consistent watering, especially during hot, dry spells. While they become more drought-tolerant once established, they still need weekly watering. Hydrangeas, on the other hand, need consistently moist soil to flourish, and overwatering can harm marigolds. Their differing moisture requirements create competition for resources, making it difficult for both plants to thrive together. Hydrangeas may struggle to stay hydrated if marigolds are planted too close.
Bamboo

Bamboo is known for its rapid growth and invasive root system, which can easily overtake the area around hydrangeas. As bamboo spreads, it competes for essential water and nutrients, depriving hydrangeas of what they need to thrive. Bamboo also creates thick, dense shade that blocks the filtered sunlight hydrangeas require, ultimately stunting their growth and reducing the vibrancy of their blooms.
Roses

Roses can compete with hydrangeas for nutrients and water, especially in smaller garden spaces with limited resources. Some rose varieties prefer different soil conditions, such as more alkaline or well-drained soil, while hydrangeas thrive in moist, loamy, slightly acidic soil. These differences can create an imbalance, leaving both plants struggling.
Lilac

Lilacs thrive in areas that get at least six hours of full sun daily, as they need plenty of light to produce their beautiful blooms. They prefer loamy, slightly alkaline soil with good drainage, as poor drainage can lead to root rot and other diseases. While they can tolerate some shade, the lack of sun will result in fewer flowers. Hydrangeas, which require moist soil, are not ideal neighbors for lilacs due to these differing needs.
Anemone

While both anemones and hydrangeas enjoy partial shade, anemones can be quite aggressive in their growth. They spread rapidly, which leads to competition for water, nutrients, and space. This invasive growth can overwhelm hydrangeas, especially in smaller garden beds, leaving the hydrangeas with less access to the resources they need. As a result, hydrangeas may suffer from reduced blooming or even poor overall health.
Garlic

Garlic is relatively low-maintenance when it comes to water needs, preferring moderately moist soil. It typically requires about an inch of water per week, with more during hot spells. However, garlic needs the soil to dry out slightly before harvest. If conditions remain too wet near harvest time, mold can develop, ruining the crop. Hydrangeas, which need consistently moist soil, are not compatible with garlic’s drier, well-drained preferences.
Sunflowers

While sunflowers need regular watering encourages better blooming, it’s important to let the top one to two inches of soil dry out before waterring again. too much moisture can cause fungal diseases like powdery mildew, damaging the leaves and stunt growth. Hydrangeas, with their preference for consistently moist soil, would struggle with the watering schedule needed for sunflowers, making them incompatible neighbors in your garden.
Mint

Mint, particularly culinary varieties like Mentha spp., can be highly invasive in gardens. Its rapid growth can outcompete nearby plants, including hydrangeas, for water and nutrients. This can leave hydrangeas struggling to get the resources they need to thrive. It’s best to keep mint in a separate, controlled area to protect your hydrangeas.