Walnut trees release juglone, a chemical toxic to hydrangeas, which can stunt their growth or even kill them.
Mint is highly invasive and can quickly take over the area, competing with hydrangeas for nutrients and space.
Eucalyptus trees can deplete the soil of water and nutrients, making it difficult for hydrangeas to thrive nearby.
Sunflowers are heavy feeders and can rob the soil of nutrients that hydrangeas need to grow healthy and strong.
Tall grasses can overshadow hydrangeas, blocking the sunlight they need and creating too much competition for water and nutrients.
Bulbs like daffodils prefer dry conditions during dormancy, while hydrangeas need consistent moisture, making them incompatible companions.
Herbs like rosemary prefer drier, more alkaline soils, while hydrangeas thrive in moist, acidic environments, leading to poor growth for both.