lack walnut trees produce juglone, a substance toxic to many plants, including hydrangeas. This chemical inhibits the growth of hydrangeas.
Sunflowers thrive in full sun and hotter conditions, making them quite different in their needs compared to hydrangeas.
Lilac bushes prefer full sun and alkaline soil, contrasting sharply with the acidic soil and partial shade that hydrangeas need.
Rosemary is a perennial herb that flourishes in sunny, dry environments and prefers lean, well-draining soil.
While peppers do well in containers that can be managed separately, planting them in the ground alongside hydrangeas can result in competition for water.
China asters require full sun and good air circulation to thrive, conditions that do not align well with the needs of hydrangeas.
Amur maple, while smaller than many trees, still competes intensely with hydrangeas for root space and nutrients.