Insufficient watering - Hydrangeas need about an inch of water per week. If they don't get enough, the leaves and flowers will start to wilt and turn brown.
Too much sun - Most hydrangeas prefer partial shade, getting only 4-6 hours of sun, especially in the cooler morning hours. Planting them in full sun can cause the flowers to brown quickly.
Transplant shock - Moving a hydrangea exposes it to stress, often leading to wilting, browning leaves, and flowers turning brown. Avoid transplanting in summer, water well before and after, and provide some shade.
Fertilizer burn - Applying too much fertilizer can cause the leaf edges to turn brown and crispy. Limit fertilizing to 2-3 times per year and use slow-release formulas.
Fungal diseases - Various fungal infections can lead to white, brown or rust-colored spots on the leaves. Remove infected leaves, improve garden hygiene, and use fungicides carefully.
If you notice browning flowers, snip them off to improve the plant's appearance and encourage more blooms.
Adjust watering, sunlight, and fertilizing as needed to keep your hydrangeas healthy and colorful all season long