Dry soil can be the death of Hydrangea. Leaves that turn yellow and fall off are a sign of dry soil. Flowering plants are thirsty, so it's a good idea to check the soil every day while in bloom.

Blue Hydrangeas need acidic soil (pH 5.5 and lower) or they will change flower color from blue to pink. Alkaline soils (higher than pH 7) are fine for pink varieties. To keep the blue color, add sulphur while the plant is blooming. Neutral pH (between pH 5.5 and pH 7) can make the flowers purple or a mix of pink and blue. It's important to know that not all cultivars can change to blue, so buy the color you want and try to maintain it.

If you intend to keep your Hydrangea indoors, repot after flowering and cut the stems back by half. Keep the plant cool during the winter, then move it to warmer conditions in late winter to help bring it into bloom.

Hydrangeas don't need to be pruned back unless you want to control their size. Cutting off about 1/3 of the oldest stems will give you a fuller plant. When to prune hydrangeas: After blossoms fade.