There are several reasons why hydrangea blossoms turn brown, and one of the most common causes is that the plant does not get enough water, according to Hyannis Country Garden. The plant could also be in shock or reacting to the weather turning colder. The Old Farmer's Almanac reveals brown buds can be pruned once they are completely dead.
Hydrangeas need partial shade in the afternoon, or the plant may get too hot as it grows. To ensure the plant stays hydrated, regularly water hydrangeas during hot weather, and maintain a layer of mulch at the base of the plant to help retain water in the soil. A soaker hose alleviates any water issues in the soil. Move the plant to a shady afternoon spot to prevent hydrangeas from getting too much sun in the summer. Grouping hydrangeas together helps reduce water consumption and doesn't flood other plants in a garden.
Brown buds also form when the weather turns cold. Gardeners can either prune the dead blossoms in the spring after new blossoms appear or just let the plant grow new material. Pruning dead stems should not be done until after the late summer. Brown leaves and brown edges may be the result of insects or diseases, according to the Old Farmer's Almanac.