Hydrangea blooms can make for fabulous floral arrangements, especially the mophead varieties, which are so large, they can fill a vase with its many tiny flowers. They also keep very well, especially with a few precautions. Since new flowers frequently bud on old wood, cut the green part, not the brown area of the stem. This will ensure that new blooms will delight you the next year. You may expect properly cut blooms to last for at least several weeks to a month.
Floristry experts suggest that you make certain the flower is at least a week old and is fully colored prior to cutting it since the older the bloom, the longer the cut flower will last in water. Once the bloom is cut, which should be cut on a diagonal, the hydrangea should be immersed in water for two hours. To increase water absorption, you can either smash the bottom of the stem with a hammer, or cut 1 inch (2.54 cm) off the bottom of the stem while it is immersed in water. This will keep the bloom alive and drinking water for a longer period of time.
Some experts recommend boiling the water and then chilling it before soaking of the bloom. Others simply recommend keeping the stem well immersed in water. Consider using a shorter vase, and cutting the hydrangea stem short, about 6 inches (15.24 cm) or less. A longer stem requires more water and will shorten the life of the bloom. Since the stem will take up water, check longer stems frequently to see if the water in the vase needs to be replaced.
Though hydrangea leaves are pretty, they should all be trimmed off a bloom. They will also steal water from the flower part and shorten the life of a cut flower. Also, do not trim non-blooming stalks on a plant less than five years old because they tend to become next year’s flowers. Cutting with caution is, therefore, recommended.