Hydrangeas were favorites in 19th century gardens. Compact bushes bloomed for a long period and held onto blooms straight through winter. Today's newer hybrids join improved historic varieties to provide fresh colors and shapes on the same sturdy bushes. Keeping a cut hydrangea flower bright for use in a wedding bouquet or summer party is almost as easy as drying the old arborescens and modern mophead varieties. Use a few simple techniques and your flowers should stay fresh for days.
Fill a tall florist's bucket or other container with water and take it to the garden. Cut flowers and place the stems in water immediately and carry the bucket to the cleaning table. Cut hydrangeas in the cool of early morning when plants have not yet begun to evaporate moisture in the heat of the day.
Clean all but a few leaves from each flower's stem as they rest in the bucket. Leaves, especially large hydrangea leaves, can divert water from flowers on the end of the stem. While you are cleaning stems, put some water on to boil in a kettle on the stove or in the microwave.
Prepare a vase filled with room-temperature water and fill a dipping bowl or tea cup with boiling water. Another method uses alum rather than hot water in the dipping bowl.
Cut a few stems and stand them in the hot water for 30 seconds or touch their ends to the powdered alum. Place them immediately into the vase of room-temperature water. Arrange the flowers after all the stems have been dipped. Use florist's preservative in fresh water if desired but don't add it to water with stems that have been dipped in alum.
Change the water every day to keep flowers fresh. If a bloom begins to wilt, recut its end and plunge it into hot water before returning the stem to its vase. Studies at the University of Kentucky established a range from five to seven days of freshness for properly hydrated panicle (H. paniculata) hydrangeas. Mopheads (H. macrophylla) or Annabelles (H. arborescens) should last longer.