I always wondered if there was a secret to keeping hydrangea flowers fresh once they’ve been cut from the bush. It seemed that sometimes my flowers would last a few days, but usually they would wilt quickly once I added them to a vase.
Hydrangeas have a sticky substance in the stem and once they are cut the goo blocks the stem and it can’t suck up the water as needed. To keep hydrangeas fresh and make them last, if you are cutting them yourself, you must have a vase or bucket of water handy to put them in instantly when making the cuttings. Once you have your cuttings, take them inside and move the flowers from the bucket / vase to another container of HOT water and leave them for 10 minutes. This clears the inside of all that sticky stuff so the water will be able to travel up to the bloom. I have done this successfully and my hydrangeas did then last for days afterward.
If you are planning to use hydrangeas to decorate tables or as a centerpiece for a special event, be sure to cut them, and use the hot water method described above, as close to the event time as possible. If you have room in the refrigerator, keep them cool (in water) until needed.
If the bouquet is for decorating your home, be sure to change the water each day to keep the bouquet fresh.