The entire process of keeping cut flowers depends on keeping as much water inside the flower and stem as is possible. So if in the very beginning of the process you use a dull scissors or knife to cut the flower in the yard, you hurt the stem's ability to take up water. So use a sharp knife or sharp pruners when you cut your flowers out in the yard. Cut the stems at an angle, and don't ask me why because I don't know; all the experts say cut at an angle and so I follow that rule. Try to cut flowers in the early morning, while they are still full of water and covered with dew. Flowers cut in the evening have lost lots of moisture from the heat of the day.
Carry a bucket of water right along with you, so the stem is exposed to air for just a second or two; we really go to a lot of trouble to keep those stems pulling in water. Keep those stems in the water in the bucket.