Use flowers that have just opened, include buds as well. Cut flowers should be picked early in the morning or in the evening. Stems are apt to wilt quickly if cut in mid day when the plants are losing water.
Whenever possible cut flowers just above a side branch on which another flower is forming. Make the cut with a clean, sharp knife or shears. Strip off some of the leaves and plunge the stems in warm water as quickly as possible.
Maintaining Cut Flowers
Most commercial preservatives do help cut flowers. Along with quick energy sugar, they also provide other useful substances; a bacteria-inhibiting material to control the spread of those organisms that clog the ends of the stems; an acidic material to lower the alkalinity of the water and to reduce the growth of microorganisms; metallic salts to maintain color in the petals; and respiratory inhibitors to cut down the flowers metabolic rate.
Nothing helps keep cut flowers more than a scrupulously clean environment. Make sure the container you use is free of any dirt left from a previous flower arrangement, and give the flowers fresh water at 100-110¿F, not cold - every day.