1.) Place flowers in water as soon as possible. Once the stems of flowers have been cut, you have removed their life support system.
2.) Fill a plastic bucket a third to half way with warm water. Warm water should be used as flowers take up warm water more readily than cold. Its preferable to add preservative to the water. (The use of preservatives is explained further on). Flowers only drink through the ends of the stems and not through the sides of the stems, and for this reason buckets should not be filled right up to the top with water, as foliage left on stems below the water line will rot and pollute the water. This will feed bacteria and the flowers will die more quickly. The foliage of marigolds, chrysanthemums, stock and daisies send off a particularly strong odor when left standing under water over a period of time.
3.) Take the bucket of water into the garden with you. Use a sharp pair of secateurs and cut the flower stems on an angle – a slanted cut allows a better intake of water. Remove all foliage from the lower portion of the stems which would stand under the water line. Place the flowers immediately in the water.
4.) Avoid overcrowding flowers. Allow enough air to circulate between each flower. Too many flowers crowded together in a bucket may cause the petals to become squashed and bruised. Place the bucket in a cool dark place and allow the flowers to have a long drink before being arranged. When picking short-stemmed flowers, use a smaller container.
5.) Allow flowers to have a good drink for four to five hours, preferably overnight before arranging. This step is called conditioning. It allows the stems to fill up with water and the flowers will become crisp. These flowers will last twice as long as those that have not been conditioned properly.
6.) Use a flower preservative to destroy bacteria in the water. Flower preservatives are available in garden centres or supermarkets. Another alternative is to use a capful of household bleach in the water. If a preservative is not used, the water needs to be changed and the stems cut on an angle daily. If a preservative is used, the stems do not require recutting and water needs changing only about twice a week. Flowers like freesias, spray carnations and liliums have lots of buds. By using a preservative in the water, it helps develop the buds to open.
Tips mentioned above are compliments of wikiHow