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Cutting your flowers earlier in the day when it's cool will ensure that the flower has stored carbohydrates, which are required to keep them alive.  Keep a bucket of water with you and make sure to transfer them immediately after cutting them. Flowers need a constant stream of food to flourish, and being left out of the water causes them to dry up.  Flowers should be cut at varying maturity levels depending on the type of flower. Daffodils, roses, irises and gladiolas should be cut in the bud stage, while delphiniums, marigolds, dianthus flowers should be open before cutting.  Use a plastic bucket or pail. Metal can throw the flower's pH balance and reduce its lifespan. Refrigeration at 35°F (1.5°C) can triple the lifespan of freshly cut flowers in your house. Doing this before you transfer them to a vase with water slows down water loss, respiration, and development. Your flowers will require less water and die slower if you put them in the fridge.  Slowing down the flower's development will allow it to remain in the flowering stage for a longer period of time before wilting and dying. You can also pop your flowers in the refrigerator when you are going to sleep to help preserve them for a longer time. Trim one inch from the bottom of the stem at a 45-degree angle using durable gardening tools like shears or clippers. Water bubbles can get trapped on the end of a flower's stem which will prevent it from absorbing water. Keeping your flowers recut will ensure that their water absorption levels remain steady.  Flowers like the sunflower develop sap on the end of their stems after some time. You can remedy this by pouring boiling water on the end of the stems for 20 seconds.  Do not crush the stem, as this can damage the flower internally and inhibit water absorption.

Summary:
Cut your flowers in the morning. Place freshly cut flowers in your refrigerator for six hours. Recut the stems on your flowers every three days.