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You should cut the stems at an angle while submerged in either a basin of water or running water. Exposing the cut end of your flower to open air can be damaging, especially since this is one of the points when flower tissue is most hungry for water. Additionally, you should try to cut your flowers in the early morning or late evening, as these are the best times to cut flowers. If you notice that your flowers, when cut, exude a milky liquid, you can prolong the life of these with a quick boil in water. Soak the bottom two inches of your cut stems in boiling water for ten seconds before putting into a vase. Two common flowers that can benefit from boiling are poinsettias and poppies. If your flowers have leaves all the way down the stem, these can rot in your water and cause mold to grow. Remove all leaves on your stems that will be below the waterline. You can determine whether your water is hard or not by noting mineral deposits on facets and kettles. These will often look like a white, scaly film when dry. If this is the case at your home, your plants will fare better with demineralized water, to which you can add vase preservative. Demineralized water is sold at most supermarkets and should be used in your vase solutions as well if you have hard water. Your homemade plant preservative will likely work even more effectively than commercial recipes, but these are an easy to use and inexpensive substitute if you lack the ingredients for the DIY recipe. Many times, a commercial preservative requires only a clean vase and warm water, though you should always follow the directions on the packet.
Cut your flowers under water. Boil the stems of flowers with sap. Prune leaves below the water line. Use demineralized water if you have hard water. Add a commercial vase preservative to your water.