Roses are woody-stemmed flowers that do not require cauterisation unless the rose stem is leaking sap. Much like cauterising a wound, rose stems can be cauterised with a flame to stop the bleeding out of sap. Cauterising flower stems is a way of keeping fresh-cut flowers fresh longer. The burning of the stem creates a scab over the cut end of the flower that prevents vital nutrients from escaping.
Submerge the stem under water. Cut the rose stem at a 45-degree angle under the water with a sharp knife or pruners. This discourages the formation of air bubbles in the stem. When air bubbles are present in the stem, they create a blockade that prevents water and nutrients from reaching the flower, causing it to fade sooner.
Light a candle. Hold the cut end of the stem over the candle flame until the stem just starts to turn black. The flame singes the cut end of the stem to prevent sap and nutrients from escaping.
Mix flower preservative with lukewarm water in a vase. Place the cut stem into a vase of water. The rose absorbs water through the cell walls of the stem to keep the flower looking fresh.
Hydrangea, butterfly weed, iris, columbine and poppies all exude sap and benefit from being cauterised before being added to an arrangement.
Don't hold the stem in the flame too long or it will burn.