Cut Poinsettia stems exude a milky sap in the water. We like to remove all the foliage that will be below the water line in the vase, give the stem a sharp angled cut and place it in a vase of cool water. We let it sit for an hour or two to get most of the milky water out of the stem. Then, you are ready to arrange with the stem. When moving the Poinsettia to its “presentation” vase, make sure you move the stem quickly into the new water without re-cutting the stem. This way, the stem won’t seal up before it’s in the new vase and most of the milky sap will be gone. It’s a good idea in all vases to change the water every 2-3 days, but you may want to change it more often to keep the water from looking cloudy from any more sap that comes out of these stems.