This is how you do it:
Choose a rose that you like, remove all leaves from the stem and cut the head of the rose diagonally (about three centimetres from the flower). If the flower still looks nice, you can put it in a small vase. Grab the potato and drill a hole in the potato, large enough so that the stem of the rose fits without wobbling.
Cover the bottom of the pot with 5 centimetres of potting soil and place the potato on top of it. Now fill the rest of the pot with soil. Cut off the bottom of the bottle and carefully place it over the rose stalk as a sort of bell jar. Give the rose water from time to time (around the bottle) and watch your roses bloom like never before!