When you buy cut tulips and put them into water, they keep growing (because they’re hardy little things). The problem is that as they grow, they get top-heavy and their weedy little stems can’t support their full, glorious heads. To slow down this process, just put a little bit of water in the vase (5 cm or less) and change the water every day. This should keep them looking fresh, without them drooping too quickly. Also, keep them out of direct sunlight.