To significantly extend your sunflower bouquet's lifespan, select a sturdy vase and fill it with fresh, clean water. Place this vase in a cool, shaded area away from harmful direct sunlight, which can cause the blooms to wilt prematurely. Each day, diligently trim the stems of the sunflowers, removing any leaves that might be submerged, to enhance their absorption of water. Make sure to change the water in the vase every two days, thus preserving the bouquet's vibrancy. This method prevents bacterial growth, which could otherwise shorten the life of your flowers. Implement these steps consistently to enjoy the full beauty of your sunflower bouquet for as long as possible.