To ensure the longevity and beauty of your arrangement of white mixed flowers in a flower box, here are some care guidelines to follow:

1. **Watering**: Check the water level in the flower box regularly, ensuring that the floral foam or sponge at the base of the arrangement remains hydrated. Add water as needed to keep the foam moist, without soaking the flowers' stems.

2. **Trimming**: Trim the stems of the flowers every few days, cutting them at an angle to facilitate water absorption. Remove any wilted or dead flowers promptly to maintain the overall appearance of the arrangement.

3. **Placement**: Position the flower box in a cool area away from direct sunlight, heat sources, and drafts. Exposure to excessive heat or cold can accelerate wilting.

4. **Cleaning**: Remove any fallen petals or debris from the flower box to prevent bacterial growth, which can hasten the deterioration of the flowers. Gently wipe the leaves and petals with a damp cloth if they accumulate dust.

5. **Misting**: Lightly mist the flowers with water using a spray bottle, especially if the environment is dry. This can help to keep the flowers hydrated and prolong their freshness.

6. **Avoiding Ethylene**: Keep the arrangement away from ripening fruits and vegetables, as they emit ethylene gas, which can cause the flowers to deteriorate more rapidly.

7. **Enjoyment**: Take time to appreciate and enjoy the beauty of your white mixed flower arrangement. With proper care, it will continue to adorn your space with elegance.

By following these care instructions diligently, you can extend the lifespan of your white mixed flower arrangement and preserve its aesthetic appeal for as long as possible.