To maintain the freshness and beauty of your arrangement of 20 red roses in a glass vase, follow these flower care tips:

1. **Trimming Stems**: Upon receiving the roses, trim the stems at a diagonal angle using sharp scissors. This allows for better water absorption.

2. **Clean Vase**: Ensure the glass vase is clean before arranging the roses. Fill it with lukewarm water, about halfway full.

3. **Removing Leaves**: Remove any leaves that will be submerged in water to prevent bacterial growth. This keeps the water clean and clear.

4. **Water Level**: Check the water level daily and top up as needed to keep the stems submerged. Change the water every 2-3 days to maintain freshness.

5. **Location**: Place the vase in a cool spot away from direct sunlight and heat sources. Avoid placing them near fruits or vegetables, as they emit ethylene gas which can hasten wilting.

6. **Pruning**: Remove any wilted or dead petals and leaves from the arrangement to keep it looking fresh.

7. **Misting**: Occasionally mist the petals with clean water to hydrate them and maintain their appearance.

8. **Enjoyment**: Finally, enjoy the beauty and fragrance of your red rose arrangement, and remember to appreciate their elegance and charm.

By following these care tips, your arrangement of 20 red roses will remain fresh and vibrant for an extended period, adding a touch of beauty to your space.