Tithonia Flower Mexican Sunflower Plant care Growing Tithonia Flower Summer Flowers Hydrogen Peroxide: A Gardener's Secret Weapon! Revive Sick Plants: Mix 1 part hydrogen peroxide with 2 parts water for root rot relief. Prevent Infections: Lightly spray on leaves to disinfect Pest plant Water dropwort Department of Environment, Water and Adding hydrogen peroxide to your watering routine helps your houseplants and keeps root rot away.