Increase cut flowers’ longevity Freshly cut flowers will stay fresh longer if you add 1/4 teaspoon bleach per quart (1 liter) of vase water. Another popular recipe calls for 3 drops bleach and 1 teaspoon sugar in 1 quart (1 liter) water. This will also keep the water from getting cloudy and inhibit the growth of bacteria.
Is there any proof? I would imagine bleach would be toxic to flowers.