The present invention relates to anti-microbial compositions that mayadvantageously beadded to vase water of cut flowers in order to prevent microbial growth,especially in vase watercontaining added cut flower nutrients and/or water uptake stimulants.One aspect of the invention relates to the use of an EC 1.1.3 oxidoreductaseas anantimicrobial additive for vase water of cut flowers.Another aspect of the invention concerns a method of putting cut flowers intovase water,said method comprising immersing the stems of one or more cut flowers intovase water andadding an antimicrobial composition containing an EC 1.1.3 oxidoreductase tothe vase waterbefore, after or at the same time as the cut flowers are immersed into thevase water