Why a sharp knife?
A knife is recommended!
A sharp knife will allow you to cleanly cut just about any flower stem. A scissors or a clippers maybe more comfortable to use but can crush the tiny vessels that transport the water from the bottom of the stem to the bloom.
A scissors can be used to cut excess foliage from the stem (hydrangeas for example) and a soft cloth or rose stripper can be used to remove foliage and thorns from rose stems. A sharp clippers or pruner can be used to cut heavy wooded stems such as flowering branches, viburnum or curly willow.
See our Florist Tools section for knives and rose strippers.