How to Trim Dead Flowers From Stock Plants

Wait until the flowers on your stock plant begin to wilt and die. The flowers are on a single stalk and will begin to die from the bottom up. As they die completely, the flowers will naturally drop off.
Trim the flower stalk from the stock plant with sharp hand pruners or snips.
Cut the stalk as close to the base of the stock plant as possible. This directs the energy of the plant to producing a new flowering stalk instead of trying to maintain the dying flower stalk.