My Benary Giant Zinnia stems are collapsing and turning brown almost immediately in the vase. Does anyone else have this problem? I've grown zinnias for years, although never Benary Giants, and I've never had this problem before. I harvest the stems and put immediately into water and then condition several hours in the house before arranging. Many times they don't even last two days and the Lime Green Benarys are turning brown around the edges within a day or so. I just use plain water and our water is not that good here..........should I be using a preservative? I grow as organically as possible, but this year, I am having a crisis of confidence. I do sell at the Farmers Market so this is becoming kind of embarrassing. Any tips wold be appreciated.