Inadvertent drift from a PGR application can damage sensitive species. Drift from an application of Florel to overhead baskets caused stunting and delayed flowering (right). The unaffected flat of the same cultivar is pictured to the left.
For more information on using plant growth regulators see:
Message posted March 19, 2007
Fact Sheets: Growth Regulators for Bedding Plants
Subirrigating Seed Geraniums with Bonzi
2007-2008 New England Floriculture Guide: About Growth Regulators (PDF)