The use of a graphical tracking system is highly recommended for poinsettias. With similar day and night temperature setpoints, the need for chemical height control is minimal for many varieties. When day temperatures are more than 5°F higher than night temperatures, a Cycocel spray at 750 to 1,000 ppm one to four times after pinching is sufficient in Northern climates to control stem extension.
When day temperatures are greater than 80°F and night temperatures are greater than 70°F, spray a tank mix of Cycocel at 1,000 ppm plus B-Nine at 1,500 ppm one to three times, one to four weeks after pinching. Bonzi sprays can also be used at 5 to 10 ppm under these warm growing conditions. Proper growth regulation before and after the pinch, combined with high light conditions are critical to avoid early internode stretch and to build a sturdy plant. Avoid B-Nine and Bonzi sprays after flower initiation.
Florel. Florel plant growth regulator (PGR) applied at 500 ppm three to five days before and five to seven days after pinching leads to shorter internodes, more even branching, reduced stem breakage and a rounder finished plant. For optimum results, add CapSil, moisten the media, treat plants early in the morning and check for a good root system.
Mid-season Ultra-low-rate Bonzi Drench. Low-rate Bonzi drenches provides additional growth control without delaying color, distorting bracts or significantly reducing the bract size. The recommended drench rate after flower initiation and prior to 50 percent color is 0.05 to 0.1 ppm. For traditional late-season growth control, drench with Bonzi in the north at ¼ to ½ ppm (0.75 to 1.5 ounces/100 gallons) and in the south at ½ to 1 ppm (1.5 to 3 ounces/100 gallons). This can be done when the plants are about ½ to 1 inch below the desired height and/or one to two weeks (up to three weeks in the South) before shipping.
Gibberellic Acid (GA). For a moderate increase of internode length, spray GA at 2 to 3 ppm using ProGibb 4 percent (4 milliliters/10 gal.) or Fascination, ideally in the first part of October. The maximum elongation occurs about one to two weeks after application. Two to 4 inches of growth are possible within that time frame, depending on variety and temperature. Spraying Fascination at 2 to 3 ppm with CapSil about two weeks before finishing improves the color of white varieties and can be used to increase bract size if needed.