As is well known, hyacinths grow much faster with longer cooling, and require more PGR. For mid-Easter flowering, most cultivars would need 2-2.5 mg/pot. For late Easters, even higher rates are probably needed (probably 2.5 -3 mg/pot).
Topflor comes as a 0.38% active ingredient liq uid (3,800 mg/liter). Assuming a cost of $113/ liter container, the chemical cost of Topflor comes to $113/3,800 mg = $0.0297 per mg a.i. Thus, the chemical cost of a 1, 2, or 3 mg/pot drench is 3, 6, or 9 cents (U.S). per pot, re spectively. These costs are probably too high for 4” pots, but are more reasonable for 6” or larger containers.
Specific use rates must always be determined by each grower under local conditions. Growth temperature, soil, bulb size and many other factors all affect plant response to any growth regulator.
Conclusions
Pre-plant Topflor dips show excellent promise for hyacinth growth regulation. A starting point for commercial trials would be to dip hyacinth bulbs into 20 ppm Topflor for 10-30 minutes (See Table 3). This concentration works well across a number of cultivars and cooling dura tions, and should give good results in most cases. A slight (1-4 day) flowering delay might be observed, but this is potentially a benefit as it could be used to extend marketing/retail dis play time periods. Shorter stems and more compact leaf growth are also to be expected in the postharvest phase. For very late forcing (long cold durations), higher concentrations (up to 40 ppm) and longer dips (10-30 min utes) might be needed, again per cultivar.
In-greenhouse Topflor drenches are also very effective, but are overall more expensive and somewhat less effective than pre-plant dips. Suggested rates are in Table 4. It would be interesting to evaluate Topflor drenches before cooling to see whether this might lead to a more robust treatment. Such studies are planned for the 2011 forcing season.