Pot hyacinths are enjoyed for their color, fragrance and elegance. Bulbs are produced almost exclusively in Holland and are shipped worldwide for greenhouse forcing as a winter to spring pot plant or cut flower. In Europe, potted hyacinths are also available in late fall as a result of special bulb production, temperature treatment, and forcing techniques. While such potential also exists for North America, to date the late fall market for hyacinths has not been developed.
Over the past few years we have conducted extensive trials with a number of hyacinth cultivars, especially in the context of developing better height control measures. Historically, Florel (ethephon; an ethylene releasing growth regulator), has been used as the main height control technique in hyacinths. Depending on the cultivar and moment in the season, foliar sprays of 500-2,000 ppm Florel (one or two sprays) are recommended.
However, some growers report variable effects with Florel on hyacinths and this has stimulated our interest in developing production information on other PGRs, mainly those that work by reducing gibberellin production in the plant (and, therefore, leading to shorter plants). In the last few years, Topflor (flurprimidol, from SePRO Corp.) has emerged as an excellent product for use on hyacinths, and has proven useful as a pre-plant bulb dip, or as an in-greenhouse drench very shortly after forcing begins.
In our trials, we have evaluated Topflor as a pre-plant dip, or as in-greenhouse drenches, at two different cold durations (15 and 18 weeks). Plants (generally 17/18 cm bulbs) are grown 1 bulb per 4" pot, cooled for 15 or 18 weeks, then forced at a temperature of 63F nights (17C) and 63-72F days (17-20C). While 18 weeks is more cold than needed for proper flowering, we have chosen to evaluate it, since it is relatively common in North American forcing that late season hyacinths are over-cooled. This is because greenhouses typically grow a wide variety of crops, and bulb planting in the fall is often shoehorned into the ongoing greenhouse work schedule.
Our typical Topflor pre-plant dip treatments have been 20 or 40 ppm Topflor for 10 to 60 minutes. Drench treatments have been 1, 2, 3 or 4 mg Topflor/pot (16, 33, 50, or 66 ppm given as a 2 ounce drench per 4" pot).
For each cultivar, basic information on characteristics, cold week recommendations and PGR needs are given. Clicking on the "More images and information" links on each cultivar page will bring up a .pdf file for each cultivar with images per year of the effects of cold weeks and Topflor treatments.