Pot daffodils bring color to our homes in the depth of winter where their mainly yellow and white flowers are enjoyed for their subtle fragrance and elegance. Bulbs for forcing are produced mainly in England and Holland and are shipped worldwide for greenhouse forcing. The main cultivar is the dwarf 'Tete-a-Tete' which is especially attractive in 4" pots. Other cultivars can be grown in greenhouses or fields and harvested as a cut flower.
Over the past few years we have conducted extensive trials with a number of daffodil cultivars, especially in the context of developing better postharvest height control measures. As with hyacinths, Florel (ethephon; an ethylene-releasing growth regulator), has been used as the main height control technique in daffodils. Depending on the cultivar and time of forcing, foliar sprays of 500-2,000 ppm Florel (one or two sprays) are recommended.
Sometimes, however, Florel is not fully effective on daffodils, 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 daffodils, and has proven useful as a pre-plant bulb dip, or potentially as an at-planting drench, or a more traditional in-greenhouse drench 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 (16 and 17 weeks). Plants are generally grown 2-3 bulbs per 6" pot, cooled for 16 or 17 weeks, then forced at a temperature of 63F nights (17C) and 63-72F days (17-20C).
Our typical Topflor pre-plant dip treatments have been 10 or 25 ppm Topflor for 5, 10 or 30 minutes. Drench treatments have been 1, 2, 3 mg Topflor or Bonzi per 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" link 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.