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Cheryl Hamaker, William H. Carlson, Royal D. Heins and Arthur C. Cameron

To determine the most effective lighting strategies for flower induction of long-day (LD) plants, 10 species of herbaceous perennials were chilled at 5C for 0 or 12 weeks and then forced at 20C under the following photoperiods: short day, 4-h night interruption (4-h NI), 7-h night interruption (7-h NI), 7-h day extension, 7-h predawn (7-h PD), and 24-h continuous light (24-h). All treatments consisted of a 9-h photoperiod of sunlight supplemented with 90 μmol·m–2 from HPS lamps. LD treatments were delivered by incandescent lights and induced flowering in obligate LD plants. Rate of flowering, height, and bud number at first flower varied among species and LD treatments. Although flowering was accelerated under 24-h and 7-h NI for most species, it was delayed under 24 h for Coreopsis verticillata `Moonbeam' and Campanula carpatica. For unchilled plants of most species, flowering was delayed under 7-h PD compared to other LD treatments. Chilling decreased time to flower and reduced differences between LD treatments. Coreopsis `Moonbeam' and C. Ianceolata `Early Sunrise' were shorter when grown under 4-h NI.

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Gary J. Keever and J. Raymond Kessler Jr.

In previous studies, night-interrupted lighting (NIL) promoted earlier flowering of summer-blooming herbaceous perennials grown under outdoor nursery conditions in the southeastern U.S. However, NIL promoted excessive plant height, thus reducing product quality. Our objective was to control plant height of Coreopsis grandiflora `Early Sunrise' (ES) and Rudbeckia fulgida `Goldsturm' (RG) grown under NIL with plant growth retardants (PGR) without offsetting earlier flowering promoted by NIL. Treatments under NIL were three rates of daminozide, daminozide plus chloromequat, flurprimidol, uniconazole, and NIL and natural controls. Plant height was reduced 3% to 38% in ES and 8% to 31% in RG and time to visible bud was unchanged by all PGR treatments compared to the NIL control. Time to visible bud was unchanged in RG by all PGR treatments and flurprimidol in ES, but the remaining PGR treatments increased time to visible bud compared to the NIL control in ES. Only ES plants treated with daminozide and daminozide plus chloromequat at the two highest rates and all rates of uniconazole were similar in height to the natural control. RG plant heights with the two highest rates of flurprimidol and uniconazole and the highest rate of daminozide plus chloromequat were less than the natural control; heights of plants in the remaining PGR treatments were similar to the natural control. Quality rating was unchanged in RG but was increased in ES by all PGR treatments compared to the NIL control.

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Paul Koreman, Art Cameron, Royal Heins and William Carlson

Previous research has shown that the photoperiod under which stock plants are grown has a significant effect on cutting production and rooting of several species of herbaceous perennials. Long-day (LD) treatment of stock plants promoted cutting production of certain LD perennials but reduced rooting. Cuttings from plants grown under short days rooted readily but few were produced. Stock plants were exposed to alternating photoperiods to determine if this treatment would yield many cuttings with high rooting potential. Coreopsis verticillata `Moonbeam' and Phlox paniculata `Eva Cullum' stock plants were given 4 weeks of 4-h night interruption (NI), while Sedum `Autumn Joy' stock plants were grown under 14-h days. After 4 weeks plants were given 0, 2, or 4 weeks of 10-h days. Cuttings were harvested and propagated under mist and three different photoperiods (10-h, 14-h, NI) for 4 weeks, after which rooting percentage and the number and length of roots produced by each cutting were measured. The results will be presented.

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Shi-Ying Wang, Royal D. Heins, William H. Carlson and Arthur C. Cameron

Four herbaceous perennial species, Delphinium grandiflorum `Blue Mirror', Hibiscus xhybrida `Disco Belle Mix', Salvia xsuperba `Blue Queen', and Veronica longifolia `Sunny Border Blue' were forced in a glass greenhouse at 15, 18, 21, 24, or 27°C under long days. Before being forced, all tested species except H. xhybrida were exposed to 5°C for 12 weeks. Increasing forcing temperature generally promoted visible bud and flowering. However, visible bud and flowering of D. grandiflorum `Blue Mirror' and flowering of V. longifolia `Sunny Border Blue' were delayed at 27°C. Although the tested species tended to have more flower buds, bigger flowers, and greater height at lower forcing temperatures, the effect of forcing temperature on those characteristics was species-dependent. Temperatures as low as 15°C decreased bud number and flower size of H. xhybrida `Disco Belle Mix'. The base temperature (Tb) and cumulative thermal time (CTT) necessary to complete the indicated developmental stage were calculated from a linear regression: 1/f = a + bT. Based this equation, days to flowering (or visible bud) at certain temperatures or the temperature required for flowering within a certain number of days can be predicted.

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Jeffery K. Iles and Nancy H. Agnew

Nine herbaceous perennial species were evaluated for use as flowering potted plants for late winter and early spring sales. Plugs of `King Edward' Achillea × Lewisii Ingw. (yarrow), Arabis sturii Mottet. (rockcress), `Alba' Armeria maritima (Mill.) Willd. (common thrift), `New Hybrid' Bergenia cordifolia (Haw.) Sternb. (bergenia), Chrysogonum virgianum L. (goldenstar), `War Bonnet' Dianthus × Allwoodii Hort. Allw. (Allwood pinks), Phlox × chattahoochee L. (Chattahoochee phlox), `Sentimental Blue' Platycodon grandiflorus (Jacq.) A. DC. (balloonflower), and Veronica L. × `Sunny Border Blue' (veronica) were established in 14-cm (0.8-liter) round plastic containers, grown for one season and covered with a thermoblanket for winter. Five plants of each species were transferred to a 21 ± 3C glasshouse for forcing under natural daylengths at six 10-day intervals beginning 1 Dec. 1993. Arabis sturii, Phlox × chattahoochee, Platycodon grandiflorus `Sentimental Blue', and Veronica × `Sunny Border Blue' flowered out of season without supplemental lighting. `Alba' Armeria maritima and Chrysogonum virginianum also flowered; however, their floral displays were less effective. `New Hybrid' Bergenia cordifolia did not flower and `King Edward' Achillea × Lewisii and `War Bonnet' Dianthus × Allwoodii only flowered sporadically, therefore, these perennials are not recommended for forcing out of season using our vernalization method.

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Erik S. Runkle, Royal D. Heins, Arthur C. Cameron and William H. Carlson

Six long-day species of herbaceous perennials were grown under six night-interruption (NI) photoperiod treatments to determine their relative effectiveness at inducing flowering. Photoperiods were 9-hour natural days with NI provided by incandescent lamps during the middle of the dark period for the following durations: 0.5, 1, 2, or 4 hours; 6 minutes on, 54 minutes off for 4 hours (10% or 6/54 cyclic lighting); or 6 minutes on, 24 minutes off for 4 hours (20% or 6/24 cyclic lighting). For five species, the experiment was repeated with more mature plants; for the sixth, Rudbeckia fulgida Ait. `Goldsturm', following a cold treatment of 8 weeks at 5 °C. The species generally showed a quantitative flowering response to the NI duration until a saturation duration was reached; as the length of the uninterrupted night break increased, flowering percentage, uniformity, and number and plant height increased and time to flower decreased. Minimum saturation durations of NI were 1 hour for Coreopsis grandiflora Hogg ex Sweet `Early Sunrise' and Hibiscus moscheutos L. `Disco Belle Mixed', 2 hours for Campanula carpatica Jacq. `Blue Clips' and Coreopsis verticillata L. `Moonbeam', and 4 hours for unchilled R. fulgida `Goldsturm'. Echinacea purpurea Moench `Bravado' flowered similarly across all lighting treatments. The 6/24 cyclic lighting regimen induced flowering comparable to that under a continual 4-hour NI for four of the six species and the cold-treated R. fulgida `Goldsturm'. Flowering under the 6/54 regimen was generally incomplete, nonuniform, and delayed compared to that under saturation duration treatments. Three of five species flowered earlier when more mature plants were placed under the NI treatments. Cold-treated R. fulgida `Goldsturm' flowered more rapidly than unchilled plants and the saturation duration of NI decreased to 1 hour.

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Raul I. Cabrera and Pedro Perdomo

Herbaceous perennials are the hottest item in the ornamental industry, yet relatively little is known about the most appropriate management and cultural practices for many of these species. The response of selected perennials to controlled-release fertilizer (CRF) rates was evaluated in this study. Liners of Coreopsis `Early Sunrise' and `Zagreb', Astilbe `Bridal veil', Hemerocallis `Stelladoro', Phlox `Franz Shubert', and Rudbeckia `Goldstrum' were transplanted to 5.7-L pots filled with a 2 peat: 1 perlite (v/v) medium amended with dolomite and Micromax (2 and 0.6 kg·m-3, respectively). Plants were topdressed with Osmocote 18N-2.7P-10K at rates of 0, 1.8, 3.6, 5.3, 7.1 (industry standard) and 8.9 kg·m-3, and grown over a 3-month period. Plant biomass and quality ratings (including chlorophyll levels) followed an asymptotic behavior with CRF applications for Coreosis `Early Sunrise' and Astilbe `Bridal veil', leveling at ≈1.8 kg·m-3. The rest of the species showed increases in plant growth and quality with CRF rates of 1.8-3.6 kg·m-3, followed by sharp, and significant, reductions at higher CRF rates. Observations of optimum growth and quality at CRF rates 1/2 to 3/4 below commercial recommendations were partially attributed to the use a peat medium, with relatively higher nutrient holding characteristics in relation to the more common pine bark mixes. This observation was confirmed the following season, where plants grown in a 4 pine bark: 1 sand medium (v/v) required higher CRF rates to have similar growth and quality responses to those grown in a 4 peat: 1 bark: 1 sand medium (v/v).

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Christina M. Twardowski, Jaime L. Crocker, John R. Freeborn and Holly L. Scoggins

Many perennial growers maintain their own stock plants to produce cuttings for rooting as a cost-effective alternative to ordering in rooted liners. However, a number of widely grown herbaceous perennial species are difficult to propagate; stock

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Marie-Anne Boivin, Marie-Pierre Lamy, André Gosselin and Blanche Dansereau

A green roof system was installed on an existing 35-year-old building. The purpose of the study was to evaluate the effect of three substrate depths on low-temperature injury of six herbaceous perennials: bugleweed (Ajuga reptans), sandwort (Arenaria verna `Aurea'), sea pink (Armeria maritima), whitlow grass (Draba aizoides), creeping baby's breath (Gypsophila repens), and stonecrop (Sedum xhybridum). Plants in 4-inch (9-cm) pots were transplanted into three substrate depths: 2, 4, and 6 inches (5, 10, and 15 cm) and evaluated over a 3-year period. The analysis of the results showed that the species have different winter hardiness, therefore some species were subject to more freezing injury than others. Stonecrop had significantly more damage at 2-inch than 4- or 6-inch depths during the two winters. Bugleweed and creeping baby's breath showed more damage at 2 inches in 1996-97, not in 1995-96. Substrate temperatures were measured from Oct. 1995 to May 1997. Low temperature injury was more pronounced at 2 inch than at 4 or 6 inch depths. Minimum daily temperature and temperature variations measured in fall and spring of these 2 years were also higher at 4- and 6-inch depths.

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Erik S. Runkle, Royal D. Heins, Arthur C. Cameron and William H. Carlson

Six obligate long-day species of herbaceous perennials were grown under six night-interruption treatments to determine their relative effectiveness at inducing flowering. Photoperiods were 9 hours natural days with night interruptions provided by incandescent lamps during the middle of the dark period for the following durations: 0.5, 1, 2, or 4 hours; 6 minutes on, 54 minutes off for 4 hours (10% cyclic lighting); or 6 minutes on, 24 minutes off for 4 hours (20% cyclic lighting). Response to night interruptions varied by species, but five of the six species flowered most rapidly and uniformly under 4-hour night interruption. Few or no Campanula carpatica `Blue Clips', Rudbeckia fulgida `Goldsturm', or Hibiscus ×hybrida `Disco Belle Mixed' plants flowered with 1 hour or less of continuous night-break lighting. All Coreopsis ×grandiflora `Early Sunrise' flowered, but flowering was hastened as the duration of night interruption increased. Echinacea purpurea `Bravado' flowered similarly across all treatments. In general, the effectiveness of the night-interruption treatments at inducing flowering was 4 hours > 2 hours > 20% cyclic > 1 hour > 10% cyclic > 0.5 hour.