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Amy M. Fay, Steven M. Still and Mark A. Bennett

Germination trials of three seedlots were conducted over a temperature gradient for 14 days to determine the optimal germination temperature for the Black-eyed Susan (Rudbeckia fulgida Ait.). The optimal germination temperature for R. fulgida seeds was 30 ± 1C. All three seedlots began germination (radicle emergence) on the second day at 30.2C. By day four, all seedlots sur-passed 50% germination, with three seedlots germinating 53%, 52%, and 73%. Mean germination percentages were higher between 28.3 and 32.6C than at temperatures above or below this range. Significantly higher germination percentages and enhanced germination rates attained at the elevated temperatures may save time, cut production costs, and decrease exposure to detrimental pre-emergent pathogenic fungi.

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

To determine the flowering requirements of Rudbeckia fulgida Ait. `Goldsturm', plants were grown under 9-hour photoperiods until maturity, then forced at 20 °C under one of seven photoperiods following 0 or 15 weeks of 5 °C. Photoperiods consisted of a 9-hour day that was extended with incandescent lamps to 10, 12, 13, 14, 16, or 24 hours; an additional treatment was a 9-hour day with a 4-hour night interruption (NI). Noncooled `Goldsturm' remained vegetative under photoperiods ≤13 hours, and essentially all plants flowered under photoperiods ≥14 hours or with a 4-hour NI. Flowering percentages for cooled plants were 6, 56, or ≥84 under 10-, 12-, or ≥13-hour daylengths and NI, respectively. Critical photoperiods were ≈14 or 13 hours for noncooled or cooled plants, respectively, and base photoperiods shifted from 13 to 14 hours before cold treatment to 10 to 12 hours following cold treatment. Within cold treatments, plants under photoperiods ≥14 hours or NI reached visible inflorescence and flowered at the same time and developed the same number of inflorescences. Fifteen weeks of cold hastened flowering by 25 to 30 days and reduced nodes developed before the first inflorescence by 28% to 37%. Cold treatment provided little or no improvement in other measured characteristics, such as flowering percentage and uniformity, flower number, plant height, and vigor.

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Amy M. Fay, Mark A. Bennett and Steven M. Still

Low-vigor seeds of black-eyed Susan (Rudbeckia fulgida Ait.) primed in aerated -1.3 MPa KNO3 for 7 days at 30C in darkness had double the total germination percentage at 30C and one-half the mean time of germination as nonprimed seeds. Priming the seeds in polyethylene glycol rather than KNO3 generally resulted in lower total germination percentage and longer mean time of germination. Osmotic priming increased total germination percentage and germination rate of seeds germinated at 21.9 to 32.2C, but the priming benefit on total germination percentage was greater at ≤27.6C. Total germination percentage of primed and nonprimed seeds was highest at 28.8 to 32.2C.

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Mei Yuan, William H. Carlson, Royal D. Heins and Arthur C. Cameron

Most plants have a postgermination juvenile phase in which flower induction will not occur. Some species require a cold period for flower induction and will not respond to the cold treatments during the juvenile phase. We determined juvenile phases of Coreopsis grandiflora `Sunray', Gaillardia grandiflora `Goblin', Heuchera sanguinea `Bressingham', and Rudbeckia fulgida `Goldsturm'. Plants were exposed to 5C for 0, 10, or 15 weeks when Coreopsis had 0, 2, 4, 6, 8, or 10 leaves (>1 cm); Gallardia, 4, 8, 12, or 16 leaves; Heuchera, 8, 12, 16, or 20 leaves; Rudbeckia, 5, 10, 15, or 20 leaves. Plants were grown under a 4-h night interruption lighting (LD) or under a 9-h photoperiod (SD) after cold treatments. Based on time to flower and final leaf count, the juvenility of Coreopsis, Gaillardia, Heuchera, and Rudbeckia ended when they had about 6, 10, 12, and 15 leaves, respectively. Cold treatments were necessary for flower induction of Coreopsis and Heuchera and they increased the flowering percentage of Gaillardia and Rudbeckia. Heuhera was a day-neutral plant, Rudbeckia was on obligate LD plant, and Gaillardia and Coreopsis were quantitative LD plants.

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Mei Yuan, William H. Carlson, Royal D. Heins and Arthur C. Cameron

Scheduling crops to flower on specific dates requires a knowledge of the relationship between temperature and time to flower. Our objective was to quantify the effect of temperature on time to flower and plant appearance of four herbaceous perennials. Field-grown, bare-root Coreopsis grandiflora (Hogg ex Sweet.) `Sunray', Gaillardia ×grandiflora (Van Houtte) `Goblin', and Rudbeckia fulgida (Ait.) `Goldsturm', and tissue culture—propagated Leucanthemum ×superbum (Bergman ex J. Ingram) `Snowcap' plants were exposed to 5 °C for 10 weeks and then grown in greenhouse sections set at 15, 18, 21, 24, or 27 °C under 4-hour night-interruption lighting until plants reached anthesis. Days to visible bud (VB), days to anthesis (FLW), and days from VB to FLW decreased as temperature increased. The rate of progress toward FLW increased linearly with temperature, and base temperatures and degree-days of each developmental stage were calculated. For Coreopsis, Leucanthemum, and Rudbeckia, flower size, flower-bud number, and plant height decreased as temperature increased from 15 to 26 °C.

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Mei Yuan, William H. Carlson, Royal D. Heins and Arthur C. Cameron

Scheduling crops to flower for specific dates requires a knowledge of the relationship between temperature and time to flower. Our objective was to determine the relationship between temperature and time to flower of four herbaceous perennials. Field-grown, bare-root Coreopsis grandiflora `Sunray', Gaillardia grandiflora `Goblin', Rudbeckia fulgida `Goldsturm', and tissue culture-propagated Chrysanthemum superbum `Snow Cap' were exposed to 5C for 10 weeks. They were grown at 15, 18, 21, 24 or 27C under 4-h night interruption lighting. Time to visible bud (VB) and first flower (FLW) were recorded. Days to VB, days to FLW, and days from VB to FLW decreased as temperature increased. Time to flower at 15C was 70, 64, 96, and 54 days and 24, 39, 48, and 36 days at 27C for Coreopsis, Gaillardia, Rudbeckia, and Chrysanthemum, respectively. The 27C temperature apparently caused devernalization on Coreopsis because only 40% of the plants flowered. The effects of temperature on flower size, flower bud number, and plant height also are presented.

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Helen H. Tyler and Stuart L. Warren

An experiment with a factorial treatment combination in a split plot design with five single plant replications was conducted to evaluate the effects of five rates of fertilizer addition and two irrigation volumes on plant growth in a composted turkey-litter-amended pine bark substrate. Main plots were daily applications of 600 or 900 ml/3.8-L container. Subplots were either 0, 1.0, 2.0, 3.0, or 4.0 g N additions (Osmocote High H 24N–1.7P–5.8K) per container topdressed on a substrate composed of pine bark amended with 8% (by volume) composted turkey litter. No additional amendments were made to the compost amended substrates. An additional “industry control” treatment consisted of an 8 pine bark: 1 sand (by volume) substrate amended with 3.0 kg/m3 dolomitic limestone and 0.9 kg/m3 Micromax and topdressed with 3.5 g N (Osmocote High N) per container. After 134 days, Cotoneaster dammeri `Skogholm' and Rudbeckia fulgida `Goldsturm' plants were harvested and shoot and root (cotoneaster only) dry weights were determined. Cotoneaster shoot and root dry weights and rudbeckia shoot dry weight increased linearly as N rate increased from 0 to 4.0 g N. Irrigation volume did not affect cotoneaster shoot or root dry weights. Rudbeckia shoot dry weight was 18% greater with 900 ml than with 600 ml of irrigation. Rudbeckia growth in compost amended substrate was greater than in the industry control when topdressed with ≥1.0 g N. Shoot growth of cotoneaster in the industry control substrate and compost amended substrate with ≥ 3.0 g N applied was similar.

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Yan Chen, Regina P. Bracy, Allen D. Owings and Joey P. Quebedeaux

Use of controlled-release fertilizers (CRF) has been recommended to the landscape service industry as a best management practice for establishing landscape plants. However, application practices vary considerably among professionals and recommendations are lacking for the appropriate type (tablet vs. granular), application rate, and timing of CRF to establish herbaceous perennials. In this study, cigar plant (Cuphea ignea), daylily (Hemerocallis ‘Stella de Oro’), gaura (Gaura lindheimeri ‘Siskiyou Pink’), lantana (Lantana camara ‘New Gold’), mexican heather (Cuphea hyssopifolia), purple coneflower (Echinacea purpurea), and rudbeckia (Rudbeckia fulgida ‘Goldsturm’) were fertilized with granular CRF (GF) 15N–3.9P–10K (8 to 9 month) at 0, 1, 2, or 4 lb/1000 ft2 nitrogen (N) at transplant (no fertilization, GF1, GF2, and GF4, respectively), a split application of GF with 1 lb/1000 ft2 N applied at transplant and 1 lb/1000 ft2 N applied 5-months later (GF2-split), or tablet CRF 16N–3.5P–10K (8 to 9 months) at two tablets per plant (7.5 g) at transplant (TF2). Plant size and visual quality (VQ) at 5 months after transplant (MAT) were improved by fertilization for all perennials except ‘Stella de Oro’ daylily. Compared to GF2, GF4 improved the growth of perennials of larger size and greater biomass production (i.e., cigar plant), but did not further improve their VQ. All perennials grown with TF2 had similar size and quality as those grown with GF2 at 5 MAT. At 15 MAT, no difference was found among fertilizer treatments for surviving perennials except cigar plant. Split application (GF2-split) did not improve overwinter survival or second-year plant growth and quality for most species when compared with GF2. On the basis of these results, we recommend applying two tablets (7.5 g) of 16N–3.5P–10K per plant at transplant to establish the perennials tested in this study.

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H.T. Kraus, S.L. Warren, G.J. Bjorkquist, A.W. Lowder, C.M. Tchir and K.N. Walton

data management for all experiments. Seedlings of Rudbeckia fulgida var. sullivantii Ait. ‘Goldsturm’ (rudbeckia) and Hibiscus moscheutos L. (hibiscus) grown in 16.39-cm 3 containers were transferred into 3.8-L black plastic containers filled

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Helen T. Kraus, Stuart L. Warren and Charles E. Anderson

Five ratios of NH4+: NO3-(100:0, 75:25, 50:50, 25:75, and 0:100) were evaluated for impact on growth of Cotoneaster dammeri Schneid. `Skogholm' (cotoneaster), a woody ornamental shrub, and Rudbeckia fulgida Ait. `Goldsturm' (rudbeckia), an herbaceous perennial. Nitrate alone decreased dry weight and leaf area of cotoneaster and rudbeckia compared with mixtures of NH4+ and NO3- and NH4+ alone. Additionally, NO3- alone suppressed accumulation of cationic nutrients and N in cotoneaster, while mixes of NH4+ and NO3- enhanced accumulation of nutrients in roots and shoots of rudbeckia compared with solutions containing either NH4+ or NO3- alone. The steles of roots of cotoneaster and rudbeckia contained more secondary xylem with larger tracheary elements with a mix of 25 NH4+: 75 NO3- than with NO3- alone.