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Brian Whipker and P. Allen Hammer

Acidification of the irrigation water with phosphoric acid is a common practice to avoid nutrient deficiencies/toxicities from alkaline root media. It has been suggested high phosphorus levels could cause phosphorus toxicity.

Euphorbia pulcherrima Willd. cultivars Supjibi and Celebrate 2 cuttings were potted on June 6, 1991 in a root medium of peat, perlite and soil (40:40:20 by volume) amended with N, K, Ca and micro-nutrients, plus six phosphorus (0-40-0) rates of .89, 1.78, 3.55, 7.11, 10.67, and 14.22 kg/meter3. Foliar samples were analyzed for NH4, P, and K every two weeks after the start of short days. Root media samples were also collected and analyzed pH, SS and NO3, P, K and NH4. Bract diameter, bract edge burn, days to anthesis, and plant height were recorded at anthesis.

Media P levels increased as the phosphorus rate increased, but a significant treatment*harvest interaction for media P was observed. There was decreased bract size and increased incidences of bract edge burn as phosphorus rate increased. Root media P levels did not affect the levels of other nutrient elements in the foliar samples. No visual symptoms of phosphorus toxicity was observed except for bract edge burn at anthesis.

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Brian Whipker and P. Allen Hammer

Mini-poinsettias are a popular form of potted plant, but there is a need to control plant height because tall growing cultivars are used. A study was conducted to determine the suitability of paclobutrazol to control height of mini-poinsettias. Cuttings of poinsettia cultivars Freedom and Red Sails were taken on 10 Sept. 1993 and rooted under mist. On 11 Oct. when short days began, plant height was measured and 4 plant growth regulator (PGR) treatments were applied as foliar sprays using a volume of 204 ml·m-2: paclobutrazol at 15, 30, 45 and 60 mg·liter-1, plus an untreated control. At anthesis, plant height (pot rim to top of plant) and bract diameter (measured in 2 directions and averaged) were measured. Data for plant height gain (PHG), the difference between plant height at anthesis and when PGRs were applied, and bract diameter were analyzed statistically.

PHG was significantly different at the cultivar × treatment interaction. For `Red Sails' all paclobutrazol treatments significantly retarded PHG, but there were no significant differences in PHG with increased rates of application. For `Freedom' only paclobuuazol rates at 30 and 45 mg·liter-1 significantly retarded PHG. Bract diameter was significantly different at paclobunazol rates 30 mg·liter-1 or greater, with diameter decreasing as the rate of PGR applied increased

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Douglas A. Hopper and P. Allen Hammer

A central composite rotatable design was used to estimate quadratic equations describing the relationship of irradiance, as measured by photosynthetic photon flux (PPF), and day (DT) and night (NT) temperatures to the growth and development of Rosa hybrida L. in controlled environments. Plants were subjected to 15 treatment combinations of the PPF, DT, and NT according to the coding of the design matrix. Day and night length were each 12 hours. Environmental factor ranges were chosen to include conditions representative of winter and spring commercial greenhouse production environments in the Midwestern United States. After an initial hard pinch, 11 plant growth characteristics were measured every 10 days and at flowering. Four plant characteristics were recorded to describe flower bud development. Response surface equations were displayed as three-dimensional plots, with DT and NT as the base axes and the plant character on the z-axis while PPF was held constant. Response surfaces illustrated the plant response to interactions of DT and NT, while comparisons between plots at different PPF showed the overall effect of PPF. Canonical analysis of all regression models revealed the stationary point and general shape of the response surface. All stationary points of the significant models were located outside the original design space, and all but one surface was a saddle shape. Both the plots and analysis showed greater stem diameter, as well as higher fresh and dry weights of stems, leaves, and flower buds to occur at flowering under combinations of low DT (≤ 17C) and low NT (≤ 14C). However, low DT and NT delayed both visible bud formation and development to flowering. Increased PPF increased overall flower stem quality by increasing stem diameter and the fresh and dry weights of all plant parts at flowering, as well as decreased time until visible bud formation and flowering. These results summarize measured development at flowering when the environment was kept constant throughout the entire plant growth cycle.

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Brian E. Whipker and P. Allen Hammer

Field studies were conducted on the potential of annual statice as an outdoor cut-flower crop for the Midwestern United States. Data was collected on seven cultivars in 1989 and 42 in 1990. In 1989, total fresh stem weight, stem count, and average stem weight differed significantly among cultivars. Yellow cultivars had more stems harvested than the rose, apricot, and blue cultivars, but stems of the yellow cultivars weighed less. The number of stems harvested over time tended to be concentrated in the first 8 weeks after flowering begins. In 1990, the average stem fresh weight was significantly different among the apricot, blue, and rose cultivars, but the number of stems harvested was significantly different only between the blue and rose cultivars.

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Pauline H. Andrews and P. Allen Hammer

Three cultivars each of zonal geranium (Pelargonium ×hortorum `Candy Lavender', `Fireball', and `Patriot Red') and ivy geraniums (Pelargonium pelatum `Global Deep Lilac', `Global Salmon Rose', and `Global Soft Pink') were grown in root media with pHs varying from 4.3 to 7.8. In Expt. 1, a mixture of sphagnum peat, fine perlite, and fine pine bark was modified with limestone and hydrated lime at the following rates: 0, 1.2, 3.0, 4.7, and 11.9 kg·m–3 limestone; 11.9 limestone plus 5.9 hydrated lime; 11.9 limestone plus 8.3 hydrated lime; and 11.9 kg·m–3 limestone plus 10.7 kg·m–3 hydrated lime to give the various root medium pH treatments. Plants were grown for 11 weeks in glass greenhouses. In Expt. 2, plants were grown in two commercial soilless mixes with one being modified with the addition of 0 kg·m–3 limestone, 6.0 kg·m–3 limestone plus 0.6 kg·m–3 hydrated lime, and 6.0 kg·m–3 limestone plus 2.4 kg·m–3 hydrated lime. In both experiments, greatest dry weight was recorded in zonal and ivy geraniums plants grown at root medium pHs above 6.4. This study showed a root medium pH of 6.4 to 6.5 should be recommended for the greenhouse production of both zonal and ivy geraniums.

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Brian E. Whipker and P. Allen Hammer

Chemical plant growth retardant (PGR) treatments (mg·liter–1) were applied as foliar sprays to three zonal geranium cultivars: chlormequat at 1500, applied two, three, and four times, a combination of chlormequat at 750 and daminozide at 1250, applied one and two times, and paclobutrazol applied once at 5, 10, 20, and 30; twice at 5, 10, and 15; and three times at 5, plus an untreated control. Two paclobutrazol drench treatments at 0.1 and 0.25 mg a.i. per pot were also applied. The results of the PGR applications were significant at the cultivar × treatment interaction for leaf canopy height and plant diameter. Paclobutrazol rates of 10 to 15 mg·liter–1 resulted in acceptable height control for `Medallion Dark Red' and `Aurora'. `Pink Satisfaction' is a less vigorous cultivar and lower paclobutrazol rates of 5 to 10 mg·liter–1 were more suitable. When the total concentration of the single and multiple applications were compared, no additional height control was realized with the multiple applications of paclobutrazol.

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Brian E. Whipker and P. Allen Hammer

`Supjibi' poinsettias (Euphorbia pulcherrima Willd.) were grown hydroponically for 15 weeks in nutrient solutions with 100-15-100, 200-30-200, or 300-46-300 (in mg·L-1 of N-P-K) to determine nutrient uptake patterns and accumulation rates. Results indicate that increasing fertilization rates from 100 to 300 mg·L-1 of N and K did not significantly influence the plant dry mass or the nutrient concentration of P, K, Ca, Mg, Na, B, Cu, Fe, Mn, Mo, and Zn in poinsettias. NH4-N concentration in the leaves, stems, and roots were lowest with the 100-mg·L-1 N fertilization rate and increased as the N application rate increased to 200 and 300 mg·L-1. Leaf P concentration levels from 1 week after potting through anthesis were above 1.3%, which exceeds the recommended level of 0.9%. When the plant tissue dry mass for each fertilizer rate was transformed by the natural log and multiplied by the mean tissue nutrient concentration of each fertilizer rate, there were no significant differences among the three fertilization rates when the total plant nutrient content was modeled for N, P, or K. Increasing the fertilizer application rate above 100 mg·L-1 N and K and 15 mg·L-1 P decreased total plant content of Ca, Mg, Mn, and Zn and increased the total plant Fe content. The results of the weekly nutrient uptake based on the total plant nutrient content in this study suggests that weekly fertilization rates should increase over time from potting until anthesis. Rates (in mg) that increase from 23 to 57 for N (with 33% of the total N supplied in the NH4-N form), 9 to 18.5 for P, 19 to 57 for K, 6 to 15 for Ca, and 3 to 8 for Mg can be applied without leaching to poinsettias and produce adequate growth in the northern United States.

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Brian E. Whipker and P. Allen Hammer

Plant growth retardant (PGR) substrate drench treatments (mg a.i./1.5-L pot) of ancymidol at doses of 0.5 to 8, paclobutrazol from 1 to 16, and uniconazole from 0.125 to 2 were applied to tuberous-rooted dahlias (Dahlia variabilis Willd.) to compare their effectiveness for controlling height. When the first inflorescence opened, the number of days from potting until flowering, leaf canopy height, inflorescence height above the foliage, and plant diameter were recorded. Total height control achieved using PGRs was primarily due to reduced inflorescence height, rather than leaf canopy height. Paclobutrazol, ancymidol, and uniconazole at all doses reduced total plant height of the less-vigorous `Red Pigmy' by >21% compared to the untreated control, with a height of 43.5 cm for the untreated control plants. Marketable potted plants were produced with doses of 2 to 4 mg of paclobutrazol, 0.25 to 0.5 mg of uniconazole, or 0.5 mg of ancymidol. All paclobutrazol, ancymidol, and uniconazole doses reduced total plant height of the more-vigorous `Golden Emblem' by >11% compared to the untreated control, with a height of 82.1 cm for the untreated control. Marketable potted plants were produced with 4 to 8 mg of paclobutrazol, 0.5 to 1 mg of uniconazole, or 2 mg of ancymidol.

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Douglas C Needham and P. Allen Hammer

Salpiglossis sinuata R. et P., a floriferous member of the Solanaceae, was studied for potential as a flowering potted plant when modified by growth retardants. Seedlings of an inbred line P-5 were covered with black cloth for an 8-hour photoperiod to permit vegetative growth to ≈16 -cm-diameter rosettes. Plants were then exposed to an 18-hour photoperiod for the duration of study. Flowering occurred 40 days after the plants were transferred to long days. Neither spray applications of uniconazole at 10, 20, 40, or 100 ppm, nor chlormequat chloride at 750, 1500, or 3000 ppm significantly retarded plant height. Applications of daminozide, ranging in concentration from 1000 to 5000 ppm, alone and in combination with chlormequat chloride, were effective at retarding plant height; however, concomitant restriction of corolla diameter was frequently observed. Chemical names used: 2-chloro- N,N,N -trimethylethanaminium chloride (chlormequat chloride); butanedioic acid mono(2,2-dimethylhydrazide) (daminozide); and (E) -1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl) -1-penten-3-01 (uniconazole).

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Pauline H. Andrews and P. Allen Hammer

Limestone requirement tests are routine in agronomic laboratories; however, no tests exist for soilless root medium although there is still a need to predict the limestone additions. This research was to develop a rapid, accurate test to determine the limestone requirement of soilless root media for a specific pH. Thirty-four media formulations were amended with increasing rates of limestone. Media were incubated in the greenhouse. Pots were irrigated to container capacity every 2 days with RO-water; pH was recorded after 5 weeks; and limestone requirement for pH 5.5 was determined for each media. A modified SMP buffer procedure for mineral soils was used. A 40-mL aliquot of the SMP buffer was added to 6 g of media, equilibrated for 48 hours and pH determined. Media-buffer pH was plotted against the incubation limestone requirement for pH 5.5. A separate regression was required for media containing coir since the modified SMP buffer test overestimated the limestone requirement of coir media. The correlation for non-coir media was –0.97 (Y = -1.19x + 7.52) and -0.94 (Y = –1.12x + 6.14) for coir media. The procedure was verified using 15 media. Media-buffer pH was determined and the limestone requirement was calculated using the corresponding regression equation. Two sets of media treatments were potted and incubated in the greenhouse. Rooted cuttings of geranium `Candy Lavender' were transplanted into one set of pots. Pots were irrigated every 2 days with RO-water and geraniums were irrigated with nonacidified fertilizer water. Media pH was determined at week 5. Media was nonsignificant for pots or geraniums (P ≤ 0.01). The mean pH of non-coir media was pH 5.66 and 5.67 for pots and geraniums and pH 5.39 and 5.39, respectively, for coir media.