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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.

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

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).

Plant growth retardant (PGR) media drench treatments (in mg a.i./pot) of ancymidol at 0.5, 1.0, 2.0, 4.0, or 8.0; paclobutrazol at 1.0, 2.0, 4.0, 8.0, or 16.0; uniconazole at 0.5, 1.0, 2.0, 4.0, or 8.0 were applied to tuberous-rooted dahlias to compare their effectiveness as a chemical height control. All paclobutrazol, ancymidol, and uniconazole rates applied significantly reduced `Red Pigmy' plant height by 21% or greater compared to the nontreated control. Excessively short plants resulted from uniconazole and ancymidol drench rates ≥1.0 mg. `Red Pigmy', a less vigorous cultivar, were acceptable as potted-plants with paclobutrazol rates of 2.0 to 4.0 mg, 0.25 to 0.5 mg of uniconazole, or 0.5 mg of ancymidol. All paclobutrazol, ancymidol, and uniconazole rates significantly reduced `Golden Emblem' plant height by ≥11% when compared to the nontreated plants. Excessively short plants resulted from paclobutrazol drench rates of 16.0 mg, uniconazole rates of 2.0 mg and for ancymidol drenches ≥4.0 mg. `Golden Emblem', the more vigorous cultivar, were acceptable as potted-plants with paclobutrazol rates of 4.0 to 8.0 mg, 0.5 to 1.0 mg of uniconazole, or 2.0 mg of ancymidol.

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.

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.

`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.

Excessive alkalinity in greenhouse irrigation water can increase substrate solution pH, resulting in reduced micronutrient availability for plants. A spreadsheet was designed to offer a quick and practical method for calculating: 1) amount of nitric, phosphoric, and sulfuric acid required to achieve an endpoint alkalinity or pH in irrigation water; 2) the amount of nutrients added by the acid addition; and 3) acid costs. It calculates both pH and alkalinity of irrigation water after acidification, regardless of the endpoint selected. The spreadsheet accounts for the pH-dependent reaction that determines the relative percentage of each of the carbonate species—carbonates (CO ^2– ₃), bicarbonates (HCO^– ₃), and carbonic acid (H₂CO³)—present in the solution. In addition, the acidification calculations account for the dissociation characteristics of the acid selected to neutralize the alkalinity. The spreadsheet was validated with six water sources from Indiana and North Carolina. Alkalinity neutralization was achieved within an acceptable range (greatest deviation from predicted pH was 0.16 units; greatest deviation from predicted residual alkalinity was 0.21 meq·liter^–1) for both target endpoint pHs and endpoint alkalinity concentrations. The mathematical model used in the spreadsheet development provides a chemical basis for acidification and provides results useful for making grower recommendations for acid additions to irrigation water for alkalinity neutralization.

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.