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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

In 2002 the USDA reported potted geraniums accounted for $150 million in wholesale value, more than any other bedding or garden plant surveyed. Despite the importance of the geranium in floriculture production, little published research data is available pertaining to the media pH requirements of zonal and ivy geraniums. Current recommendations suggest zonal geraniums be grown at pH 5.7-6.6 and ivy geraniums at pH 5.0-6.2. The wide range in root medium pH recommendations for both zonal and ivy geraniums and the lack of research data prompted this research. Also, the basis for recommending a lower medium pH for ivy geraniums could not be found in published literature. The research objectives were to investigate the effect of medium pH on plant growth and to determine more precise recommendations for both species. The growth of 3 cultivars each of zonal and ivy geraniums growing in 8 medium pH treatments were evaluated. Limestone and hydrated lime were incorporated at increasing rates into a 1:1:1 peat, perlite and bark mix to achieve a medium pH ranging from pH 4.0-7.5. Plants were harvested at weeks 3, 6, and 11 and plant dry weight and media pH were determined. Leaf luminance, chroma and hue were evaluated at week 10. Plant dry weight was greatest at pH 6.55 or higher for both zonal and ivy geraniums at week 11. Leaves of plants grown at pH 6.55 or higher had significantly lower luminance and chroma and greater hue in all cultivars, corresponding to leaves that were darker, less vivid, and deeper green in color. This study shows a root medium pH greater than pH 6.5 results in greatest plant dry weight accumulation and quality of leaf color for both zonal and ivy geraniums. This study also shows ivy geraniums can be grown at the same media pH as zonal geraniums.

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.

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.

Eight poinsettia (Euphorbia pulcherrima Wind.) cultivars (`Angelika White', `Celebrate 2', `Dark Red Hegg', `Jingle Bells 3', `Pink Peppermint', `Red Sails', `Supjibi', and `V-14 Glory') were grown in root medium amended with six triple superphosphate rates of 0.39,0.78, 1.55,3.11,4.66, and 6.21 kg P/m³. Root medium and foliar samples of `Supjibi' and `Celebrate 2' were sampled every 4 weeks, starting with the beginning of short days. At flowering, all eight cultivars were measured for diameter of the two largest bracts, number of bracts with burn, and plant height. Foliar P levels increased over the growing season for `Supjibi' with a reading of 0.9% at anthesis, but for `Celebrate 2', levels peaked 4 weeks before anthesis (0.8%). At triple superphosphate rates > 3.11 kgP/m³, plant height decreased, and there was a significant cultivar × treatment interaction for descreased bract diameter. The eight cultivars exhibited varying degrees of susceptibilities to bract-edge burn as the amount of P applied to the root medium increased, with `Dark Red Hegg', `V-14 Glory', and `Red Sails' having the highest burn incidence.

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.

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.