Ingram McCall

GERANIUM LEAF TISSUE NUTRIENT SUFFICIENCY RANGES BY CHRONOLOGICAL AGE

Two cultivars of geranium (Pelargonium × hortorum) were grown under five different fertilizer regimes, 50, 100, 200, 300, or 400 mg·L−1 nitrogen (N). The two cultivars were chosen to represent a dark-colored leaf cultivar, ‘Tango Dark Red’ and a light-colored leaf cultivar, ‘Rocky Mountain Dark Red’. Tissue samples were collected and analyzed for the content of 11 elemental nutrients every two weeks for a period of 12 weeks. The dark-colored leaf cultivar contained higher nutrient concentrations, with the exception of magnesium, sulfur, iron, and copper, than the light-colored leaf cultivar. Compared to concentrations previously published for geraniums, concentration ranges observed in this study were narrower. In addition, this study accounted for differences in concentrations over the entire crop cycle and reflects levels associated with current fertilization practices.

Growth Response of Herbaceous Ornamentals to Phosphorus Fertilization

A series of experiments investigated the effects of increasing phosphate– phosphorus (P) concentrations on the growth and development of four horticultural species. In experiment 1, petunia [Petunia atkinsiana (Sweet) D. Don ex W.H. Baxter] plants were grown using eight P concentrations, and we found that the upper bound for plant growth was at 8.72–9.08mg·L P, whereas concentrations £2.5 mg·L P caused P deficiency symptoms. Experiment 2 investigated P growth response in two cultivars each of New Guinea impatiens (Impatiens hawkeri W. Bull) and vinca [Catharanthus roseus (L.) G. Don]. Growth for these plants was maximized with 6.43–12.42 mg·L P. In experiment 3, ornamental peppers (Capsicum annuum L. ‘Tango Red’) were given an initial concentration of P for 6 weeks and then switched to 0mg·L P to observe whether plants could be supplied with sufficient levels of P, and finished without P to keep them compact. Plants switched to restricted P began developing P deficiency symptoms within 3 weeks; however, restricting P successfully limited plant growth. These experiments indicated that current P fertilization regimens exceed the P requirements of these bedding plants, and depending on species, concentrations of 5–15 mg·L P maximize growth. Producers of floriculture crops strive to cultivate compact and healthy plants that are considered high quality and attractive for consumers. The fertilization regimen has a significant role in the ultimate appearance and robustness of a crop. Many commercial fertilizers mixed at recommended concentrations for greenhouse production supply greater phosphorus (P) concentrations than required by plants, as is the case with 20 nitrogen (N)– 8.7P–16.6 potassium (K). This fertilizermixed at a concentration of 200 mg·L N would provide 87 mg·L P. One recommendation for greenhouse crops by McMahon (2011) suggests using concentrations of only 5–10 mg·L P. Other studies have indicated that P concentrations of just 0.093–1.5 mg·L can keep floriculture crops healthy yet compact (Borch et al., 1998; Hansen and Nielsen, 2000, 2001). This disparity among P recommendations and P concentrations supplied in common fertilizers brings into question what level of P is required to produce healthy floriculture crops. Recent research investigated the minimum P concentrations required by herbaceous ornamentals (Borch et al., 1998; Hansen and Nielsen, 2000, 2001; Nelson et al., 2012). These studies were focused on the potential of using low P fertilization to control plant growth. Although the nitrate (NO3 ) form of N has often been used to keep plants compact, it is the low P levels in high NO3 –N fertilizers that are responsible for compactness (Nelson et al., 2012). Most NO3 – based fertilizers recommended for compact plant growth are also low in P. Erroneously, it was thought that fertilizer formulations high in ammoniacal nitrogen (NH4 ) result in greater plant growth. Experiments conducted by Nelson et al. (2002) used constant ratios of N source, but varied P concentrations, and found that plant size increased with increasing P concentrations. Previously, it was thought that higher P concentrations would only increase growth until plant P concentration reached 0.25% of total dry matter (Nelson et al., 2002). Potential issues with very low P fertilization result from the fact that the soilless substrates used in floriculture production have limited P holding capacity (Marconi and Nelson, 1984). Without adequate P, crops have the potential to deplete the initial P concentration in the substrate and may begin reallocating P from older plant tissues, leading to the development of deficiency symptoms on the lower leaves (Mengel et al., 2001). Deficiency symptoms associated with P are commonly observed when dry plant tissue comprises <0.2% or 2000 mg·kg P (Mills and Jones, 1996). Typical symptoms are often described as a reddening or purpling of the lower foliage, an overall darker green coloration, stunted growth, delayed flowering, and greater root lengths (Epstein and Bloom, 2005; Marschner, 1995; Mengel et al., 2001). For leaf tissue concentrations, a range of 0.2% to 0.5% of total plant dry weight is considered sufficient P for most plants (Mills and Jones, 1996). This study aimed to determine the P concentration required by several floriculture species to optimize growth. Determining optimal P concentrations will provide improved grower recommendations and limit commercial fertilizer waste. Materials and Methods Experiment 1. Two cultivars of petunia [Petunia atkinsiana (Sweet) D. Don ex W.H. Baxter ‘Surprise Sky Blue’ and ‘Potunia Neon’] cuttings (D€ummen Orange, Columbus, OH) were planted on 28 Sept. 2015 in 128 cell plug trays with cell dimensions of 2.7 · 2.7 · 3.8 cm (length · width · depth) and rooted under mist without fertilization. Plants were propagated and grown in a glassglazed greenhouse at North Carolina State University, Raleigh, NC (35 N latitude) under natural photoperiod. Greenhouse day/night temperature set points were 23.9/18.3 C, and the average daily temperature (ADT) was 19.7 C. The substrate used for all aspects of the experiment was an 80:20 (v:v) mix of Canadian sphagnum peatmoss (Conrad Fafard, Agawam, MA) and horticultural coarse perlite (Perlite Vermiculite Packaging Industries, Inc., North Bloomfield, OH), amended with dolomitic limestone at 8.875 kg·m (Rockydale Agricultural, Roanoke, VA) and wetting agent (AquaGro 2000 G; Aquatrols, Cherry Hill, NJ) at 600.3 g·m. This custom substrate was used to ensure that there was no initial P concentration. Twenty-eight-day old rooted cuttings were transplanted into 12.7 cm diameter (855 mL) pots (Dillen, Middlefield, OH). Concentrations of 0, 1.25, 2.5, 5, 10, 20, 40, and 80 mg·L P were used to determine the upper and lower bounds of growth response to P. The experiment was completely randomized with eight single-plant replications of eight treatments. Fertilization began at transplant, and fertilizers were custom blends of the following individual technical grade salts: calcium nitrate tetrahydrate [Ca(NO3)2·4H2O], potassium nitrate (KNO3), monopotassium phosphate (KH2PO4), potassium sulfate (K2SO4), magnesium sulfate heptahydrate (MgSO4·7H2O), magnesium nitrate [Mg(NO3)2], iron chelate (FeDTPA), manganese chloride tetrahydrate (MnCl2·4H2O), zinc chloride heptahydrate (ZnCl2·7H2O), copper chloride dihydrate (CuCl2·2H2O), boric acid (H3BO3), and sodium molybdate dihydrate (Na2MoO4·2H2O). Phosphorus (referring to phosphate-phosphorus) concentrations were varied among treatments whereas other essential nutrients were adjusted to remain as constant as possible. NO3 – N and K were held at 150 mg·L, with all other essential microelements remaining constant (Henry, 2017). Received for publication 21 June 2017. Accepted for publication 21 Aug. 2017. We are grateful for the funding support provided by the Fred C. Gloeckner Foundation, the USDA Floriculture and Nursery Research Initiative, American Floral Endowment Altman Family Scholarship, and The Garden Club of America. We would also like to express our gratitude to D€ummen Orange for providing cuttings and for peat moss provided by Sun Gro Horticulture. Corresponding author. E-mail: josh.brady.henry@

Phosphorus Restriction as an Alternative to Chemical Plant Growth Retardants in Angelonia and New Guinea Impatiens

Chemical plant growth retardants (PGRs) are commonly used to produce compact bedding plants. Few PGRs are labeled for sensitive species because of the concern of excessive restriction of stem elongation or phytotoxicity. Growers are therefore presented with a dilemma: produce untreated plants that may be too tall or risk applying a PGR that can potentially lead to irreversible aesthetic damage to the plant. Nutrient restriction, specifically of phosphorus (P), may be used to control plant height. This study was conducted to determine if restricting P fertilization yielded comparable growth control to plants produced with PGRs. Two cultivars each of new guinea impatiens (Impatiens hawkeri) and angelonia (Angelonia angustifolia) were grown using five fertilizers that varied by P concentration (0, 2.5, 5, 10, and 20 ppm). Half of the plants from each P fertilizer concentration were treated with paclobutrazol at 4 and 5 weeks after transplant for angelonia and new guinea impatiens, respectively. On termination of the experiment, data were collected for height, diameter, and dry weight, which were used to determine a growth index (GI). Angelonia GI values weremaximized with 7–9 ppm P, whereas new guinea impatiens GI was maximized with 8–11 ppm P. Concentrations of 3–5 ppm P provided similar height control to plants grown with nonlimiting P and a paclobutrazol application. Concentrations of £2.5 ppm P resulted in low-quality plants with visual symptoms of P deficiency. These results indicate that a narrow range of P concentrations may be used to control stem elongation and keep plants compact.

Nutrient disorders of Dianthus ‘Bouquet Purple’

ABSTRACT ‘Bouquet Purple’ pinks (Dianthus sp.) were grown in silica-sand culture to induce and photograph symptoms of nutritional disorders. Plants received a complete modified Hoaglands all-nitrate (NO3) solution. Nutrient-deficient treatments were induced with a complete nutrient formula minus one of the nutrients, and a boron (B)-toxicity treatment was induced by increasing B 10-fold in the complete nutrient formula. Plants were monitored daily to document sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and corresponding tissue concentrations were determined. All treatments exhibited deficiency symptomology. Disorders for nitrogen (N), iron (Fe), calcium (Ca), and sulfur (S) were the first to manifest in pinks. Unique symptomology was observed for plants grown under potassium- (K), B-, copper- (Cu), and molybdenum- (Mo) deficient conditions, which supported the need for a species-specific approach when characterizing nutrient disorders of floriculture crops.