Current research efforts of the Owen Lab include:

1. Plant growth regulators for annual bedding plants, herbaceous perennials, and woody ornamental nursery stock.
2. Carbon and water foot-printing of greenhouse crops.
3. Plant nutrition of floriculture crops and vegetable transplants
4. Hydroponic high-wire greenhouse vegetables and leafy greens crop production.

Rooting Response of Herbaceous Perennial Cuttings to Foliar Applications of a Novel Indole-3-butyric Acid Liquid Product

A research trial was conducted to evaluate a novel indole-3-butyric acid (IBA) liquid-based product for rooting of herbaceous perennial cuttings. Foliar spray applications of deionized water (0 mg∙L^‒1) or 200, 400, 800, or 1200 mg∙L^‒1 IBA were applied to unrooted cuttings of ‘Lemoncello Golden’ coreopsis (Coreopsis auriculate), ‘Sweet Daisy Christine’ shasta daisy (Leucanthemum maximum), Flame PinkP ®P (‘Bartwelve’) garden phlox (Phlox paniculata), and ‘Salute Pink’ meadow sage (Salvia nemerosa) 1 day after placement into propagation trays. For all genera, stem caliper, shoot length, and shoot dry weight were unaffected by increasing IBA concentrations at 21 days while rooting varied. Shasta daisy root dry weight increased by 123% from 0 to 800 mg∙L^‒1 IBA and then decreased. For coreopsis, garden phlox, and meadow sage, root dry weight was unaffected by IBA concentration. Hastened rooting and increased root dry weight is important to propagators who desire high-quality rooted liners therefore further investigation is warranted. Overall, 200–800 mg∙L^‒1 IBA foliar spray applications resulted in similar rooting among the perennials trialed.

Owen, W.G. 2021. Rooting response of herbaceous perennial cuttings to foliar applications of a novel indole-3-butyric acid liquid product. Intl. J. Innovative Sci. Eng. Technol. 8(11):417–420. http://ijiset.com/vol8/v8s11/IJISET_V8_I11_37.pdf

Establishment of Leaf Tissue Nutrient Sufficiency Ranges of Two Perovskia Selections by Chronological Age

The objective of this study was to determine optimum fertilizer concentrations, identify leaf tissue nutrient sufficiency ranges by chronological age, and establish leaf tissue nutrient standards of containerized Russian sage (Perovskia sp.). Common Russian sage (P. atriplicifolia Benth.) and ‘Crazy Blue’ Russian sage were greenhouse-grown in a soilless substrate under one of six constant liquid fertilizer concentrations [50, 75, 100, 200, 300, or 400 mg·L⁻¹ nitrogen (N)] with a constant level of a water-soluble micronutrient blend. Fertilizer concentrations sufficient for optimal plant growth and development were determined by analyzing plant height, diameter, growth index, primary shoot caliper, axillary shoot number, and total dry mass; they were found to be 100 to 200 mg·L⁻¹ N after a 6-week crop cycle. Recently, mature leaf tissue samples were collected from plants fertilized with 100 to 200 mg·L⁻¹ N and analyzed for elemental contents of 11 nutrients at 2, 4, and 6 weeks after transplant (WAT). An overall trend of increasing foliar nutrient concentrations over time was observed for all elemental nutrients. For instance, at 2 WAT, the total N concentrations of common Russian sage and ‘Crazy Blue’ Russian sage ranged between 3.68% and 5.10% and between 3.92% and 5.12%, respectively, and increased to ranges of 5.94% to 5.98% and 5.20% to 5.86% at 6 WAT, respectively. Before this study, no leaf tissue concentration standards have been reported; therefore, this study established leaf tissue concentration sufficiency ranges for the trialed Perovskia selections.

Owen, W.G. 2020. Establishment of leaf tissue nutrient sufficiency ranges of two Perovskia selections by chronological age. HortScience 55:1303-1307. https://doi.org/10.21273/HORTSCI15124-20

A National Survey to Characterize Industrial Hemp (Cannabis sativa L.) Production Challenges Under Protected Cultivation

A nationwide internet survey (n = 134) was conducted to establish the current status of industrial hemp (IH; Cannabis sativa L.) cultivation and characterize protected culture production challenges in the United States. Of the total participants, 65.7% (n = 88) of the subjects reported current production of IH. These participants were asked to identify all production systems and included growing IH indoors (e.g., shipping containers, buildings or warehouses; 15.9%), in greenhouses (29.5%), in hoop houses or high tunnels (15.9%), or in outdoor fields in-ground (62.5%). Of the respondents who identified as growing under protected culture (e.g., indoors, greenhouses, and hoop houses/ high tunnels), most grew IH in soilless substrate and provided mineral nutrition, electrical lighting, and monitored plant health. Participants reported the most important production challenges of IH cultivation were at or post-harvest and included drying, harvesting and handling, processing, and CBD oil enhancement; several key production challenges including insect pest management strategies and environmental growing conditions; and variety/cultivar evaluations. Furthermore, respondents reported that the most important economic topic or challenge was return on investment. Results characterize current cultivation practices of IH, identify knowledge gaps, and prioritize education and research areas for the successful production and marketing of IH.

Owen, W.G. and B.K. Behe. 2020. A national survey to identify industrial hemp (Cannabis sativa L.) production challenges under protected cultivation. J. Agr. Hemp. 2:1–24. https://digitalcommons.murraystate.edu/jahr/vol1/iss2/4/https://digitalcommons.murraystate.edu/jahr/vol1/iss2/4/

Liming Requirements of Greenhouse Peat-based Substrates Amended with Pine Wood Chips as a Perlite Alternative

Processed loblolly pine (Pinus taeda) wood has been investigated as a component in greenhouse and nursery substrates for many years. Specifically, pine wood chips (PWCs) have been uniquely engineered/processed into a nonfibrous blockular particle size suitable for use as a substrate aggregate. The objective of this research was to compare the dolomitic limestone requirements of plants grown in peat-based substrates amended with perlite or PWC. In a growth trial with ‘Mildred Yellow’ chrysanthemum (Chrysanthemum ×morifolium), peat-based substrates were amended to contain 0%, 10%, 20%, 30%, 40%, or 50% (by volume) perlite or PWC for a total of 11 substrates. Substrates were amended with dolomitic limestone at rates of 0, 3, 6, 9, or 12 lb/yard³, for a total of 55 substrate treatments. Results indicate that pH of substrates amended with ≥30% perlite or PWC need to be adjusted to similar rates of 9 to 12 lb/yard³ dolomitic limestone to produce similar-quality chrysanthemum plants. In a repeated study, ‘Moonsong Deep Orange’ african marigold (Tagetes erecta) plants were grown in the same substrates previously formulated (with the exclusion of the 50% ratio) and amended with dolomitic limestone at rates of 0, 3, 6, 9, 12, or 15 lb/yard³, for a total of 54 substrate treatments. Results indicate a similar dolomitic limestone rate of 15 lb/yard³ is required to adjust substrate pH of 100% peatmoss and peat-based substrates amended with 10% to 40% perlite or PWC aggregates to the recommended pH range for african marigold and to produce visually similar plants. The specific particle shape and surface characteristics of the engineered PWC may not be similar to other wood products (fiber) currently commercialized in the greenhouse industry, therefore the lime requirements and resulting substrate pH may not be similar for those materials.

Owen, W.G., B.E. Jackson, W.C. Fonteno, and B.E. Whipker. 2020. Liming requirements of greenhouse peat-based substrates amended with pine wood chips as an alternative to perlite. HortTechnology 30:219–230. https://doi.org/10.21273/HORTTECH04506-19

Response of Calceolaria ×herbeohybrida Cultivars to Substrate pH and Corresponding Leaf Tissue Nutrient Concentration Effects

Calceolaria (Calceolaria ×herbeohybrida) is a flowering potted greenhouse crop that often develops upper-leaf chlorosis, interveinal chlorosis, and marginal and leaf-tip necrosis (death) caused by cultural practices. The objectives of this research were to 1) determine the optimal incorporation rate of dolomitic and/or hydrated lime to increase substrate pH; 2) determine the influence of the liming material on substrate pH, plant growth, and leaf tissue nutrient concentrations; and 3) determine the optimal substrate pH to grow and maintain during calceolaria production. Sphagnum peatmoss was amended with 20% (by volume) perlite and incorporated with pulverized dolomitic carbonate limestone (DL) and/or hydrated limestone (HL) at the following concentrations: 48.1 kg·m⁻³ or 144.2 kg·m⁻³ DL, 17.6 kg·m⁻³ DL + 5.3 kg·m⁻³ HL, or 17.6 kg·m⁻³ DL + 10.6 kg·m⁻³ HL to achieve a target substrate pH of 4.5, 5.5, 6.5, and 7.5, respectively. Calceolaria ‘Orange’, ‘Orange Red Eye’, ‘Yellow’, and ‘Yellow Red Eye’ were grown in each of the prepared substrates. For all cultivars, substrate solution pH increased as limestone incorporation concentration and weeks after transplant (WAT) increased, although to different magnitudes. For example, as limestone incorporation increased from 48.1 kg·m⁻³ DL to 17.6 kg·m⁻³ DL + 10.6 kg·m⁻³ HL, substrate solution pH for ‘Orange’ calceolaria increased from 4.1 to 6.9 to 4.8 to 7.2 at 2 and 6 WAT, respectively. Substrate solution electrical conductivity (EC) and growth indices were not influenced by limestone incorporation, but total plant dry mass increased. Few macronutrients and most micronutrients were influenced by limestone incorporation. Leaf tissue iron concentrations for ‘Orange’, ‘Orange Red Eye’, ‘Yellow’, and ‘Yellow Red Eye’ calceolaria decreased by 146%, 91%, 71%, and 84%, respectively, when plants were grown in substrates incorporated with increasing limestone concentrations from 144.2 kg·m⁻³ DL to 17.6 kg·m⁻³ DL + 10.6 kg·m⁻³ HL (pH 6.5–6.9). Therefore, incorporating 144.2 kg·m⁻³ DL into peat-based substrates and maintaining a pH <6.5 will avoid high pH–induced Fe deficiency and prevent upper-leaf and interveinal chlorosis.

Owen, W.G. 2019. Response of Calceolaria ×herbeohybrida cultivars to substrate pH and susceptibility to iron deficiency. HortScience 54:2163–2168. https://doi.org/10.21273/HORTSCI14449-19

Leaf Tissue Nutrient Sufficiency Ranges of Four Heuchera Cultivars by Chronological Age

Coral bells (Heuchera sp.) are popular herbaceous perennials grown for their colorful foliage and venation and their aesthetic appeal in mixed containers and landscapes. Commercial coral bell production requires greenhouse or nursery growers to optimize production inputs such as managing mineral nutrition, thereby maximizing plant growth potential and foliage color. The objective of this study was to determine the optimum fertilizer concentrations, identify leaf tissue nutrient sufficiency ranges by chronological age, and to expand leaf tissue nutrient standards of coral bells grown in soilless substrates during container production. Coral bells (H. hybrida ‘Black Beauty’, ‘Cherry Cola’, ‘Marmalade’, and ‘Peppermint Spice’), varying in leaf color, were grown under one of six constant liquid fertilizer concentrations [50, 75, 100, 200, 300, or 400 mg·L⁻¹ nitrogen (N)] with a constant level of water-soluble micronutrient blend in a greenhouse. Fertilizer concentrations for optimal plant growth and development were determined by analyzing plant height, diameter, growth index, and total dry mass, and were found to be 50 to 75 mg·L⁻¹ N after a nine-week crop cycle. Recently mature leaf tissue samples were collected and analyzed for elemental content of 11 nutrients at 3, 6, and 9 weeks after transplant (WAT) from plants fertilized with 50 to 75 mg·L⁻¹ N. The black- (‘Black Beauty’) and red- (‘Cherry Cola’) colored-leaved cultivars contained higher total N, phosphorus (P), potassium (K), calcium (Ca), sulfur (S), zinc (Zn), and boron (B) than the orange- (‘Marmalade’) and green- (‘Peppermint Spice’) colored-leaved cultivars. For instance, in mature growth, total N concentration for ‘Black Beauty’ and ‘Cherry Cola’ ranged between 3.45 to 3.63% and 3.92% to 4.18% N, respectively, whereas for ‘Marmalade’ and ‘Peppermint Spice’, ranges were between 2.98% to 3.25% and 2.78% to 3.23% N, respectively. Optimal leaf tissue concentration sufficiency ranges determined in this scientifically based study were narrower and often times higher than previously reported survey values for coral bells.

Owen, W.G. 2019. Leaf tissue nutrient sufficiency ranges of four Heuchera cultivars by chronological age. HortScience 54:1751–1756. https://doi.org/10.21273/HORTSCI14222-19

Comparison of Sole-source and Supplemental Lighting on Callus Formation and Initial Rhizogenesis of Gaura and Salvia Cuttings

Variability in outdoor daily temperatures and photosynthetic daily light integrals (DLIs) from early spring to late fall limits the ability of propagators to accurately control propagation environments to consistently callus, root, and yield compact herbaceous perennial rooted liners. We evaluated and compared the effects of sole-source lighting (SSL) delivered from red (R) and blue (B) light-emitting diodes (LEDs) to supplemental lighting (SL) provided by high-pressure sodium (HPS) lamps on herbaceous perennial cutting morphology, physiology, and growth during callusing and initial rhizogenesis. Cuttings of perennial sage (Salvia nemorosa L. ‘Lyrical Blues’) and wand flower (Gaura lindheimeri Engelm. and A. Gray ‘Siskiyou Pink’) were propagated in a walk-in growth chamber under multilayer SSL provided by LEDs with [R (660 nm)]:[B (460 nm)] light ratios (%) of 100:0 (R₁₀₀:B₀), 75:25 (R₇₅:B₂₅), 50:50 (R₅₀:B₅₀), or 0:100 (R₀:B₁₀₀) delivering 60 µmol·m⁻²·s^–1 for 16 hours (total DLI of 3.4 mol·m⁻²·d⁻¹). In a glass-glazed greenhouse (GH control), cuttings were propagated under ambient solar light and day-extension SL provided by HPS lamps delivering 40 µmol·m⁻²·s^–1 to provide a 16-hour photoperiod (total DLI of 3.3 mol·m⁻²·d⁻¹). At 10 days after sticking cuttings, callus diameter and rooting percentage were similar among all light-quality treatments. For instance, callus diameter, a measure of growth, of wand flower cuttings increased from an average 1.7 mm at stick (0 day) to a range of 2.7 to 2.9 mm at 10 days after sticking, regardless of lighting treatment. Relative leaf chlorophyll content was generally greater under SSL R₇₅:B₂₅ or R₅₀:B₅₀ than all other light-quality treatments. However, stem length of perennial sage and wand flower cuttings propagated under SSL R₅₀:B₅₀ at 10 days were 21% and 30% shorter and resulted in 50% and 8% greater root biomass, respectively, compared with those under SL. The herbaceous perennial cuttings propagated in this study under SSL R₅₀:B₅₀ were of similar quality or more compact compared with those under SL, indicating that callus induction and initial rooting can occur under LEDs in a multilayer SSL propagation system.

Owen, W.G. and R.G. Lopez. 2019. Comparison of sole-source and supplemental lighting on callus formation and initial rhizogenesis of Gaura and Salvia cuttings. HortScience 54:684–691. https://doi.org/10.21273/HORTSCI13481-18

Hibiscus Leaf Tissue Nutrient Sufficiency Ranges by Chronological Age

Perennial hibiscus (Hibiscus sp.) are popular summer-flowering plants that are grown in greenhouses or nurseries, where growers must optimize production inputs such as fertility to maximize plant growth and produce high-quality flowering crops. The objective of this study was to determine the optimum fertilizer concentrations, identify leaf tissue nutrient sufficiency ranges by chronological age, and to expand leaf tissue nutrient standards of Hibiscus hybrid L. (hibiscus) grown in soilless substrates during container production. Two cultivars of hibiscus (H. hybrid L. ‘Mocha Moon’ and ‘Starry Starry Night’) were grown under one of six constant liquid fertilizer concentrations [50, 75, 100, 200, 300, or 400 mg·L⁻¹ nitrogen (N)] with a constant level of water-soluble micronutrient blend in a greenhouse. The fertilizer concentrations sufficient for optimal plant growth and development were determined by analyzing plant height, diameter, growth index (GI), primary shoot caliper (PSC), and total dry mass, and they were found to be 100–300 mg·L⁻¹ N after an 8-week crop cycle. Recently, mature leaf tissue samples were collected and analyzed for elemental content of 12 nutrients at 2, 4, 6, and 8 weeks after transplant (WAT) from plants fertilized with 100–300 mg·L⁻¹ N. An overall trend of increasing sufficient tissue concentration over time was observed for total N, phosphorus (P), calcium (Ca), sulfur (S), zinc (Zn), copper (Cu), and boron (B), whereas a decreasing trend was observed for potassium (K), iron (Fe), manganese (Mn), and aluminum (Al). For instance, at 2 WAT, total N ranged from 3.1% to 5.1% N and increased to a range of 4.2% to 4.7% N at 8 WAT. At 2 WAT, Fe and Mn ranged from 79.2 to 103.6 mg·L⁻¹ Fe and 66.3–82.8 mg·L⁻¹ Mn and decreased to ranges of 75.6–82.9 mg·L⁻¹ Fe and 18.1–99.7 mg·L⁻¹ Mn at 8 WAT, respectively. Optimal leaf tissue concentration sufficiency ranges determined in this scientifically-based study were narrower than previously reported survey values for the genera Hibiscus.

Owen, W.G. 2019. Hibiscus leaf tissue nutrient sufficiency ranges by chronological age. HortScience 54:463–469. https://doi.org/10.21273/HORTSCI13482-18

Low Substrate pH–Induced Iron/Manganese Toxicity of New Guinea Impatiens: A Diagnostic Guide

New Guinea impatiens (Impatiens hawkeri) are popular bedding plants, but the knowledge of diagnosing abiotic disorders during greenhouse production is evolving. Symptomology of nutrient deficiencies and excessive fertilization have been extensively documented. Exact symptomology of low substrate pH (<5.5) and toxic iron (Fe) and/or manganese (Mn) leaf tissue levels are not defined or photographed, thereby aiding in diagnosis. Therefore, the objective of the diagnostic guide was to photograph symptomology and document the tissue levels in New Guinea impatiens to provide a definitive guide of low substrate pH–induced Fe and/or Mn toxicity.

Owen, W.G., B.E. Whipker, J.B. Henry, P, Cockson, and H. Landis. 2018. Low substrate pH-induced iron/manganese toxicity of New Guinea impatiens: A diagnostic guide. Plant Health Prog. 19:324–328. https://doi.org/10.1094/PHP-06-18-0031-DG

Promotion of Flowering from Far-red Radiation Depends on the Photosynthetic Daily Light Integral

Under natural short days, growers can use photoperiodic lighting to promote flowering of long-day plants and inhibit flowering of short-day plants. Unlike traditional lamps used for photoperiodic lighting, low-intensity light-emitting diode (LED) lamps allow for a wide array of adjustable spectral distributions relevant to regulation of flowering, including red (R) and white (W) radiation with or without far-red (FR) radiation. Our objective was to quantify how day-extension (DE) photoperiodic lighting from two commercially available low-intensity LED lamps emitting R + W or R + W + FR radiation interacted with daily light integral (DLI) to influence stem elongation and flowering of several ornamental species. Long-day plants [petunia (Petunia ×hybrida Vilm.-Andr. ‘Dreams Midnight’) and snapdragon (Antirrhinum majus L. ‘Oh Snap Pink’)], short-day plants [african marigold (Tagetes erecta L. ‘Moonsong Deep Orange’) and potted sunflower (Helianthus annuus L. ‘Pacino Gold’)], and day-neutral plants [pansy (Viola ×wittrockiana Gams. ‘Matrix Yellow’) and zinnia (Zinnia elegans Jacq. ‘Magellan Cherry’)] were grown at 20/18 °C day/night air temperatures and under low (6–9 mol·m⁻²·d⁻¹) or high (16–19 mol·m⁻²·d⁻¹) seasonal photosynthetic DLIs from ambient solar radiation combined with supplemental high-pressure sodium lighting and DE LED lighting. Photoperiods consisted of a truncated 9-hour day (0800–1700 hr) with additional 1-hour (1700–1800 hr, 10 hours total), 4-hour (1700–2100 hr, 13 hours total), or 7-hour (1700–2400 hr, 16 hours total) R + W or R + W + FR LED lighting at 2 μmol·m⁻²·s⁻¹. Days to visible bud, plant height at first open flower, and time to first open flower (TTF) of each species were influenced by DLI, lamp type, and photoperiod though to different magnitudes. For example, plant height of african marigold and potted sunflower at first open flower was greatest under R + W + FR lamps, high DLIs, and 16-hour photoperiods. Petunia grown under R + W lamps, high DLI, and 10- and 13-hour photoperiods were the most compact. For all species, TTF was generally reduced under high DLIs. For example, regardless of the lamp type, flowering of african marigold occurred fastest under a high DLI and 10-hour photoperiod. Flowering of petunia and snapdragon occurred fastest under a high DLI, R + W + FR lamps, and a 16-hour photoperiod. However, only under high DLIs, R + W or R + W + FR lamps were equally effective at promoting flowering when used to provide DE lighting. Our data suggest that under low DLIs, flowering of long-day plants (petunia and snapdragon) occurs more rapidly under lamps providing R + W + FR, whereas under high DLIs, flowering is promoted similarly under either R + W or R + W + FR lamps.

Owen, W.G., Q. Meng, and R.G. Lopez. 2018. Promotion of flowering from far red radiation depends on the photosynthetic daily light. HortScience 53:1–7. https://doi.org/10.21273/HORTSCI12544-17

Propagation Daily Light Integral and Root-Zone Temperature Influence Rooting of Single-internode Pennisetum ×advena Culm Cuttings

Crown division, tissue culture, and culm cuttings are methods for propagating purple fountain grass [Pennisetum ×advena Wipff and Veldkamp (formerly known as Pennisetum setaceum Forsk. Chiov. ‘Rubrum’)]. However, propagation by culm cuttings is becoming an economically attractive method for quick liner production. Our objective was to quantify the impact of propagation daily light integral (PDLI) and root-zone temperature (RZT) on root and culm development of single-internode purple fountain grass culm cuttings. Before insertion into the rooting substrate, cuttings were treated with a basal rooting hormone solution containing 1000 mg·L⁻¹ indole-3-butyric acid (IBA) + 500 mg·L⁻¹ 1-naphthaleneacetic acid (NAA). The cuttings were placed in a glass-glazed greenhouse with an air temperature of 23 °C and benches with RZT set points of 21, 23, 25, or 27 °C. PDLIs of 4 and 10 mol·m⁻²·d⁻¹ (Expt. 1) or 8 and 16 mol·m⁻²·d⁻¹ (Expt. 2) were provided. After 28 d, culm and root densities (number) increased as the RZT increased from 21 to 27 °C, regardless of PDLI during Expt. 1. Compared with 4 mol·m⁻²·d⁻¹, a PDLI of 10 mol·m⁻²·d⁻¹ generally resulted in the greatest root biomass accumulation. For example, as PDLI increased from 4 to 10 mol·m⁻²·d⁻¹, root dry mass increased by 105%, 152%, and 183% at RZTs of 21, 25, and 27 °C, respectively. In Expt. 2, as the RZT increased from 21 to 23 °C, root dry mass increased by 70% under a PDLI of 8 mol·m⁻²·d⁻¹. However, root dry mass was similar among all RZTs under a PDLI of 16 mol·m⁻²·d⁻¹. Our results indicate that single-internode culm cuttings of purple fountain grass can be most efficiently propagated under PDLIs of 8–10 mol·m⁻²·d⁻¹ together with RZT set points of 23 to 25 °C for quick liner production.

Owen, W.G. and R.G. Lopez. 2018. Propagation daily light integral and root-zone temperature influence rooting of single-node Pennisetum ×advena culm cuttings. HortScience 53:176–182. https://doi.org/10.21273/HORTSCI12455-17

Geranium and Purple Fountain Grass Leaf Pigmentation Is Influenced by End-of-Production Supplemental Lighting with Red and Blue Light-emitting Diodes

Under low-light greenhouse conditions, anthocyanin pigmentation in vegetative tissues of red- or purple-leafed floricultural crops is not fully expressed and, consequently, plants are not as visually appealing to consumers. Our objective was to quantify the effect of end-of-production (EOP; before shipping) supplemental lighting (SL) of different light sources, qualities, and intensities on foliage color of geranium (Pelargonium ×hortorum L.H. Bailey ‘Black Velvet’) and purple fountain grass [Pennisetum ×advena Wipff and Veldkamp (formerly known as Pennisetum setaceum Forsk. Chiov. ‘Rubrum’)]. Plants were finished under early (Expt. 1) and late (Expt. 2) seasonal greenhouse ambient solar light and provided with 16 hours of day-extension lighting from low-intensity light-emitting diode (LED) lamps [7:11:33:49 blue:green:red:far-red light ratio (%); control] delivering 4.5 μmol·m⁻²·s⁻¹, or 16 hours of EOP SL from high-pressure sodium (HPS) lamps delivering 70 μmol·m⁻²·s⁻¹, or LED arrays (100:0, 87:13, 50:50, or 0:100 red:blue) delivering 100 μmol·m⁻²·s⁻¹, or 0:100 red:blue LEDs delivering 25 or 50 μmol·m⁻²·s⁻¹. Geranium and fountain grass chlorophyll content and leaf color were estimated using a SPAD-502 chlorophyll meter and Minolta tristimulus colorimeter, respectively. Relative chlorophyll content (RCC) and foliage L* (lightness), C* (chroma; a measure of saturation), and h° (hue angle; a measure of tone) values were significantly influenced by EOP SL and days of exposure. Generally, RCC of geranium and fountain grass increased from 3 to 14 days of exposure to EOP SL from HPS lamps and LEDs delivering 100 μmol·m⁻²·s⁻¹. Under low daily light integrals (DLIs) [8.6 mol·m⁻²·d⁻¹ (geranium) and 9.4 mol·m⁻²·d⁻¹ (purple fountain grass)] EOP SL providing 100 μmol·m⁻²·s⁻¹ of 100:0, 87:13, 50:50, or 0:100 red:blue light for ≥14 days resulted in lower L* (darker foliage), C* (saturated), and h° (orange to violet-red hues). Our data indicate that a minimum of 14 days of EOP SL providing 100 μmol·m⁻²·s⁻¹ of 50:50 or 0:100 red:blue light enhanced foliage color of geranium and fountain grass leaves when plants were grown under a low greenhouse DLI ≤ 9 mol·m⁻²·d⁻¹.

Owen, W.G. and R.G. Lopez. 2017. Geranium and purple fountain grass leaf pigmentation is influenced by end-of-production supplemental lighting with red and blue light-emitting diodes (LEDs). HortScience 52:236–244. https://doi.org/10.21273/HORTSCI11098-16

Late-season High Tunnel Planting of Specialty Cut Flowers in the Midwestern United States Influences Yield and Stem Quality

Production and market value of U.S. grown specialty cut flowers has increased over the past several years due to stem quality issues related to long-distance transport, regional proximity to market centers, and consumer’s willingness to purchase locally. Cut flowers are traditionally grown in field or greenhouse environments; however, high tunnels provide an alternative production environment and a number of cultural and economic advantages. Specialty cut flower species ‘Campana Deep Blue’ bellflower (Campanula carpatica), bells of ireland (Moluccella laevis), ‘Bombay Firosa’ celosia (Celosia cristata), ‘Amazon Neon Purple’ dianthus (Dianthus barbatus), ‘Fireworks’ gomphrena (Gomphrena pulchella), ‘Vegmo Snowball Extra’ matricaria (Tanacetum parthenium), and ‘Potomac Lavender’ snapdragon (Antirrhinum majus) were planted in both field and high tunnel environments during the late season (early summer) in the midwestern United States. Compared with field production, high tunnel production yielded 9.1 stems/m² (75%) for bells of ireland and 9.5 cm (15%), 16.8 cm (16%), 6.7 cm (44%), and 6.3 cm (19%) longer stems for bells of ireland, celosia, gomphrena, and matricaria, respectively. Additionally, stem length and caliper was greatest for high tunnel–grown bells of ireland, celosia, and dianthus. Our results indicate that late-season planting and production in a high tunnel is suitable for most of the species we investigated.

Owen, W.G., A. Hilligoss, and R.G. Lopez. 2016. Late-season high tunnel planting of specialty cut flowers in the Midwest influences yield and stem quality. HortTechnology 26:338–343. https://doi.org/10.21273/HORTTECH.26.3.338

Paclobutrazol Drench Activity Not Affected in Sphagnum Peat-based Substrates Amended with Pine Wood Chip Aggregates

Processed pine (Pinus sp.) wood has been investigated as a component in horticultural substrates (greenhouse and nursery) for many years. Specifically, pine wood chips (PWC) have been uniquely engineered/processed into a nonfiberous blockular particle size, suitable for use as a substrate aggregate. The purpose of this research was to determine if paclobutrazol drench efficacy is affected by PWC used as a substitute for perlite in a peat-based substrate. Paclobutrazol drench applications of 0, 1, 2, and 4 mg/pot were applied to ‘Pacino Gold’ sunflower (Helianthus annuus); 0.0, 0.25, 0.50, and 1.0 mg/pot to ‘Anemone Safari Yellow’ marigold (Tagetes patula); and 0.0, 0.125, 0.25, and 0.50 mg/pot to ‘Variegata’ plectranthus (Plectranthus ciliates) grown in sphagnum peat-based substrates containing 10%, 20%, or 30% (by volume) perlite or PWC. Efficacy of paclobutrazol drenches for controlling growth of all three species was unaffected by substrate composition. We concluded that substituting PWC for perlite as an aggregate in peat-based substrates should not reduce paclobutrazol drench efficacy, variability in PWC products indicates that efficacy should be tested before large-scale use. The variability results from wood components not being engineered and processed the same across manufacturers, meaning that they are often incapable of improving/influencing the physical and chemical behavior of a substrate similarly.

Owen, W.G., B.E. Jackson, B.E. Whipker, and W.C. Fonteno. 2016. Paclobutrazol drench activity not affected in sphagnum peat-based substrates amended with pine wood chip aggregates. HortTechnology 26:156–163. https://doi.org/10.21273/HORTTECH.26.2.156

Pine Wood Chips as an Alternative to Perlite in Greenhouse Substrates: Nitrogen Requirements

Processed pine wood (Pinus sp.) has been investigated as a component in greenhouse and nursery substrates for many years. Specifically, pine wood chips (PWC) have been uniquely engineered/processed into a nonfiberous blockular particle size, suitable for use as a substrate aggregate. In container substrates, nitrogen (N) tie-up during crop production is of concern when substrates contain components with high carbon (C):N ratios, like that of PWC that are made from fresh pine wood. The objective of this research was to compare the N requirements of plants grown in sphagnum peat–based substrates amended with perlite or PWC. Fertility concentrations of 100, 200, or 300 mg·L⁻¹ N were applied to ‘Profusion Orange’ zinnia (Zinnia ×hybrida) and ‘Moonsong Deep Orange’ marigold (Tagetes erecta) grown in sphagnum peat–based substrates containing 10%, 20%, or 30% (by volume) perlite or PWC. Zinnia plant substrate solution electrical conductivity (EC) was not influenced by percentage of perlite or PWC. Perlite-amended substrates fertilized with 200 mg·L⁻¹ N for growing zinnia, maintained a constant EC within optimal levels of 1.0 to 2.6 mS·cm⁻¹ from 14 to 42 days after planting (DAP), and then EC increased at 49 DAP. In substrates fertilized with 100 and 300 mg·L⁻¹ N, EC levels steadily declined and then increased, respectively. Zinnia plants grown in PWC-amended substrates fertilized with 200 mg·L⁻¹ N maintained a constant EC within the optimal range from 14 to 49 DAP. Marigold substrate solution EC was only influenced by N concentration and followed a similar response to zinnia substrate solution EC. Zinnia and marigold substrate solution pH was influenced by N concentration and generally decreased with increasing N concentration. Plant growth and shoot dry weight were similar when fertilized with 100 and 200 mg·L⁻¹ N. According to this study, plants grown in PWC-amended substrates fertilized with 100 to 200 mg·L⁻¹ N can maintain adequate substrate solution pH and EC levels and sustain plant growth with no additional N supplements. Pine wood chips are engineered and processed to specific sizes and shapes to be functional as aggregates in a container substrate. Not all wood components are designed or capable of improving/influencing the physical and chemical behavior of a substrate the same. On the basis of the variability of many wood components being developed and researched, it is suggested that any and all substrate wood components not be considered the same and be tested/trialed before large-scale use.

Owen, W.G., B.E. Jackson, B.E. Whipker, and W.C. Fonteno. 2016. Pine wood chips as an alternative to perlite in greenhouse substrates: nitrogen requirements. HortTechnology 26:199–205. https://doi.org/10.21273/HORTTECH.26.2.199

End-of-production Supplemental Lighting with Red and Blue Light-emitting Diodes (LEDs) Influences Red Pigmentation of Four Lettuce Varieties

Under low-light greenhouse conditions, such as those found in northern latitudes, foliage of red leaf lettuce (Lactuca sativa L.) varieties is often green and not visually appealing to consumers. Our objective was to quantify the effect of end-of-production (EOP; prior to harvest) supplemental lighting (SL) of different sources and intensities on foliage color of four red leaf lettuce varieties, ‘Cherokee’, ‘Magenta’, ‘Ruby Sky’, and ‘Vulcan’. Plants were finished under greenhouse ambient solar light and provided with 16-hours of day-extension lighting from low intensity light-emitting diode (LED) lamps [7:11:33:49 blue:green:red:far red (control)] delivering 4.5 μmol·m⁻²·s⁻¹, or 16-hours of EOP SL from high-pressure sodium (HPS) lamps delivering 70 μmol·m⁻²·s⁻¹, or LED arrays [100:0, 0:100, or 50:50 (%) red:blue] delivering 100 μmol·m⁻²·s⁻¹, or 0:100 blue LEDs delivering 25 or 50 μmol·m⁻²·s⁻¹. Relative chlorophyll content (RCC) and foliage L* (lightness), and chromametric a* (change from green to red) and b* (change from yellow to blue) values were significantly influenced by EOP SL and days of exposure. Generally, RCC of all varieties increased from day 3 to 14 when provided with EOP SL from the HPS lamps and LEDs delivering 100 μmol·m⁻²·s⁻¹. End-of-production SL providing 100 μmol·m⁻²·s⁻¹ of 100:0, 0:100, or 50:50 red:blue light for ≥5 days resulted in increasing a* (red) and decreasing L* (darker foliage), b* (blue), and h° (hue angle; a measure of tone) for all varieties. Our data suggests that a minimum of 5 days of EOP SL providing 100 μmol·m⁻²·s⁻¹ of 100:0, 0:100, or 50:50 red:blue light enhanced red pigmentation of ‘Cherokee’, ‘Magenta’, ‘Ruby Sky’, and ‘Vulcan’ leaves when plants are grown under a low greenhouse daily light integrals (DLIs) <10 mol·m⁻²·d⁻¹.

Owen, W.G. and R.G. Lopez. 2015. End-of-production supplemental lighting with red and blue light-emitting diodes (LEDs) influences red pigmentation of four lettuce varieties. HortScience 50:676–684. https://doi.org/10.21273/HORTSCI.50.5.676