Search Results

Domestic production of culinary herbs continues to increase in the United States. Culinary herbs are primarily propagated by seed; however, some herbs have poor germination rates and slow growth. Thus, there are advantages of propagating herbs by vegetative stem-tip cuttings as they lead to true-to-type plants and a shortened production time. Previous research of ornamental young plants and finished culinary herbs have shown a reduction in rooting time and increases in plant quality with increases in the photosynthetic daily light integral (DLI). To our knowledge, little to no research has addressed how the DLI influences culinary herb liner quality. Therefore, the objectives of this study were to quantify morphological traits of five economically important culinary herbs when grown under DLIs ranging from 2.8 to 16.4 mol·m⁻²·d⁻¹. Stem-tip cuttings of Greek oregano (Origanum vulgare var. hirtum), rosemary ‘Arp’ (Rosmarinus officinalis), sage ‘Extrakta’ (Salvia officinalis), spearmint ‘Spanish’ (Mentha spicata), and thyme ‘German Winter’ (Thymus vulgaris) were excised from stock plants and rooted under no shade or aluminum shading of 36%, 56%, or 76% to create a range of DLI treatments. After 9 days (spearmint) or 16 days (all other genera) of DLI treatments, the root, shoot, and total dry mass of all culinary herb liners generally increased by 105% to 449%, 52% to 142%, and 82% to 170%, respectively, as the DLI increased from 2.8 to 16.4 mol·m⁻²·d⁻¹ or genus-specific DLI optimums. Stem length of oregano, spearmint, and thyme decreased by 37%, 28%, and 27%, respectively, as the DLI increased from 2.8 to 16.4 mol·m⁻²·d⁻¹. However, stem length of rosemary and sage were unaffected by the DLI. The quality index of all genera was greatest at DLIs from 10.4 to 16.4 mol·m⁻²·d⁻¹. Furthermore, all culinary herbs grown under a DLI of ≤6 mol·m⁻²·d⁻¹ had low root and shoot dry mass accumulation; and oregano, spearmint, and thyme were generally taller. Therefore, DLIs between 10 to 12 mol·m⁻²·d⁻¹ should be maintained during culinary herb propagation, because a DLI ≥16 mol·m⁻²·d⁻¹ may be deleterious and energy inefficient if supplemental lighting use is increased.

Chrysanthemum (Chrysanthemum ×morifolium) is a common ornamental crop with a qualitative short-day flowering response. Extending a short day with moderate blue [B (400–500 nm)] light inhibits flowering in greenhouse conditions with sunlight but does not indoors (without sunlight) under B + red [R (600–700 nm)] light or white light. We postulated that the contrasting responses to B light as a day extension depended on far-red [FR (700–800 nm)] light during the day, which is plentiful under sunlight but lacking indoors under B+R or white light-emitting diodes. To study this response in three chrysanthemum cultivars, we delivered indoor lighting treatments at two locations with an 11-hour main photoperiod of B, green [G (500–600 nm)], R, and FR light, where subscript values indicate the photon flux density (in µmol·m⁻²·s⁻¹) of each waveband: B₆₀R₁₂₀, B₆₀G₆₀R₆₀, and B₆₀R₆₀FR₆₀. After each short main photoperiod, plants received 0 or 4 hours of day-extension lighting of 60 µmol·m⁻²·s⁻¹ of B light (B₆₀). Under all treatments except B₆₀R₆₀FR₆₀ with day-extension B₆₀, it took ‘Chelsey Pink’, ‘Gigi Gold’, and ‘Gigi Yellow’ 13 to 17 days to reach the first visible inflorescence and 42 to 51 days to the first open flower. In contrast, plants grown under B₆₀R₆₀FR₆₀ with day-extension B₆₀ took 41 to 67 days to reach the first visible inflorescence with few plants developing open flowers. Plants were tallest at the first open flower and after 9 weeks of treatments when grown under B₆₀R₆₀FR₆₀ with day-extension B₆₀. These results indicate that the inclusion of FR light, but not G light, in the main photoperiod is necessary for day-extension B light to inhibit flowering in chrysanthemum. On the basis of these results and those of other studies, we postulate that the spectral dependence of flowering in chrysanthemum depends on whether and how the phytochrome photoequilibrium changes during the day. In particular, a sufficiently high daytime phytochrome photoequilibrium (e.g., under B+R and B+G+R light) could establish a predominant mode of floral signaling that prevents perception of subsequent B light as a long day.