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To clarify detailed patterns of responses to blue light associated with decreasing phytochrome activity, the growth and morphology traits of arugula, cabbage, mustard, and kale microgreens were compared under the treatments: (1) R, pure red light; (2) B, pure blue light; (3) BRF0, (4) BRF2, (5) BRF4, and (6) BRF6: unpure blue lights created by mixing B with low-level (6%) R, and further adding 0, 2, 4, and 6 μmol m−2 s−1 of far-red light, respectively. The calculated phytochrome photostationary state (PPS) value, indicating phytochrome activity, gradually decreased in the order of R (0.89), BRF0 (0.69), BRF2 (0.65), BRF4 (0.63), BRF6 (0.60), and B (0.50). Generally, the elongation growth (including stem extension rate, hypocotyl length, or petiole length) under blue lights increased with the decreasing PPS values, showing the highest and lowest sensitivity for arugula and mustard, respectively. However, the elongation promoted by blue lights gradually became saturated once the PPS values decreased below 0.60, a level which deactivates phytochrome. Other plant traits, such as biomass allocation and plant color, varied with increasing shade-avoidance responses to blue lights with decreasing PPS values relative to R, and these traits reached saturation at a similar PPS value as elongation. The response sensitivity was highest in elongation growth for arugula and cabbage, and highest in plant color for kale and mustard. This suggests that deactivated phytochrome contributes to the maximum elongation promotion as a shade-avoidance response induced by blue light, although the response sensitivity varies with plant traits and species.

To explore the action mode of blue light on elongation growth of microgreens, the growth and morphology traits of arugula (Brassica eruca L., ‘Rocket’), cabbage (Brassica oleracea, unknown variety name), mustard (Brassica juncea, ‘Ruby Streaks’), and kale (Brassica napus, ‘Red Russian’) seedlings were compared under four light quality treatments: (1) R, “pure” red light (660 nm); (2) B, “pure” blue light (450 nm); (3) BU, “unpure” blue light created by mixing B with a low level of UVA (≈7.5% photosynthetic photon flux); and (4) BF, “unpure” blue light created by mixing B with a low level of far-red light (≈ 10% photosynthetic photon flux). Continuous (24-hour) light-emitting diode lighting with either 100 or 50 μmol m−2·s−1 photosynthetic photon flux density at ≈ 23 ℃ was used with the above treatments. After 11 to 14 days of light treatment, B vs. R promoted elongation growth as demonstrated by a greater stem extension rate, hypocotyl length, or petiole length in the tested microgreen species, except for mustard. The promotion effects on elongation were stronger under lower vs. higher light for cabbage and kale, and cotyledon size was also reduced by B vs. R light in most cases, which suggested that stem elongation under pure blue light appeared to be one of the shade-avoidance responses in de-etiolated seedlings. BU vs. B inhibited elongation growth for some species at 100 μmol m−2·s−1 in most cases, but BU vs. R did not, except for mustard at 50 μmol m−2·s−1. BF vs. B increased stem extension rate, and hypocotyl length for arugula and mustard, and petiole length for arugula, but not in other cases. If considering all plant traits together using principle component analysis, BU and BF effects were similar to B, but different from R. This suggests that after adding UVA or far-red light, the pure blue light effects on growth and morphology are slightly changed, with varying sensitivity among species.

A greenhouse study was undertaken to investigate whether light-emitting diode (LED) technology can be used to replace high-pressure sodium (HPS) lighting for cut gerbera production during Canada’s traditional supplemental lighting (SL) season (November to March). The study was carried out at the University of Guelph’s research greenhouse, using concurrent replications of SL treatments within the same growing environment. LED (85% red, 15% blue) and HPS treatment plots were set up to provide equal amounts of supplemental photosynthetically active radiation (PAR) at bench level. This setup was used to assess the production of three cultivars of cut gerbera (Gerbera jamesonii H. Bolus ex Hook.f): Acapulco, Heatwave, and Terra Saffier. There were no treatment differences in SL intensity, with average SL photosynthetic photon flux density (PPFD) and daily light integral (DLI) of 55.9 µmol·m−2·s−1 and 2.3 mol·m−2·d−1, respectively. Flowers harvested from the LED treatment had a 1.9% larger flower diameter in ‘Acapulco’; 4.2% shorter and 3.8% longer stems in ‘Heatwave’ and ‘Terra Saffier’, respectively; and 7.7% and 8.6% higher fresh weights for ‘Acapulco’ and ‘Terra Saffier’, respectively, compared with flowers harvested from the HPS treatment. There were no differences in accumulated total or marketable flower harvests for any of the cultivars. The vase life of ‘Acapulco’ flowers grown under the LED treatment was 2.7 d longer than those grown under the HPS treatment, but there were no SL treatment effects on water uptake for any of the cultivars during the vase life trials. There were no SL treatment effects on specific leaf area for any of the cultivars. There were only minimal treatment differences in leaf, soil, and air temperatures. Cut gerbera crops grown with under LED SL had equivalent or better production and crop quality metrics compared with crops grown under HPS SL.

There is a potentially large market for locally produced organic bitter melons (Momordica charantia L.) in Canada, but it is a great challenge to grow this warm-season crop in open fields (OFs) due to the cool and short growing season. To test the feasibility of using high tunnels (HTs) for organic production of bitter melons in southern Ontario, plant growth, fruit yield and quality, and pest and disease incidence were compared among three production systems: OF, HT, and high tunnel with anti-insect netting (HTN) at Guelph in 2015. The highest marketable fruit yield was achieved in HTN (≈36 t·ha−1), followed by HT (≈29 t·ha−1), with the lowest yield obtained in OF (≈3 t·ha−1). Compared with OF, there were several other benefits for bitter melon production in HT and HTN: increased plant growth, advanced harvest timing, reduced pest numbers and disease incidence, and improved fruit quality traits such as increased individual fruit weight and size, and reduced postharvest water loss. In addition to higher yield, HTN had fewer insect pests and disease incidence compared with HT. The results suggest that HTs can be used for organic production of bitter melon in southern Ontario and regions with similar climates. Also, the addition of anti-insect netting to HTs is beneficial to production if combined with an effective pollination strategy.