ASHS 2024 Conference

Propagation greenhouses produce a wide range of crops, each presenting unique responses to light quality and quantity. With dynamic LED lighting solutions now available and proven to be viable over large acreages, propagators can tailor their lighting protocols to each crop with regards to zone management, photoperiod, spectrum and intensity. The effects of light quality and quantity on plant morphology and growth are well documented and while the exact impact is not generalizable across all crops and varieties, certain themes hold true. For example, high levels of blue light are generally associated with compact plants and thick, waxy leaves. In contrast, high levels of far-red light can cause etiolation in multiple species through the shade avoidance response but enhances photosynthesis and growth when combined with red light. Given the high importance of crop morphology in propagation, dynamic Dynamic LED lighting has been used to develop advanced lighting protocols in the propagation of fruit, vegetable and ornamental crops. In the production of cucumber transplants, applying high levels of blue light and a long photoperiod effectively slows the growth of cucumber transplants at the end of the propagation cycle, a strategy which proved useful to a propagator looking to delay transplant delivery per the client’s request. Concretely, the combination of high blue levels and a long photoperiod slowed crop growth, prevented tendril development and restricted plant stretching. Further, the use of high-blue treatments over young leafy greens effectively reduced plant height by 2-3 cm and produced stronger plants. Another trial focused on the production of strawberry tray plants found that a balanced light spectrum produced more stolons (i.e., daughter plants) while a blue-enriched spectrum produced significantly more leaves. In the production of ornamentals, dynamic lighting can be used to reduce the greenhouse’s reliance on plant growth regulators (PGRs), enhance leaf or petal coloration and trigger bud formation. In red-leafed varieties, controlled light-induced plant stress through spectral and/intensity adjustments have proven effective at stimulating the production of red pigments and enriching the leaves’ hue. Results from various commercial and research trials demonstrate benefits of dynamic LED lighting in the propagation of horticultural and ornamental crops alike. This presentation presents data from the aforementioned case studies among others.