Narrow-band lighting combined with short photoperiods as a way to control growth and shape in greenhouse grown ornamentals

The use of plant growth retardants for greenhouse grown ornamentals is increasingly restricted by regulations in many countries.
Growers are searching for alternative methods for controlling and restricting growth of pot- and bedding plants.
Manipulation of the photoperiod by blackout screens and light quality by adding narrow-band light from LEDs is one way of controlling growth.
Different pot- and bedding plants, Pelargonium, Calibrachoa, Tagetes and Argyranthemum, were grown using short photoperiods (8 h) in combination with periods of narrow-band lighting applied before, after or during the period of natural light.
As control treatments, we used plants grown in natural day length supplied with light from HPS-fixtures to the same DLI as the treatments, with or without chemical growth control.
Results showed that a light program with 2 h 620 nm light pre-day, 8 h of natural daylight supplemented with 660 nm light and a 2 h end-of-day treatment with 525 nm light was as effective as chemical growth control in reducing plant height and stem elongation.
However, the number of flowers was lower for Argyranthemum and flowering was somewhat delayed in Argyranthemum and Tagetes.

International Symposium on New Technologies and Management for Greenhouses – GreenSys2015

K.-J. Bergstrand, H. Asp, H.K. Schüssler

Argyranthemum, Calibrachoa, growth regulation, Pelargonium, Tagetes

https://doi.org/10.17660/ActaHortic.2017.1170.119