Although effects of R:FR ratios have been studied to a limited extent in poinsettia, experiments where poinsettia plants were covered by selective films absorbing FR or R light, indicated that morphology is affected by the R:FR ratio
Also, when a greenhouse-grown poinsettia cultivar was provided with a 30 min EOD-R treatment plant height was reduced compared to those where only high pressure sodium (HPS) lamps were used as supplementary light in addition to natural light
Plant growth regulators (PGRs) such as chlormequat, daminozide or paclobutrazol are commonly used in this respect to control shoot elongation.
However, due to the potentially negative effects of PGRs on human health and the environment their use is becoming restricted and desirable to phase out.
In addition, application of PGRs is time-consuming. In northern areas temperature drop treatments in the morning are commonly used in combination with PGRs to reduce elongation growth.
However, use of such temperature drops is limited by periods of high temperatures and high solar radiation in early autumn as well as energy-saving regimes in semi-closed or closed greenhouses.
As an alternative, exploiting the responses of the plants to different light qualities provides an interesting possibility in greenhouse production of poinsettia