Reducing Substrate Moisture Content during Greenhouse Production of Poinsettia Improves Postproduction Quality and Economic Value

Abstract

The objective was to determine the effect of substrate moisture content (SMC) during poinsettia (Euphorbia pulcherrima) greenhouse production on plant quality, postproduction longevity, and economic value. Two experiments were conducted, one in 2016 with ‘Freedom Red’ and the other in 2017 with ‘Christmas Eve Red’. Treatments included two SMC levels (20% or 40%) applied in four timing of application combinations. Total production (TP) time was 14 (2016) or 12 (2017) weeks in which vegetative production (VP) occurred from week 33 (2016) or 35 (2017) to week 39 and reproductive production (RP) continued from week 40 to 47. The four timing of application treatments were 40/40 = TP at 40% SMC; 20/40 = VP at 20% + RP at 40%; 40/20 = VP at 40% + RP at 20%; 20/20 = TP at 20% SMC. After simulated shipping in the dark, plants were evaluated in a simulated retail environment with two packaging treatments: no sleeve covering or plastic perforated plant sleeves covering container and plant. At the end of greenhouse production, plants grown in 20% SMC during RP (20/20 and 40/20) had shorter bract internode length, stem length, and smaller growth index (GI), decreased shoot and root dry weight (DW), and bract and leaf surface area compared with those in 40% SMC during RP (40/40 and 20/40). Photosynthetic rate was higher when plants were watered at 40% SMC regardless of production stage compared with those in 20% SMC. Leaf thickness, petiole thickness, total bract and leaf number were unaffected by SMC treatments. Plants in 20% SMC during RP (20/20 or 40/20) had earlier bract coloring despite days to anthesis being the same for all SMC treatments. Compared with 40/40, 40/20, and 20/20 could save 44.2% or 43.6%, respectively, irrigation and fertilizer usage, and 39.1% and 47.8%, respectively, labor time. During postharvest, ethylene concentration was unaffected by packaging method. Sleeved plants, regardless of SMC treatment, received lower light intensity in the middle of the plant canopy, causing plants to have lower total leaf number due to abscission and SPAD reading at the end of postproduction. The 40/40 treatment abscised more bracts during five weeks (in 2016) of postproduction and with no sleeve had higher number of bracts with bract edge burn (BEB). In summary, reducing SMC to 20% during TP or RP reduced water usage during production and produced more compact plants with increased postproduction quality.