2018 ASHS Annual Conference

The objective was to determine the effect of substrate moisture content (SMC) during poinsettia (Euphorbia pulcherrima ‘Christmas Eve Red’) greenhouse production on plant quality, postproduction longevity and economic value. Treatments included two SMC levels (20% or 40%) applied in four timing of application combinations. Total production (TP) time was 12 weeks in which vegetative production (VP) occurred from week 35 to 39 and reproductive production (RP) continued from week 40 to 47. Four timing of application treatments: 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 12 h simulated shipping in the dark, plants were evaluated for two weeks in a simulated retail environment with two packaging treatments: no packaging or plastic perforated plant sleeves. Growth index (GI), photosynthesis (Pn) and water potential were measured weekly. Bract and leaf surface area, bract and leaf number, internode length, leaf thickness, flower and bud number, petiole thickness and dry weight (DW) were measured at week 47. Light intensity within the plant canopy and ethylene concentration were measured during postproduction. Water potential was reduced in week 40 with 40/20 treatment only. At the end of greenhouse production, plants gown in 20% SMC during RP (20/20 and 40/20) had shorter bract internode length, stem length and smaller GI, and decreased shoot and root DW, and bract and leaf surface area compared to those in 40% SMC during RP (40/40 and 20/40). Poinsettias grown in 40% SMC had higher Pn than those in 20% SMC regardless of production stage. Leaf thickness, petiole thickness, bract and leaf number were not affected by SMC treatments. Plants in 20/20 or 40/20 had earlier bract coloring despite days to anthesis being the same for all SMC treatments. Compared to 40/40, 40/20 and 20/20 could save 44.2% or 43.6%, respectively, on irrigation and fertilizer usage, and 39.1% and 47.8%, respectively, on labor time. During postharvest, ethylene concentration was not affected by packaging method. Sleeved plants had lower light intensity in the plant canopy causing plants to have greater necrotic stem numbers and lower visual ratings at the end of postproduction. The 40/40 sleeved plants had increased yellow leaf and necrotic stem numbers. In summary, reducing SMC to 20% during total production or during the reproductive stage reduced water usage and produced more compact plants with greater postproduction quality.