Two application methods of calcium (Ca), fertigation and spray, were investigated regarding their effects on Botrytis blight on petunia (Petunia ×hybrida) flowers. Plants were grown for 6 weeks with three nutrient solutions consisting of 0, 100, or 200 mg·L−1 Ca and weekly calcium chloride (CaCl2) sprays of 0, 750, or 1500 mg·L−1 Ca for a total of nine treatment combinations. Flowers were harvested, inoculated with Botrytis spores, placed in humidity chambers, and evaluated for Botrytis blight severity. Disease severity decreased by 57% and 70% when flowers were treated with Ca spray applications of 750 and 1500 mg·L−1 Ca, respectively; however, no change in disease severity occurred across the Ca fertigation applications. Ca concentration in the flower petal tissue increased with the Ca spray applications: the flower petal Ca concentration increased from 0.26% to 0.65% of tissue dry mass (DM) as the Ca spray application rate increased from 0 to 1500 mg·L−1. However, no change was observed across the Ca fertigation treatments. Leaf tissue Ca concentration increased from 2.1% to 3.2% DM as the fertigation solution increased from 0 to 200 mg·L−1 Ca, whereas spray application had no significant effects of leaf tissue Ca concentration. The results demonstrate that spray application is a more effective technique than fertigation application to provide higher Ca tissue concentrations in flowers, and that the Ca concentration in flower petal tissue is an important consideration when evaluating tissue susceptibility to Botrytis blight. Because of the high rate of fungicide resistance to Botrytis cinerea found in commercial greenhouses, spray applications of CaCl2 are an important disease management tool for commercial growers.

Herbaceous stock plant production and cutting harvest methods affect the performance of cuttings harvested from those stock plants. Specifically, the effect of daily light integral (DLI), ethephon spray applications, and the stock plant node position (NPSP) of hybrid impatiens (Impatiens ×hybrida) ‘Compact Electric Orange’ stock plants on the flowering of the harvested cuttings was examined. The DLI treatments were grouped in ranges of low (5.1–5.5 mol·m–2·d–1), medium (7.6–8.8 mol·m–2·d–1), and high (10.3–12.0 mol·m–2·d–1) levels. The stock plants were treated weekly with 0, 50, 100, 200, or 300 mg·L–1 ethephon. Cuttings were harvested from six NPSP, which refers to the location on the stock plants from which the cuttings were harvested. Time to flower of the harvested cuttings decreased as DLI increased from 5.1 to 12.0 mol·m–2·d–1, as ethephon concentrations decreased from 300 to 0 mg·L–1, and as NPSP moved from lower to upper positions within the stock plant canopy. Time to flower was highly correlated with the node position on the cutting (NPC) where the first flower appeared. For example, when flowers appeared in the lowest NPC on the shoot (NPC 1), the first flower opened 2.5 weeks after sticking the unrooted cuttings in propagation, while flowers that appeared in NPC 7, the seventh-oldest node from the base of the cutting, opened at 9.0 weeks. The results demonstrate how stock plant management practices can be manipulated to produce cuttings that allow growers to produce flowering plants on different schedules, i.e., production time can be shortened from conventional production schedules, which may allow hybrid impatiens to be marketed like bedding plant species such as impatiens (Impatiens walleriana).

The effect of average daily temperature (ADT) on flower bud development and subsequent time to flower was investigated on hybrid impatiens (Impatiens ×hybrida) cultivars Compact Electric Orange, Compact Hot Coral, and Compact Orchid Blush. Plants with a visible flower bud measuring 2 mm in width were placed in one of the four greenhouses with temperature setpoints ranging from 16 to 28 °C. Flower bud width was measured every 3 days in each ADT treatment until flowering. The subsequent days to flower (DTF) from the onset of a visible bud decreased from 36 to 27 days as the ADT increased from 17 to 28 °C. The DTF from visible bud varied by <3 days among the three cultivars across all temperatures; therefore, cultivar data were pooled to create a stronger prediction model. A logistic formula was used to predict the remaining DTF as a function of flower bud width and ADT. The model accurately described the effect of bud width and ADT on flowering time within ±3 days for 87% of the actual DTF across all three cultivars. The resulting flower development model provides greenhouse growers with a guide for manipulating temperature to produce flowering plants for specific market dates based on flower bud width measurements.