EFFECTS OF PLANTING DATE AND ENVIRONMENT ON THE CUT FLOWER PRODUCTION OF SANTONIA 'GOLDEN LIGHTS'

Abstract

The effects of two growing environments (a glasshouse and a sheltered outdoor site) and four planting dates (11 October and 22 November 2000, 3 January and 14 February 2001) on the cut flower production of Santonia ‘Golden Lights’ were assessed. Stem length, stem strength, flower colour and tuber weight were affected by growing environment and planting date. Stem length on outdoor grown plants was reduced by 280 mm, stem strength was improved and there was some reddening of flowers, but the number of flowers/stem was not affected. Results suggest that when Santonia is grown under suitable environmental conditions, stems that are acceptable as cut flowers can be produced. INTRODUCTION Sandersonia aurantiaca (Hook.) has been developed over the last 20 years by growers and researchers in New Zealand as a successful cut flower crop with export receipts of NZ$2.6M in 2002 (HortResearch, 2002). Countries such as Japan and South Africa are now producing Sandersonia so new cultivars are needed if New Zealand is to maintain its market share. The new hybrid Santonia ‘Golden Lights’ was released in 1998 by Sanza Ltd in New Zealand. It is a Sandersonia aurantiaca x Littonia modesta F1 hybrid (Morgan et al., 2001). With its ability to rapidly produce large tubers that produce long stems with a number of laterals and leaves with small tendrils, Santonia ‘Golden Lights’ was initially envisaged for the nursery market as a climber. Preliminary studies have indicated that in cooler conditions it may be possible to produce stems with the length, strength, flower colour and vase life to make Santonia suitable as a cut flower (Morgan et al., 2003; Eason et al., 2001). Studies on Sandersonia have shown that the time of planting and growing environment affect stem length and tuber production (Clark, 1994, 1995; Clark and Burge, 1997; Clark and Reyngoud, 1997). The objective of this study was to examine the effects of planting date and environment on Santonia ‘Golden Lights’ to determine whether production systems could be developed to produce cut flower stems of export quality. MATERIALS AND METHODS The effects of two growing environments (a glasshouse and an outdoor site sheltered with wind break cloth) and four planting dates at six-week intervals (11 October and 22 November 2000, 3 January and 14 February 2001) on cut flower production were assessed in a randomised block design with four replicates. Both growing sites were at the Pukekohe Research Centre, Pukekohe, New Zealand. At the first planting date a line of 10-15 g Santonia tubers that had been stored at 5°C for 4-5 months was assigned at random to one of four planting dates. The three groups assigned to later planting dates were transferred into three polystyrene boxes (100/box) where they were placed between layers of newspaper then returned to storage at 3°C (Morgan et al., 2003). Proc. IX Intl. Symp. on Flower Bulbs Eds.: H. Okubo, W.B. Miller and G.A. Chastagner Acta Hort. 673, ISHS 2005 266 On each planting date, a box was placed into a thermostatically controlled incubator at 20°C for 7 days to pre-sprout the tubers (Clark, 1994). The tubers were then divided and graded to give an even line of single growing point tubers for each replicate. Owing to losses in storage and non-viable growing points, the tuber numbers/replicate for plantings 1-4 were 22, 19, 19 and 12 respectively, with mean planted tuber weights of 6.1, 6.0, 5.5 and 6.0 g. Tubers were dipped in a fungicide mixture containing 0.5 g/litre benomyl and 2.0 g/litre thiram for 10 min prior to planting into polystyrene trays (595 x 420 x 190 mm) containing 25 litres of commercial (Yates NZ Ltd) nitrogen stabilised composted radiata pine bark fines (0-8 mm) with incorporated fertilisers. At planting, the water soluble nutrient content of the bark medium was measured in a 1:1.5 media:water (v:v) extract using colorimetry and atomic absorption methods. Media nutrient levels were pH 5.3, Ca 68 ppm, K 63 ppm, P 19 ppm, Mg 43 ppm and N 70 ppm. All trays were mulched with 10 mm of sawdust. The crop was supported with netting and watered daily at a rate of 2.5 litres/m. The glasshouse was unheated and vented at 25°C. Air temperatures were measured at 500 mm above soil level, soil temperatures at a depth of 75 mm, and both were logged at 1 min intervals using a Campbell CR10 data logger. Daily solar radiation (MJ/m) was recorded by a National Institute of Weather and Atmospheric Research automatic weather station sited 100 m away from both growing environments. The stems were harvested just above the second leaf when the second flower had reached anthesis. Harvest date, stem length and weight, the number of laterals, flower number/stem and per lateral, flower size (length and width), stem strength and flower colour (Table 1) were measured. For all treatments, watering was stopped 18 weeks after planting, and tubers were lifted and weighed 2 weeks later. Data were analysed using analysis of variance (GENSTAT 2002). RESULTS AND DISCUSSION The time to flower harvest was significantly (P=0.002) affected by both planting date and environment (Table 2). It was, on average, 13 days longer for the tubers planted outdoors than for those in the glasshouse. This period gradually decreased over the first three planting dates before increasing for the fourth. This pattern matched changes in mean temperature during the season (Table 9). Similar seasonal patterns of flower harvest times have been found in Sandersonia (Clark, 1994, 1995; Clark and Reyngoud, 1997). Davies et al. (2002a) found a strong correlation between temperature and the time to flower harvest in Sandersonia in controlled environment studies. There was a significant interaction between planting date and growing environment (P=0.001) on stem length. Stems were on average 280 mm longer in the glasshouse than outdoors. Stems were longest for planting times 1 and 2 in the glasshouse and shortest for the outdoor planting at time 2 (Table 3). Internode and stem length in many ornamental plants increase with increasing DIF (day/night temperature differential) (Moe and Heins, 1990). Although Sandersonia stems were shorter in greenhouses in the hot summer months, they were still longer than stems produced by plants grown outdoors (Clark, 1994; Clark and Reyngoud, 1997). Controlled environment studies with Sandersonia have found that stem length increases at temperatures up to 24°C, at low light intensities and at higher DIF (Davies et al., 2002a, b). Stem length of Santonia is probably influenced by an interaction of these three factors. It was cooler outdoors than in the glasshouse (Table 9). Outdoor DIF values (Table 9) would have been less than glasshouse values as daily maximum glasshouse temperatures are on average 3-5°C greater than ambient in the best ventilated greenhouses and drop to ambient outdoor temperatures at night. Light intensities were 22% higher outdoors in January than in the glasshouse (measured using a Licor quantum sensor). These factors would reduce stem length outdoors compared to the glasshouse, and combine to produce the longest stems in the glasshouse and the shortest stems outdoors from planting date 2. This would suggest that a DIF value of 8.0-9.0°C is optimal for Santonia production.