Postharvest Decline in Simulated Shipping and Retail Environments
Shipping distances and times are continuing to become longer, and how well plants hold up after shipping has never been more important. The objective of this research was to simulate shipping for zero, one or two days to determine qualitative and quantitative shelf-life longevity of 21 cultivars of cool- and warm-season vegetative annuals, determine the effect of shipping duration and characterize postharvest decline symptoms. This study was designed to lead to further investigation of production methods and postproduction environment parameters to increase postharvest longevity of vegetative annual garden plants grown in small containers.
Cool-Season Vegetative Annuals
Plant cultivars included argyranthemum 'Comet White' and 'Sunlight' or marguerite daisy (Argyranthemum frutescens); calibrachoa 'Liricashowers Deep Blue Imp', 'Starlette Trailing Purple' and 'Superbells Trailing Blue'; diascia 'Sun Chimes Coral'; nemesia 'Aromatica White' and 'Vanilla Sachet'; and sutera 'Bridal Showers' and 'Candy Floss Blue' (Sutera hybrida). All were planted in soilless media in 4_-inch geranium pots. Plants were hand-watered with reverse osmosis water and fertilized each time they were irrigated.
Warm-Season Vegetative Annuals
Plant cultivars included angelonia 'Caritas Lavender' (Angelonia angustifolia); strawflower or bracteantha 'Dreamtime Copper', 'Dreamtime Cream', 'Florabella White', 'Florabella Gold', 'Sundaze Bronze' and 'Sundaze Golden Yellow'; lantana 'Lucky Lemon Cream' and 'Lucky Peach Sunrise' (Lantana camara); and petunia 'Cascadias Pink' and 'Suncatcher Pink'. Pot size depended on growth habit of the cultivar and included 4_-inch geranium pots, 5-inch azalea pots or 4_-inch azalea pots. Plants were watered by hand and fertilized each time they were irrigated.
Shipping and Postharvest Treatments and Evaluation
The three shipping durations used were zero, one or two days. Simulated shipping was in a dark growth chamber at 80¡ F. A postship flower number was counted, and quality ratings were assigned to each plant as they were moved from simulated shipping.
Simulated shelf life was in a growth room at 70¡ F with an average light intensity of 30 foot-candles. Lights were turned on from 8 a.m. to 5 p.m., for a nine-hour photoperiod. Plants were watered by hand with plain water during the three weeks they remained in the growth room. Flower number and quality rating were recorded weekly for each termed postharvest time of measurement.
The plant quality rating was assessed on a point scale of zero to 5, with 5 being the highest quality. Plants were no longer considered marketable when the quality rating was lower than a rating of 3 points. The ratings were defined as such:
- 5 points — plant is healthy with no visible decline symptoms
- 4 points — less than 50 percent flower abscission, visible change in flower color or less than 10 percent chlorotic lower leaves
- 3 points — 100 percent flower abscission, less than 50 percent chlorotic lower leaves or less than 10 percent senesced lower leaves
- 2 points — more than 50 percent senesced lower leaves, 100 percent flower abscission or less than 10 percent dead stems
- 1 point — more than 10 per-cent dead stems, 100 percent flowers abscised or 100 percent lower leaves senesced
- 0 points — total plant senescence
Results of the Evaluation
Postharvest decline symptoms in 21 cultivars of vegetative annuals simulated shipping and during shelf life were apparent when removed from shipping or within 1-3 weeks, a reasonable time that garden plants would be held in a commercial outlet. During that simulation, cultivars showed postharvest symptoms of low light intensity, reduced fertilization, high temperature and ethylene gas, as they would in a true retail environment. Lower leaf chlorosis was the most common postharvest decline symptom. Lower leaf chlorosis in shipping boxes and retail environments has been associated with decreased carbohydrates as a result of decreased photosynthesis or a buildup of ethylene gas. The cessation of fertilization and movement of mobile nutrients such as nitrogen to new tissue by the plant could also have contributed to lower leaf chlorosis. Low light and ethylene would play a role in internode elongation, and ethylene would also contribute to flower and bud abortion.
Each species in this study had one or two postharvest decline symptoms common to all cultivars of that species. However, cultivars within species also varied in their postharvest decline symptoms and longevity.
There were few decreases in flower number and quality immediately after shipping, and more decline symptoms occurred as time lapsed in the postharvest environment. Flower abscission directly after shipping occurred on diascia 'Sun Chimes Coral' and nemesia 'Aromatica White'. Both diascia and nemesia are members of Scrophulariaceae. Plants in that family, such as snapdragon and spike speedwell, are ethylene sensitive and abscise flowers in response to ethylene exposure.
During the postharvest evaluation, bracteantha 'Dreamtime Copper', calibrachoa 'Superbells Trailing Blue', nemesia 'Aromatica White' and sutera 'Candy Floss Blue' were the only cultivars to abscise all flowers by the end of the first week.
By two weeks, four more of the 21 cultivars had abscised all flowers, including diascia 'Sun Chimes Coral', the two lantana cultivars and nemesia 'Vanilla Sachet'. Eight more cultivars abscised all flowers by the end of three weeks, and five cultivars still had flowers at termination of the experiment. Of these five, four were bracteantha cultivars including 'Florabella White', 'Florabella Gold', 'Dreamtime Cream' and 'Sundaze Golden Yellow', and petunia 'Cascadias Pink'.
After one week, 13 cultivars had decreased quality as a result of increased shipping duration of one or two days versus zero days, but none were below a marketable quality (less than 3 points). After two weeks postharvest, 12 of the 21 cultivars that were shipped one or two days did not have a high enough quality rating to be considered marketable. These results indicate that plants produced with optimum production practices then held inside a retail garden center need to be sold within the first week of shelf life for the consumer to receive a high-quality plant.
After three weeks, at least one shipping duration treatment of four cultivars was still judged as marketable, including bracteantha 'Florabella Gold', lantana 'Lucky Lemon Cream' and 'Lucky Peach Sunrise', and sutera 'Bridal Showers' — though three of these cultivars were without flowers, and whether consumers would have deemed them acceptable is debatable.
Argyranthemum 'Comet White' retained flowers one week or more than 'Sunlight', although 'Sunlight' was of marketable quality a week longer as a result of less leaf chlorosis. Bracteantha 'Florabella White', 'Florabella Gold' and 'Dreamtime Cream' opened flowers during shelf life regardless of shipping duration. 'Florabella Gold' was still marketable after three weeks, and 'Dreamtime Copper', 'Dreamtime Cream' and 'Florabella White' were marketable after two weeks. 'Sundaze Bronze' and 'Sundaze Golden Yellow' were no longer marketable after one week. Calibrachoa 'Starlette Trailing Purple' retained 23 flowers and marketable quality for two weeks, a week longer than the other calibrachoa cultivars. Lantana 'Lucky Peach Sunrise', nemesia 'Vanilla Sachet', petunia 'Cascadias Pink' and sutera 'Bridal Showers' retained flowers or were marketable quality longer than the other cultivar of their species.