A Longer Vase Life with Chlorine Dioxide

Researchers at the University of Florida, Gainesville, evaluated the use of chlorine dioxide as a safe, effective biocide for inclusion in vase solutions to extend the vase life of cut flowers. Antimicrobial compounds are known to reduce the number of bacteria in vase water; however, some are not as effective in the acidified solutions commonly used for hydrating and others are limited in commercial use due to human health concerns. Chlorine dioxide is known to work as a biocide over a broad pH range and is considered safe for use, even at low concentrations on fresh produce.

This test included 10 species: Alstroemeria peruviana, Antirrhinum majus, Delphinium, Dendranthema x grandiflorum, Dianthus caryophyllus, Gerbera jamesonii, Gypsophila paniculata, Lilium asiaticum, Matthiola incana, Rosa hybrid. All stems were grown in Colombia or California and shipped to the lab in Florida according to specific protocol. The alstroemeria, delphinium, dianthus and gypsophila were pretreated with silver thiosulfate for ethylene protection.

Surface-sterilized vases were prepared with a chlorine dioxide solution at concentrations of 0, 2, 5, 10, 20, and 50 µL/L. Additionally, vase solutions were prepared with varying bacteria concentrations and subsequently treated with 10 µL/L chlorine dioxide or none. A pre-treatment experiment was performed on the gerberas prior to shipping. Half the stems were dipped in a 10 µL/L chlorine dioxide solution for one minute. The final experiment compared the efficacy of chlorine dioxide treatments to the other biocide options commonly used, such as 8-HQS, aluminum sulfate, Physan 20™, DICA, and Clorox™. Vase life of each species was subjectively judged according to marketable characteristics and recorded as number of days.

The addition of aqueous chlorine dioxide in concentrations as low as 10 µL/L, or in some cases 2 µL/L, resulted in significantly extended vase life of all the species tested except Delphinium ‘Bellamosum’ and Dendranthema ‘Albatron’. Even in those two species, the number of bacteria in the vase solution was significantly reduced compared to the control, but the control lasted as long as the treatments. Chlorine dioxide concentrations of 50 µL/L resulted in leaf chlorosis and flower abscission in Alstroemeria ‘Senna’, Delphinium ‘Bellamosum’, Dendranthema ‘Albatron’and Lilium ‘Vermeer’.

Pre-treatment of Gerbera stems resulted in a vase life extension of 4 days compared to those that did not receive any pretreatment. The pre-treatment prevented the accumulation of bacteria in the water used to rehydrate the flowers after a 1-day dry shipment from the farm to the lab. Chlorine dioxide and 8-HQS were most effective in extending the vase life of three Gerbera cultivars, compared to the other commercially-accepted biocides tested. Considering the health concerns regarding repeated exposed to 8-HQS, chlorine dioxide looks like a promising vase solution additive for at least these eight cut flower species.

Macnish, A.J., R.T. Leonard, T.A. Nell. 2008. Treatment with chlorine dioxide extends the vase life of selected cut flowers. Postharvest Biology and Technology. 50, pp. 197-207.

Testing Biodegradable Mulching Materials and Snapdragons

Research conducted at the University of Bari in Italy compared two biodegradable mulch materials to the commonly used low density polyethylene (LDPE) film. Snapdragons were grown and evaluated to determine how the different mulches affected the substrate temperature and subsequent plant growth and development.

The field test was carried out in a greenhouse in a soil-less media. The three mulch materials tested were: transparent biodegradable mulching film, transparent LDPE mulching film and transparent spray mulching coating. Unmulched medium served as the control. The biodegradable film (Mater-Bi grade NF, supplied by Novamont Co.) was 30 µm thick, made from a starch-based raw material. The LDPE film was 60 µm thick, supplied by Pati Co. Both films were secured on top of the media. The biodegradable spray (PSS20 Protective Surface System) was sprayed over saturated media using a high pressure airless spray machine. The resulting thickness was approximately 50µm. Three weeks after the mulch was applied, the snapdragons were transplanted in the media. The plants grown in each mulch treatment began to flower 7 days earlier than those snapdragons grown in the unmulched control. The number of flowers produced was the same for all treatments. The harvest period was shortest, at 8 days, for the film mulches and longest for the spray mulch (19 days). The harvest interval for the control plants was 12 days. The mean days to bloom decreased and stem length increased as substrate temperature increased. The LDPE film demonstrated the highest average substrate temperature (25.8C/78.4F), followed closely by the biodegradable film (28.8C/83.8F) and then the biodegradable mulch (23.7C/74.7F). Lab tests to determine the radiometric properties of the mulches determined that the biodegradable materials were more reflective of the solar radiation.

The lifetime of the biodegradable materials was also tested. For the five months of experimentation, neither biodegradable mulch showed visible signs of biodegradation. While the biodegradable film remained unbroken during the growing period, the spray mulch had some cracking within the first month. Despite the cracking, the coating maintained its mulching effect for the entire crop cycle. After the harvest was completed, the biodegradable materials were fragmented and mixed with the growing medium and plant residue. The spray mulch proceeded to degrade within one month while the biodegradable film required nearly 12 months. Several variables, such as humidity, and size and thickness of the fragmented mulch pieces, contribute to the rate of degradation.

Schettini, E., G. Vox, and B. De Lucia. 2007. Effects of the radiometric properties of innovative biodegradable mulching materials on snapdragon cultivation. Scientia Horticulturae. 112, pp. 456-461.

Comparing Organic and Inorganic Fertilization for Growing Statice and Cockscomb

The certified organic farm plots at West Virginia University in Morgantown, West Virginia, were the testing grounds for a nutritional study focusing on the organic production of statice and Celosia. Additionally, the research considered if these two specialty cut flowers would be viable options for farmers in the midst of transitioning from conventional production to organic.

These particular species were selected because statice (Limonium sinuatum) has relatively low nutrient requirements, and Celosia argentea is considered a high nutrient requiring plant. Five rates of a composted dairy manure-leaf litter mix were tested. The compost was applied at rates of 0, 6.2, 12.4, 24.7, 49.4, and 98.8 tons/hectare each year being tilled in to a depth of 10 cm prior to planting. A once-over harvest was performed and characteristics, such as color, stem length and stem fresh weight, were recorded for the marketable stems. The experiment was carried out in 2001 and 2003.

A greenhouse study was also conducted using conventional fertilizers to gain a better understanding of these species’ organic fertilization requirements. The greenhouse experiment tested four rates of nitrogen and six rates of phosphorus.

The nutrient analysis of the compost was approximately 0.5% nitrogen both years. The phosphorus measured 66% in 2003 compared to 24% in 2001; however the harvest data collected over the two growing seasons was averaged for further analysis. The statice demonstrated a linear increase in fresh weigh per plot and number of stems per square meter as the amount of compost increased. The weight per stem increased up to the 49.4 t/ha rate, then decreased at the highest compost rate. The Celosia showed a linear increase in fresh weigh per plot, weight per stem, and stem length as the compost rate increased. The number of stems per square meter increased up to the rate of 65 t/ha (according to the quadratic curve of the analysis), then dropped off. The greenhouse studies resulted in similar results, though direct comparisons cannot be made.

This study produced two basic conclusions: 1) Statice is a better choice for a specialty cut flower (compared to Celosia) for use during conversion from conventional to organic production requiring small amounts of composts to provide adequate plant nutrition and 2) The phosphorus analysis of compost should be given more consideration than the nitrogen amount with regards to nutrient applications since acceptable cut flower production was achieved under low nitrogen circumstances.

Verlinden, S., L. McDonald. 2007. Productivity and quality of statice (Limonium sinuatum cv. Soiree Mix) and cockscomb (Celosia argentea cv. Chief Mix) under organic and inorganic fertilization regiments. Scientia Horticulturae. 114, pp. 199-206.

Megan Bame

Megan Bame is a freelance writer in Salisbury, North Carolina. Contact her at [email protected]