By Dr. Atif Riaz, Asmat Karim and Muhammad Behzad Rafiq
Cut-flower is the flower which is cut along with a portion of stem, to be used in vases and flower arrangements. Among cut flowers, Gladiolus, Lillium, Gerbera, Chrysanthemum, Carnation, Tulip, Orchids, Anthurium, Gypsophila and Bird of Paradise along with Rose on top are the most favorite flower used for this purpose.
For the trade in cut flower industry vase-life or postharvest longevity is the matter of great importance, where morphological units of cut flowers like sepals, petals, androecium, gynoecium, stem and leaves contribute toward their overall appearance. Both flowers and foliage must remain in presentable form without losing its grade and quality. It is estimated that 30% of flowers loss during handling, 10% become unremarkable due to poor post-harvest conditions and lead to total 50% losses including poor transportation. All cut-flower have varying lasting qualities due to their genetic and physiological structure. This different is due to osmotic concentration and carbohydrates stored in petals. So selection of a good genetic make-up cultivar with resistance to disease and insects and enhanced postharvest life is mandatory. The key to the longest post-harvest life of cut flowers is availability of sufficient sugars/carbohydrates and water which can be retained or even maximized through the maintenance of proper conditions at different stages i.e. pre-harvest, during harvest, and post-harvest. Premium consideration in each case is to minimize stress and maximise vase-life.
Pre-harvest growing conditions including quality of soil/media, fertilization, light, temperature and water, effect flower size, condition, maturity, shape, color and add in post-harvest longevity as well. It is ideal if plants are well watered throughout the growing period and turgid prior to cutting. Since the flowers will have more carbohydrates (sugars and other reserves), it will help them to last longer after harvesting. If flowers are exposed to excessive high temperature beyond the optimize level during cultivation it will also decrease the shelf life as net carbohydrates utilization will be increased. A range between 18-22ᴼC can enhances the vase life of cut flowers. Ideally ttemperature must be cooler prior to harvest. An optimal fertilization program should also be maintained. An excessive supply of N usually decreases vase life because of increased carbohydrate metabolism. While its deficiency can cause paleness of the foliage. Light intensity influences the efficiency of photosynthesis, which also determines the carbohydrates contents of flower.
Flowers are sensitive, perishable and need to be handled with care to increase their post-harvest life where time, stage and mode of harvesting can influence the vase life of cut flowers to a great extent. In general, the best times of the day for harvesting are early in the morning or in the evening. Harvesting particularly in evening is best as the blooms will have the most sugars late in the day. Temperature at the time of harvesting should also be cool or cloudy since there will be less transpiration and attendant water loss. Generally flower cut at more advance stage have shorter vase life than young flowers. Rose, Carnation, Gladiolus, Lily, Iris and Tulip are cut at close bud stage as bud continues to open in sugar solution or water. Whereas, flowers of orchid and gerbera are harvested at fully opened stage. Sharp knives and scratchers need to be used to make a slanting cut on stem as to expose maximum surface and to insurance rapid water absorption. Better to cut in harden portion of stem near the soil. Stem of chrysanthemum should be cut at least 10 cm above the ground level, whereas rose at 2.5 leaflets leaves on the stem. Grading is necessarily to be done immediately after harvesting in which disease and unhealthy blooms are discarded. To remove the field heat pre-cooling should be done at 1-3oC for rose, 4-5oC for gladiolus and 1oC for carnation. Later cut stems can be stored in refrigerator at 4oC retaining 90-95% relative humidity during distribution.
Like pre-harvest conditions number of post-harvest factors affects the vase-life of cut flowers. These include amount of moisture on top. Higher amount of moisture at which the flowers are held, contribute to the longer vase life. Relative humidity should be maintained at 60-80%, which results in less transpiration and subsequent loss of water through the leaves. The quality of the water in which the blooms are held is also quite important and there is no real difference between the use of distilled or tap water. The pH of the water is, however important where acidic water with pH 3.0-5.5, is best as it deters the growth of microorganisms which clog plant stems. In addition, flowers take up acidic water more quickly.
The temperature at which flowers are held is also very important, as an increase in ambient temperature will increase the respiration rate and will result in early aging or senescence. Flowers held at 30ᴼC are likely to respire (and therefore age) up to 45 times faster as compared to the flowers held at 2ᴼC. Flowers should be held at 4ᴼC at which there is less water loss and depletion of sugars occur. However, it is critical, that the flowers must not be frozen. Rapid cooling to remove filed heat and maintenance of the cool chain are thus essential for maintaining quality and satisfactory vase life of cut flowers.
Beside these factors presence or absence of light during storage is generally does not affect cut flowers much, except those where yellowing of foliage is a problem. The leaves of certain cultivars of daisies, chrysanthemum, alstroemeria, and few other flowering plants can turn yellow if stored in darkness at warm temperatures. This problem seems to be induced by low carbohydrate status in the harvested inflorescence, which can be prevented by maintaining the flowers in high light or by treating the harvested flowers with a sugar pulse.
The presence of ethylene gases is bad for many flowers, often causing them to age prematurely. It is therefore important to avoid storing cut flowers with fruits and vegetables that emit ethylene. Ethylene is also produced by damaged tissues and aging flowers, so it is best to keep old flowers away from freshly harvested cut flowers and to ventilate the area of storage. The storage time of cut flowers should be minimized where the maximum period appears to be three to five days. Other possible factors which can cause damage to cut flowers during storage or transportation are bacteria and air bubbles. The use of clean containers and warm acid water after cutting helps to reduce air bubbles and bacteria growth in containers.
Post-harvest life of cut flowers can be extended using different chemicals or preservatives. The purpose of preservatives is to keep the water acidic, to provide sugars, and to counteract the effects of ethylene. For conditioning or hardening hot water treatment can be done at 38-43ᴼC where flower stem are placed in warm water, then in preservative solution, held at room temperature and finally in cold storage for several hours. The quality and vase life of many cut flowers can be improved by pulsing them after harvesting. Pulsing is done by standing the cut flowers in 3-5% sugar solution for 12-24 hours, and often at low temperature. Typical examples are tuberose, where storage life and opening can dramatically be improved by a sugar pulse, and gladiolus, where sugar-pulsed flowers can open further up the spike, grow bigger, and have a longer vase life. Sugar is also an important part of the bud-opening solution used to open bud-cut flowers before distribution, and as part of the vase solution used at the retail and domestic level. AgNO3 treatment for 10 min can protect cut end against blockage of water vessels by microbial growth. GA3, citric acid, STS (silver thiosulfacte), calcium nitrate, aluminum nitrate and sulphate may also be used to keep the flowers fresh till the end of its vase life. Lilies are particularly sensitive to ethylene and treatment with STS can increase its post-harvest longevity.
Further at domestic level remove 1/3 leaves to reduce transpiration along with all leaves below water. It is better to allow clean and fresh air to pass through the room and smoking should be avoided in vicinity. It is also probably best to replace water and preservatives from time to time which can add two or more days to vase life. Spray water with sprayer twice a day and keep removing dried and faded flowers.
About author: Dr. Atif Riaz is working as Assistant Professor at Institute of Horticultural Sciences, University of Agriculture, Faisalabad. He is specialized in the field of Floriculture and Landscape and currently working on development of a sustainable landscape strategy for stress conditions including, drought, salinity, and temperature extremes, by using plant species tolerant to these stresses. Email: email@example.com