In the previous issue of Landscape SA, an article entitled "Cultivation of Cut Flowers" was featured, extracted from the book Cut Flowers of the World by Johannes Maree and Ben-Erik van Wyk. In this issue and subsequent ones, further extracts from the book, published by Briza, will appear.
The harvesting of cut flowers is in most cases labour intensive and all fo this handling often results in physical damage to the flowers. To minimize damage, growers are continually trying to reduce the number of times a flower is physically touched by a person. Cut flowers are not only harvested on cut flower farms, but also from the wild. In many countries, cut flowers as well as foliage are harvested from their natural habitat. If not properly controlled, this sort of cut flower industry can cause damage to the environment and will not be sustainable. In South Africa and Australia, where wild harvesting is regularly practiced because of the rich floral diversity, regulations are in place to ensure that biodiversity is not lost and that sustainability is maintained. Wild-harvested flowers often have problems such as pests and diseases, as well as a lack of the desired characteristics found in cultivated flowers such as crooked stems, limited colours and a shorter vase life. Research is therefore continually being done on naturalizing, breeding and cultivating potential species harvested form the wild.
Stage of harvest
The opening stage at which flowers are harvested has an influence on their vase life and how well the flowers will continue to open. If the flowers are harvested too early, the carbohydrate reserves (starch and sugar) are too low These carbohydrates are a source of energy or food needed by the flower to live and continue to open. Furthermore, carbohydrates help to maintain turgidity, thus preventing the flower from drooping or wilting too quickly.
If flowers are harvested too late, they would have passed their prime and also have a shorter vase life at the consumer. It is not always easy to determine the exact stage at which a flower must be harvested. Besides the carbohydrate factor, there is also the market demand factor. Different markets or customers what their flowers at different opening stages. Flowers harvested for local consumption are often harvested more open than those harvested for export.
Time of harvest
Flowers should be harvested in the cool of the day, either early morning or late afternoon. Early in the morning flowers are still turgid, i.e full of water and firm. During the heat of the day they lose a lot of water through transpiration. Often more water is lost than can be taken up and thus temporary wilting takes place. Even if these flowers are picked and immediately placed in water the results are not as good and quality is lost. The flowers might stand up again, especially when placed in a cool-room but a lot of unseen damage may already have been done and flowers picked in the heat of the day will never last as long as flowers harvested in the early morning or late afternoon. Many researchers recommend that the best time to harvest flowers is late in the day when the carbohydrate reserves are at their highest, but this may not be practical. However, water reserves are usually best in the early morning so both times are fine for harvesting. The timing and frequency of harvesting per day also depends on the type of flower grown and the size of the operation.
Heat kills flowers. At high temperatures, flowers respire much faster than at lower temperatures. Respiration and transpiration lead to a significant loss of water. This excessive water loss causes severe damage to cell walls, leading to permanent wilting. Temperature is a critical factor in the whole quality chain. For every 10 degree temperature decrease, the speed of the physiological processes in plants is on average reduced by two to three times. Field heat needs to be removed from flowers as soon as possible after harvesting and a cold chain maintained. Each flower type has a minimum temperature at which it can be stored and anything below this could result in cold damage.
A primary factor determining the consumer quality of cut flowers is temperature management during handling and transportation. It is therefore of utmost importance to try to maintain the cold chain as efficiently and as long as possible. Transporting cut flowers in water does not replace the need to transport them at low temperatures. The main emphasis in maintaining the cold chain is to ensure flower quality, freshness and vase life.
Most flowers are best stored at 4-6 degrees C and at 90% relative humidity but this does not mean that they can be stored indefinitely at those temperatures. They still need to be sold as soon as possible. Preferably, flowers should not be held for longer than three to four days in a cool-room; after that, they start to lose quality rapidly. For florists who work with a variety of cut flowers but have only one cool-room, it is best to set the temperature at 4-6 degrees C and the relative humidity at 90%. However tropical flowers still need to be stored at a higher temperature of 13-15 degrees C and a relative humidity of 90%.
Even in storage, transpiration continues and this can lead to unacceptable moisture loss that cannot be effectively replaced, leading to premature wilting and death of the flower. The main cause of transpiration is the vapour pressure deficit (VPD) which is the combined effect of temperature and relative humidity. When the VPD is high, the transpiration rate of flowers is also high. A low transpiration rate, which is ideal, can be obtained by a combination of low temperature and high humidity. Therefore there should be some mechanism for controlling humidity in flower cool-rooms. If the humidity is set too high (over 95%), other problems arise such a condensation on the cool-room ceilings and walls. This causes a lot of damage to flowers as the condensation drips onto the flowers, also creating an ideal environment for the outbreak of diseases such as botrytis.
Sanitation and hygiene
Flower quality and vase life are dramatically affected by the level of sanitation and hygiene. The main areas to focus on are working surfaces, tables, cool-rooms, equipment, tools and vehicles. All of these need to be cleaned daily and regularly sterilized. Washing with soap and water means it may be clean but it is not disinfected. To achieve full hygiene, a disinfectant needs to be used as well.
The proper grading according to market standards and demands is vital. Grading affects the overall quality of flowers. Flowers in a bunch should be uniform in all aspects, i.e in their opening stage, length, colour and grade. Few things irritate a buyer or end consumer more than a poorly graded bunch of flowers, and they often regard this as poor quality or dishonesty on the part of the supplier. Presentation forms a vital part of perceived and real quality of cut flowers.