Cut flowers and florist plants/greens

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Cut flowers and florist plants/greens

Description / shipment and storage / Risk factors

1.1 Introduction

International trade in flowers and plants is far more extensive than most people imagine. Most people know that The Netherlands play a large role in this trade. In fact, most people think of flowers – especially tulips – when they think of Holland. But tulips are not the only crop grown in Holland. Dutch growers produce an extremely varied selection of floral produce. And variety is to a high degree the foundation of the competitive nature of this sector of the Dutch economy.

Holland has become the world’s largest cut flower and pot plant exporter. But this small country is also the world’s largest consumer of domestic flowers and plants.

How did Holland achieve this prominent position as an exporter? First of all, Dutch agriculturists believe in cooperation. Researchers, training information services, producers and distributors all work together. Agriculture often is held up as an example to other sectors of the nation’s industry.

The degree of cooperation may be stronger in floral trade and production. Especially the cooperative auctions play an important part in floricultural sales. Holland is located near the most important markets, and, via auctions, offers a wide variety of high quality floral products, included imported varieties, all year. The liberal approach of the Dutch toward competition has heightened its impact on the international floral scene. Researchers, producers and exporters do not set out to compete with developments elsewhere in the world but try to use them to their own advantage. Many sectors of Dutch industrial life have been chosen to beat their competitors, rather than join them. This strategy of confrontation is not the style of the floral sector, which has always been characterised by a more liberal attitude. Cooperation is tailored for the advancement of those involved. This cooperation is evident not only in production and research but also in trading. The untrammelled growth of international trade, boosted by the creation of the European Community, has contributed to the rapid development of production and export of flowers and pot plants. The cooperative auctions have seized opportunities presented by these circumstances and a unique situation has come into being. Not only produce of member-producers is auctioned but, in addition, a wide assortment of flowers and pot plants from all parts of the world is siphoned through the system. Especially during the period that unfavourable climate prohibits growing some varieties in Holland. In this way a complete range of floral products is always available from the auctions. This is unique and set floriculture apart from other sectors of the agricultural industry. Export wholesalers are able to supply almost a complete range of products throughout the year, even during the winter. And this is very attractive to customers.

The traditional export market for Holland is neighbouring Germany, as well as other European countries. In recent years there has been healthy growth in trade with distant markets such as the USA, the Middle Eats, and even Japan, Australia and Hong Kong.

The close cooperation that characterises the Dutch floral industry, combined with continual improvement of the sector, justifies the hope that the industry will take an active role in current international developments. The Aalsmeer flower auction occupies a prominent place in the international flower and plant trading.

2.2 Botany

Plant materials from a wide range of taxa are grown and harvested as cut flowers or florist greens; these include ferns and lycopods, gymnosperms and angiosperms. Because of this diversity, these guidelines include a general review of post harvest requirements for cut ornamentals, followed by brief summaries of the requirements of a range of the most common materials used in commercial floriculture. The references cited are usually the most recent report on a particular crop, and therefore provide an entrée to the literature that is the basis for the recommendations.

2.3 Quality characteristics and criteria

Cut ornamentals are complex plant organs, in which loss of quality of stems, leaves, or flower parts may result in rejection in the marketplace. In some ornamentals, loss of quality may result from one of several causes, including wilting or abscission of leaves and/or petals, yellowing of leaves, and geotropic or phototropic bending of scapes and stems. In evaluating factors that affect the life of ornamentals and how to maximize their market life, it is important first to understand the diverse causes of quality loss.

Growth, development and aging. The whole plant and its individual organs are an integral part of the plant’s life cycle. Even when there is no senescence of floral organs or leaves, continued growth can result in quality loss: e.g., in spike-type flowers that bend in response to gravity. Flower senescence. The early death of flowers and greens is a common cause of quality loss and reduced vase-life for many ornamentals. Flowers can be divided into several categories on the basis of their senescence. Some flowers are extremely long-lived, especially in the Asteraceae and Orchidaceae families, while others are short-lived, including many of the bulb crops, like Tulip, Iris, and Narcissus. Wilting. Extended life for cut ornamentals depends absolutely on a continuing and adequate supply of water. Rapid wilting of shoot tips, leaves, and petals results from an obstruction of the water supply through the cut stems. Leaf yellowing and senescence. Yellowing of leaves and other organs (buds, stems) is commonly associated with the end of display life in some flowers; alstroemeria being an important example. Leaf yellowing is a complex process that may be caused by a range of different environmental factors. Shattering. Abscission and loss of leaves, buds, petals, flowers, or even branchlets is a process called ‘shattering’, and it is a common problem in cut flowers and potted plants. Very often, this problem is associated with the presence of ethylene in the air, but other environmental factors may also be involved.

2.4 Factors affecting postharvest quality

Maintaining the freshness of cut flowers and other ornamentals requires an understanding of the factors that lead to their deterioration. Variety. Many commercial cut flowers and cut greens are patented cultivars, characterized by specific attributes such as colour, form, disease resistance, and size. Sometimes, breeders fail to consider other commercially important attributes. For example, some of the modern alstroemeria cultivars have wonderful flowers, but their display life is short because of rapid leaf yellowing under commercial conditions. There is relatively little published information comparing the postharvest life of different ornamental cultivars.

Postharvest factors. What goes on in the greenhouse or field is an important determinant of the quality and life of cut flowers and foliage. Disease free plants that were properly irrigated and fertilized will produce flowers that look better and perform better in the vase. However, the large leaves on roses grown under supplementary light with CO2 fertilization make them more susceptible to postharvest wilting. Food supply. Starch and sugars stored in the stem, leaves and petals provide much of the food needed for cut-flower opening and maintenance. The levels of these carbohydrates are highest when plants are grown in high light with proper cultural management. Carbohydrate levels are, in fact, generally highest in the late afternoon: after a full day of sunlight. However, flowers are preferably harvested in the early morning, because temperatures are lower, plant water content is higher, and a whole day is available for processing the cut flowers. The quality and vase-life of many cut flowers can be improved by pulsing them immediately after harvest with a sugar solution. Pulsing is done by standing the cut flowers in the solution for a short period, usually less than 24 hrs., and often at low temperature. Typical examples include tuberose, where storage-life and opening are dramatically improved; gladiolus, where flowers open further up the spike, are bigger, and have a longer vase-life; and sweet peas, where vase-life was improved. 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. Potted plants are able to provide their own food supply through photosynthesis if they are held in adequate light conditions.
Light. The presence or absence of light during storage is generally not a concern, except in cases where yellowing of foliage is a problem. The leaves of certain cultivars or chrysanthemum, alstroemeria, marguerite daisy and other crops can yellow if stored in darkness at warm temperatures. The blackening of leaves of cut Protea nerifolia flowers can be prevented by maintaining them in high light or by giving them a sugar pulse. This suggests that the problem is induced by low carbohydrate status in the harvested inflorescence. Water supply. Cut flowers, especially those with large leaf areas, lose water and wilt very rapidly. They should be stored above 95% RH to minimize water loss, particularly during long-term storage. Water loss is dramatically reduced at low temperatures, another reason for prompt and efficient cooling of cut flowers and potted plants. Even after flowers have lost considerable water (for example during transportation or storage) they can be fully rehydrated using proper techniques. Cut flowers will absorb solutions without difficulty providing there is no obstruction to water flow in the stems. Air embolism, plugging with bacteria, plant debris or dirt, and poor water quality reduce solution uptake.

1. Air embolism. Air embolisms occur when small bubbles of air (emboli) are drawn into the stem at the time of cutting. These bubbles cannot move far up the stem, so the upward movement of solution to the flower may be restricted. Emboli may be removed in many ways; e.g., recutting the stems under water (removing about 2 cm), ensuring that the solution is acid (PH 3 or 4), placing the stems in a vase solution heated to 40°C (warm, but not hot) or in an ice-cold solution (0°C), placing the stems in deep (>20 cm) water, or treating the flowers with a detergent ‘pulse’.

2. Bacterial plugging. The cut surface of a flower stem releases the contents of the cut cells (i.e. proteins, amino acids, sugars and minerals) into the vase water. These are ideal food for bacteria, yeasts and fungi, which grow rapidly in the anaerobic environment of the vase. Slime produced by the bacteria, and the bacteria themselves, can obstruct the water-conducting system. This problem must be addressed at every step of the postharvest chain by:

  • Using clean water for making postharvest solutions.
  • Cleaning and disinfecting buckets.
  • Using white buckets – dirt is easier to see in a white bucket.
  • Including a biocide in all buckets and vase solutions. Ca(OCl)2, NaOCl (‘Clorox’), A12(SO4)3, and salts of 8-hydroxyquinoline are commonly used bactericides. An acidic solution also inhibits bacterial growth.

3.Hard water. Hard water frequently contains minerals that make the water alkaline (high PH). Water movement in flower stems is drastically reduced when the water is of high PH. This problem can be overcome either by removing minerals from the water (by using a deionizer, still, or reverse osmosis system) or by making the water acid (ca. PH 3,5). Citric acid is commonly used as a safe acidulant.

Water quality. Chemicals commonly found in tap water are toxic to some ornamentals. Sodium (Na), present in high concentrations in soft water, is toxic to carnations and roses and will cause salt burn (burning of the leaf tips and margins) in potted plants. Fluoride (F) is very toxic to gaillardia, gerbera, gladiolus, roses and freesia. Fluoridated drinking water contains enough F (about 1 ppm) to damage these flowers. Growth Tropisms. Certain responses of cut flowers to environmental stimuli (tropisms) can result in quality loss. Most important is geotropism (bending away from gravity) and phototropism (bending towards light). Geotropism often reduces quality in spike-flower crops like gladiolus, snapdragon, lisianthus, and gerbera, ecause the flowers and spike bend upward when stored horizontally. These flowers should be handled upright whenever possible. Mechanical damage. Physical abuse of cut flowers and foliage results in torn petals, damaged leaves, broken stems. Obvious injuries are undesirable for aesthetic reasons, and disease organisms can more easily infect plants through injured areas. Additionally, respiration and ethylene evolution are generally higher in injured tissues, further reducing storage and vase-life.

2.5 Horticultural maturity indices

Minimum harvest maturity for most cut flowers is the stage at which harvested buds can be opened fully and have satisfactory display life after distribution. Many flowers are best cut in the bud stage and opened after storage, transport or distribution. This technique has many advantages, including reduced growing time for single-harvest crops, increased product packing density, simplified temperature management, reduced susceptibility to mechanical damage and reduced desiccation. Many flowers are presently harvested when the buds are starting to open (rose, gladiolus), although others are normally fully open or nearly so (chrysanthemum, carnation). Flowers for local markets are generally harvested much more open than those intended for storage and/or long-distance transport. Cut foliage is harvested when the uppermost leaves are fully expanded to avoid postharvest wilting of the shoot tips.

2.6 Food supply

The high respiration rate and rapid development of lower buds and flowers indicate the need for a substantial carbohydrate supply to the flowers after harvest. Starch and sugar stored in the stems, leaves, and petals provide much of the food needed for cut-flower opening and maintenance. These carbohydrate levels are highest when plants are grown in high light conditions and with proper cultural management. Carbohydrate levels are generally highest in the late afternoon, after a full day of sunlight. However, flowers are preferably harvested in the early morning, because temperatures are low, plant water content is high, and a whole day is available for processing the cut flowers. The quality and vase life of many cut flowers can be improved by pulsing them after harvest with a solution containing sugar. The cut flowers are allowed to stand in solution for a short period, usually less than 24 hours, and often at low temperature.

2.7 Grades, sizes and packaging

The designation of grade standards for cut flowers is one of the most controversial areas in their care and handling. Objective standards such as stem length, which is still the major quality standard for many flowers, may bear little relationship to flower quality, vase-life or usefulness. Weight of the bunch for a given length is a method that has been shown to strongly reflect flower quality. Straightness of stems, stem strength, flower size, vase life, freedom from defects, maturity, uniformity, and foliage quality are among the factors that should also be used in cut flower grading. If used, mechanical grading systems should be carefully designed to ensure efficiency and to avoid damaging the flowers.
Flowers are normally bunched, except for anthuriums, orchids and some other specialty flowers. The number of flowers in the bunch varies according to growing area, market and flower species. Groups of 10, 12, and 25 are common for single-stemmed flowers. Spray-type flowers are bunched by the number of open flowers, by weight or by bunch size. Bunches are held together by string, paper-covered wire or elastic bands and are frequently sleeved soon after harvest to unitize the bunch, protect the flower heads, prevent tangling, and identify the grower or shipper. Materials used for sleeving include paper (waxed or unwaxed), corrugated card (smooth side towards the flowers) and polyethylene (perforated, unperforated and blister). Sleeves can be preformed (although variable bunch size can be a problem), or they can be formed around each bunch using tape, heat-sealing (polyethylene), or staples. There are many shapes of packing containers for cut flowers, but most are long and flat. This design restricts the depth to which the flowers can be packed in the box, and this may reduce physical damage. In addition, flower heads can be placed at both ends of the container for better use of space. With this kind of flower placement, whole layers of newspaper are often used to prevent the layers of flowers from injuring each other. The use of small pieces of newspaper to protect only the flower heads, however, is probably the better practice, since its allows for more efficient cooling of flowers after packing. It is critically important that containers be packed in such a way that transport damage is minimized. Some packers anchor the product by using enough flowers and foliage in the box so that flowers in the package, after banding, are immobilized by the surrounding material. To avoid longitudinal slip, packers in many flower-producing countries use one or more ‘cleats’. These are normally foam- or newspaper-covered wood pieces that are placed over the product, pushed down, and stapled into each side of the box. Padded metal straps, elastic bands, high density polyethylene blocks, and cardboard tubes can also be used as cleats. The heads of the flowers should be placed 6 to 10 cm from the end of the box to allow effective pre-cooling and to eliminate the danger of petal bruising should the contents of the box shift. Gladioli, snapdragons and some other species are often packed in vertical hampers to prevent geotropic curvature that reduces their acceptability. Cubic hampers are used for upright storage of daisies and other flowers. A new packaging system, the ‘Procona’ system, uses plastic bases and a cardboard sleeve to allow transport of flowers upright in water. This system is more expensive than traditional boxes, and less product can be packed in it, but the presence of water, may improve flower quality when they are not transported under proper temperature conditions. Specialty flowers such as anthurium, orchid, ginger and bird-of-paradise are packed in various ways to minimise friction damage during transport. Frequently, flower heads are individually protected by paper or polyethylene sleeves. Cushioning materials such as shredded paper and paper or wood wool may be placed between packed flowers to further reduce damage.

2.8 Pre-cooling conditions

By far the most important part of maintaining the quality of harvested flowers is ensuring that they are cooled as soon as possible after harvest and that optimum temperatures are maintained during distribution. Most flowers should be held at 0°C to 1°C. Chilling-sensitive flowers (anthurium, bird-of-paradise, ginger, tropical orchids) should be held at temperatures above 10°C.

Once packed, cut flowers are difficult to cool. Their high rate of respiration and the high temperatures of most greenhouses and packing areas result in heat build-up in packed flower containers unless measures are taken to ensure temperature reduction. It is therefore necessary to cool the flowers as soon as possible after packing. Individually, flowers cool (and warm) rather rapidly (half-cooling times of a few minutes). However, individual flowers brought out of cool storage into a warmer packing area will warm quickly and water will condense on the flower. The simplest method of ensuring that packed flowers are adequately cooled and dry is to pack them in the cool room. Although this method is not always popular with packers, and may increase labour cost and slow down packing somewhat, it will ensure a cooled, dry product. Forced-air cooling of boxes with end holes or closable flaps is the most common and effective method for pre-cooling cut flowers. Cool air is sucked or blown through the boxes. Care must be taken to pack them so that air can flow through the box and not be blocked by the packing material or flowers. In general, packers use less paper when packing flowers for pre-cooling. If the packages are to remain in a cool environment after pre-cooling, vents may be left open to assist removal of the heat of respiration. Flowers that are to be transported at ambient temperatures can be packed in polyethylene caskets, foam-sprayed boxes or boxes with the vents resealed. Ice that is used after pre-cooling is only effective if placed to intercept heat entering the carton (i.e., it must surround the product), and care must be taken to ensure that the ice does not melt onto flowers or cause chilling damage. Pre-cooling of vertical hampers or Proconas presents a particular challenge, but can be achieved using a ‘tunnel’ forced-air cooling system.

2.9 Chilling sensitivity

Some tropical crops such as anthurium, bird-of-paradise, some orchids, ginger and many foliage plants are injured at temperatures below 10°C. Symptoms of ‘chilling injury’ include darkening of the leaves and petals, water soaking of the petals, and, in severe cases, collapse and drying of leaves and petals. Special care needs to be taken with tropical flowers shipped in a mixed load. The flowers should be packed in plenty of insulating material (an insulated box packed with shredded newsprint, for example). These flowers should not be pre-cooled. If they are to be shipped by refrigerated truck, they should be placed in the middle of the load, away from direct exposure to cooling air.

2.10 Ethylene production and sensitivity

A number of flowers, especially carnations, gypsophila and some rose cultivars, senesce rapidly if exposed to minute concentrations of ethylene gas. A number of flowers (like carnations and sweet peas) produce ethylene as they age and this endogenous ethylene is involved in the death of the flower. Other flowers, such as snapdragon and delphinium, produce little ethylene themselves, but exogenous ethylene causes flower abscission (or shattering). Concentrations of ethylene above 100 ppm in the vicinity of sensitive ornamentals can cause damage and therefore should be avoided. Storage and handling areas should be designed not only to minimise contamination of the atmosphere with ethylene, but should also have adequate ventilation to remove any ethylene contamination that may occur. Finally, refrigerated storage is beneficial in that both ethylene production and sensitivity are reduced greatly when temperatures are low.

2.11 Optimum storage conditions

The vase-life of flowers that are stored even for a few days is closely correlated with their respiration during storage. Rapid cooling and proper refrigeration are thus essential to maintain quality and satisfactory vase-life of cut flowers and foliage. The recommended conditions for commercial storage of most cut flowers are 0°C to 1°C at 95% to 99% RH. In contrast, some tropical crops, such as anthurium, bird-of-paradise, some orchids and ginger, are injured at temperatures below 10°C. Although flowers are commonly held in water for short-term storage, better vase-life after longer storage is achieved by storing the flowers dry. Under these conditions, stable temperatures (to reduce condensation and Botrytis infection), and high RH are essential. Flowers for longer-term storage are typically wrapped in newsprint (to absorb any condensation) and perforated polyethylene (to reduce water loss). Storage-life varies by species, but is typically less than 3 weeks.

2.12 Controlled atmosphere (CA) considerations

There have been relatively few reported benefits of CA storage for cut flowers. Any consideration of the use of CA must follow achievement of proper temperature control and elimination of the effects of Botrytis during storage. Recommended atmospheres vary from pure nitrogen (daffodils) to more conventional atmospheres (carnations).

2.13 Retail outlet display considerations

The simple way to ensure rapid re-hydration of all but the most difficult or desiccated flowers is to re-cut the stems and place them in a clean bucket of water containing a quality flower preservative solution in the cooler. The pH of the preservative solution should be below 5. For badly wilted flowers a re-hydration solution may be helpful, since the sugar in vase preservatives reduces the flow of water in stems. Flowers with woody branches respond particularly well to low pH (3,5 is optimal), and some flowers (sunflowers, astilbe) respond well to a 10 minute ‘pulse’ with a 0,02% detergent solution. Flower coolers should be >5°C; flowers should be placed in the coolers when not on display or being used for preparing arrangements.

2.14 Respiration rates

Cut flowers have extremely high rates of respiration, and respiration increases exponentially with temperature. Different cultivars of the same species may have quite different respiration rates and may respond differently to temperature.

2.15 Physiological disorders

There are relatively few recognized physiological disorders in the postharvest life of cut flowers and foliage. ‘Topple’ of tulips, a collapse of the scape, is a disorder associated with low calcium status of the flowers. Petal blackening in some red roses has been suggested also to be associated with inadequate calcium and perhaps boron nutrition.