Many farmers grow cut flowers for export in Kenya. Proper harvesting and care of flowers after harvest are important to maximize the vase life and ensure a high quality product.

Maximizing the vase life of cut flowers is dependent on pre-harvest procedures too. Long before harvest, variety selection should be considered for postharvest longevity to provide the best possible varieties. The weather conditions and plant environment also affects the postharvest longevity.

Flower Maturity Stage to Harvest
It is important to know the optimum stage of harvesting for each variety to ensure the quality of flowers after harvest. For maximum vase life of cut flowers, harvest flowers daily at their proper stage of development. Harvesting too early or too late significantly reduces the vase life of the flowers. If harvested after the optimum stage, the developing flowers use the carbohydrates that will be used for the development of smaller flower buds, thus, slowing down the growth of other flowers.

Each variety has a minimum harvest maturity stage in which flowers can be harvested without affecting their postharvest quality. In some varieties, disorders such as bent neck, improper development of pigmentation, or abnormal opening of the buds can result when flowers are harvested when they are too immature. If flowers are to be stored or shipped long distances, then they are usually harvested at an earlier stage.

Prior to Harvest

• Plants should be healthy and turgid.
• Plastic buckets and cutting tools should be cleaned and sanitized.
• Avoid stacking buckets if the outside is not as clean as the inside.
• Cutting tools should be sharp. Dull cutting tools can result in crushed stems that reduces water uptake.

Many growers also add a biocide to the water. Biocides are chemicals that prevent the growth of bacteria, yeasts fungi and other microorganisms and are commercially available. Microorganisms and the substances that they produce can plug the xylem (water conducting tissue) of the plant, thus blocking the uptake of water. Researchers have shown that there is a strong inverse relationship between the number of microbes in the water and the Iongevity of cut flowers.

Common biocides are calcium or sodium hypochlorite (bleach), aluminium sulphate, and salts of 8-ydroxyquinoline. Regular household bleach is very short-lived (+/- 4 hours) compared to commercially available slow-release chlorine tablets (about 2-3 days)

Organic Flower Post Harvest Care
Biocides and preservatives are generally not approved for certified organic production.

Organic growers are advised to check with their certifying agent. It is important that certified organic flower growers practice excellent sanitation and harvest at the proper stage of development to ensure maximum vase life for flowers.

Harvesting
Flowers should be harvested in the morning (after dew has dried) or evening, not during the heat of the day. Ideally, flowers should be harvested in the morning when temperatures are low and plant water content is high. Make cuts to the plant to obtain long, sturdy stems. Remove the foliage on the stems that will be below the water which will decay and encourage bacterial growth. Some flowers benefit from removal of most or all of their foliage. Also, for some flowers, side shoots on the main stem are often removed at the time of harvest. Stems can be cut on a slant or straight (square). Slant cuts will keep stems from lying flat on the bucket bottom and increase water uptake.

Flowers should be graded and bunched immediately after harvest. This practice reduces handling steps and minimizes mechanical damages that often occur on the flowers and leaves. If grading and bunching cannot be done immediately, then flowers should be placed in clean buckets. Warm, acidic water reduces air bubbles. Avoid over-filling the containers with flowers to prevent bruising and tangling. The depth of the water in the buckets should be deep enough to cover the bottoms of the stems, usually 1-6 inches depending on the size of the stems and buckets.

During harvest, some growers place buckets at the end of the rows where they place flowers as they cut. Flowers should never be placed directly on the ground or laid on dirty surfaces where they can collect dirt and contaminate the stems and buckets. Flowers and foliage stems should always be kept clean. In addition to clean buckets, cutting tools should be regularly disinfected. Some growers place a bucket containing disinfectant solution and clippers at the end of the row to encourage harvesters to easily exchange used tools for clean ones as they finish a row.

It is best to harvest small quantities at time and bring them into a cool area and place them into the prepared buckets. Buckets placed under portable tents or patio umbrellas work well to create shady areas and reduce heat in the field. A shady area lowers the temperature, reduces water loss and respiration rate of the flowers, and therefore increases the postharvest life and quality of the flowers.

After Harvest Care
After harvesting, flowers are then moved to a cool area where stems can be recut and placed in solutions depending on the specific need of the flowers. Once harvested, flowers continue to transpire and will wilt rapidly. Most flowers will fully recover from wilting if recut and placed in a warm, rehydration solution. Stems are recut by removing about an inch of the end of stems under water prior to placing them in their solution. This helps prevent air bubbles in the water conducting tissue. Air bubbles reduce the uptake of solutions. Always treat flowers before they are sleeved to hasten uptake into the stem.

Importance of Cool Temperatures and High Relative Humidity
Proper temperature management is an important factor for maintaining the quality and vase life of cut flowers. As storage temperatures increase, respiration and water loss increases and wilting occurs. It is important to cool harvested flowers to remove field heat.

For convenience only, export flowers should be moved to a cooler as soon as in order to best preserve quality. The best practice is to harvest flowers at their optimum stage and store them at the lowest possible temperature you can provide without causing freezing or chilling injury.

Generally, the lower the temperatures, the longer the flowers last. Most flowers will retain their quality if stored at temperatures near the freezing point. Others, such as those originating from subtropical and tropical regions, develop chilling injury if stored at temperatures below 50F. Symptoms vary depending on plant species and may include darkening or water soaking of the petals and death of flowers Relative Humidity is another factor that affects uptake of solution. High relative humidity reduces transpiration and keeps flowers from drying out.

Water Quality, Hydrating Solutions
Replace the solution often to avoid allowing the solution to become cloudy, which indicates of the presence of high counts of microbes. Dirty water contains bacteria that will prevent uptake of water. Another important factor is the specific ions contained in the water. Water quality that is good for human consumption may not be good for cut flowers.

Supplying Food
Once harvested, cut flowers are typically placed in a low light or dark environment where photosynthesis is at a minimum. Photosynthesis is a biological process forming carbohydrates (from CO, and H2O in the presence of light), and carbohydrates are needed for the cut flowers to continue to develop. Much of the carbohydrates needed come from starch and sugars stored in the stem, leaves, and petals but the levels may not be adequate. In addition to clean, acidified water with a biocide, a continuous supply of food (sugars) is needed by some flowers for maximum postharvest life of the cut flowers. Water and the addition of preservatives to the solution will result in the best performance of many flowers. Numerous brands and mixtures of floral preservatives and flower care products are commercially available and each is formulated for a different purpose.

The basic types of flower care products include:
Hydrating solutions: After harvest, hydrating solutions are used to facilitate water uptake and restore the turgor of wilted flowers. They are used immediately after harvest and are usually used for a short time, for example four hours. Some growers use hydrating solutions in the field to help prevent flowers from wilting and to restore wilted flowers.

Holding solutions:
In addition to a biocide and acidified water, holding solutions also contain a carbohydrate source (sugar) to encourage bud opening and flower longevity. Holding solutions are usually used after the hydrating solution for several hours for up to two days.

Depending on the intended use of the preservative, the concentration of each ingredient may vary. For example, a preservative formulated for hard water will contain more citric acid or other acidifiers than the general purpose formula. Many, but not all cut flowers benefit from a solution containing 1 to 2% of sugars and a dilute biocide.

Vase solutions: (also called flower preservatives) often contain higher concentrations of carbohydrates than holding solutions and are used by the consumer.

Ethylene
Ethylene, an odorless and colorless gas, is a natural plant growth hormone that affects many physiological processes ranging from seed germination to senescence of plants. Flowers generate ethylene as part of the normal aging process. To maximize vase life of flowers, it is important avoid storing flowers with fruits and vegetables.

Certain cut flowers are very sensitive to ethylene and very small amounts (levels as low as twenty parts per billion) can be very harmful. This level of ethylene is common in supermarkets and in the atmosphere of large cities. Responses to exogenous ethylene vary with varieties, and include abscission, abnormal development of the flower buds, failure of the buds to open and death of the flowers.

In addition to cut flowers, some cut herbs that are being used as cut flowers are also sensitive to ethylene. It is thus important that flowers and greens used for cut flowers that are sensitive to ethylene be handled in areas devoid of ethylene contamination. There are some commercial treatment products to prevent the effects of ethylene by susceptible flowers.

Typically, accumulation of ethylene is minimal in well-ventilated areas, making these spaces suitable for the handling of flowers. However, if flowers are handled in a closed environment, then, it is important to minimize contamination.

Maintaining Straight Stems
Flower stems naturally bend away from gravity and this phenomenon is called geotropism. This bending of the stem away from gravity results in curved stems when they are later placed in a vertical position. These flowers should be handled upright whenever possible.

Mechanical Damage
Mechanical damage to the leaves and flowers reduces the aesthetic value of the flowers and bruised petals and leaves are more prone to infection with disease organisms and ethylene production. The quality of cut flowers is best maintained with gentle and minimal handling.

Botrytis
Cut flowers are susceptible to the fungus disease botrytis, which will cause flowers to turn black and decay. Botrytis has ranges of temperature and relative humidity that are necessary for spore germination, infection and disease development.

Spore germination and infection depends on a film of moisture for 8 to 12 hours, relative humidity of 93% or greater, and temperatures between 55-65F with colonization of plant tissues occurring at temperatures up to 70F.

Management: Botrytis can be managed by proper environmental management. To prevent botrytis, avoid harvesting and storing wet flowers. Also, avoid moving flowers directly from cool to warm rooms which results in water droplets forming (condensation) on flowers, leaves and stems. Maintain dry floors in areas where flowers are processed. Do not dump buckets of water or hose down floors. Wet floors will increase relative humidity and increase the risk for botrytis infection.