How to maintain the quality of your plants during shipping and maximize their shelf life
Poor postproduction care and handling can quickly reduce the quality and salability of bedding and pot plant crops. Implementation of vendor-managed inventory systems, including pay-by-scan, where growers are only paid for the products that are sold, has quickly made growers aware of the importance of maintaining crop quality during shipping and retailing.
While some crops are produced and sold to the final consumer at the same site, others make the journey by truck to a retail location that may be states away from the production facilities. Most growers want to do everything they can to insure that when their plants come off the delivery truck they look as good as when they were loaded. After shipping, plant quality may be reduced due to stretching, leaf yellowing, petal shattering, bud drop, flower fading or flower or whole plant wilting. These symptoms can be caused by temperature extremes, low light, inadequate watering and/or exposure to ethylene gas.
Proper care and handling during order assembly and loading goes a long way toward preventing shipping damage. Before shipping, remove all dead or diseased flowers and leaves. These can serve as a source of inoculum for Botrytis and other diseases that may spread throughout the truck.
Dying plant material also produces ethylene. Ethylene is a gas that causes premature wilting of flowers, leaf yellowing and abscission of buds, flowers and leaves. Handle plants with care to avoid mechanical breakage, which can make them more susceptible to disease and ethylene damage.
Avoid shipping problems
Shipping plants in rolling racks is an efficient way to move them from the production area and load them on delivery trucks. Wrapping the racks with plastic can help keep the plants on the racks, but it can also increase ethylene and disease problems. The plastic creates a high moisture microenvironment that is conducive to Botrytis infection and traps ethylene around the plants. The time that plants are wrapped, boxed or sleeved should be minimized to prevent ethylene damage.
Maintaining plant quality during shipping is all about reducing the plant’s exposure to environmental stresses. The primary issue during shipping is temperature. For most spring and summer crops the challenge is keeping the plants cool.
|Plants in the photos: Plants on the right of each photo were treated with 2 parts per million ethylene for three days. Plants on the right were treated with ethylene- free air (0 ppm ethylene). Marigolds are insensitive to ethylene and do not show any damage on flowers or leaves. Ethylene-treated impatiens have dropped all open flowers and buds. The plants also show symptoms of epinasty, which is the downward curvature of the leaves.
Environmental conditions during production have been optimized for maximum photosynthesis. Photosynthesis allows plants to build up food reserves and to grow. Photosynthesis is reduced during shipping primarily due to low light levels. The predominant plant metabolic process during shipping is respiration. Respiration uses up the plant’s food reserves and negatively impacts shelf life. Therefore, the goal during shipping and retailing is to minimize respiration and conserve the plants’ energy reserves so that they will have an adequate shelf life.
Plant respiration rates are higher at higher temperatures, so maintaining lower temperatures during shipping and retailing reduces respiration and translates into increased quality and shelf life. Using refrigerated trucks is the best way to manage temperatures during shipping, but this is not a viable option for most crops. Instead take advantage of cooler morning or evening hours to load and ship plants.
Combating Ethylene damage
Ethylene is a gas produced by plants when they are under stress or when plant parts like leaves or flowers are dying. Plants exposed to high temperature stress produce more ethylene and are more sensitive to external sources of ethylene. Ethylene causes more damage to plants at higher temperatures. This can result in devastating damage during shipping. When ethylene is produced by a plant it not only affects that plant, but the gas accumulates in enclosed areas like delivery truck trailers and can damage an entire plant shipment.
Ethylene gas is best known for causing fruit ripening (or over-ripening) and is the reason that “one rotten apple spoils the bunch.” Flowers are more sensitive to ethylene contamination than leaves.
The most common symptoms of ethylene damage during shipping are petal or bud drop, or flower wilting. Some plant species are very sensitive to ethylene and respond to very low concentrations with extreme symptoms.
One ethylene sensitive plant is impatiens. It is not uncommon for an entire shipment of impatiens to arrive completely flowerless because they have been exposed to ethylene in the delivery truck. Other species like marigolds have low sensitivity or are insensitive to ethylene. Marigolds can be in the same truck as the impatiens and not have any symptoms of ethylene damage.
Table 1 below lists some plant species that are generally considered to be sensitive to ethylene. Ethylene sensitivity also varies between cultivars. A source of information on plants that are sensitive to ethylene is the Chain of Life Network (www.chainoflifenetwork.org/).
In addition to the plants themselves, there are other sources of ethylene that you should be aware of. Gasoline engines and the incomplete combustion of propane can contaminate growing and shipping areas with ethylene. Using electric forklifts and carts when transporting plants in the greenhouse and when loading trucks can eliminate this source of ethylene.
Do not let trucks idol in the shipping area as the engine exhaust can contain ethylene. It is also best to avoid shipping or storing flowering plants with produce, like apples and tomatoes, that synthesize and release a lot of ethylene.
|s-ABA (Contego Pro SL) applications delay drought-induced wilting in New Guinea impatiens and chrysanthemums. Plants on the right of each photo were sprayed with 1,000 (impatiens) or 500 ppm (mums) Contego + 0.05 percent surfactant (CapSil). Control plants on the left were sprayed with surfactant only. Photos were taken at nine days (impatiens) and seven days (mums) after treatment and last irrigation.
If you are shipping plants that are sensitive to ethylene, it can be worth the extra expense to treat these plants with a product that makes the plants insensitive to ethylene. The anti-ethylene product 1-MCP (Ethylbloc or Ethylene Buster) is available in sachets that can be dipped in water and placed in the boxes with the plants. These sachets give off a gas called 1-methylcyclopropene that has a similar chemical structure to ethylene and effectively prevents the plant from responding to the ethylene.
If plants are being shipped in open racks, a truck treatment kit can be used. The 1-methylcyclopropene gas is released throughout the truck to protect the entire shipment. Even if there is ethylene in the environment, treated plants are protected and they will arrive with green leaves and intact flowers.
Orchids are routinely treated with anti-ethylene products. Orchid flowers are very sensitive to ethylene and when sealed in boxes for shipping across the country, these normally very long-lived flowers are often wilted due to ethylene exposure.
Prevent transpiration and wilting
During shipping, high temperatures can cause rapid substrate drying and plant wilting. A common cause of reduced sales is drought-induced wilting. This is especially prevalent in crops like impatiens that use water rapidly or in bedding plants or hanging baskets with relatively small substrate volumes. Potted and bedding plants can be irrigated with a wetting agent just before shipping to increase water retention within the growing substrate.
Anti-transpirants can also be applied to reduce water loss and delay wilting if plants experience water stress during shipping or retailing. Anti-transpirants reduce water loss by physically blocking or causing the plant to close the microscopic pores on their leaves called stomata. Transpiration rates are reduced and wilting is delayed. A good candidate for anti-transpirant application would be crops like chrysanthemums that are not turned over quickly and need a shelf life of a week or more.
Figure 2 illustrates the effectiveness of the anti-transpirant s-abscisic acid (s-ABA) (Contego Pro SL) on drought-stressed New Guinea Impatiens and chrysanthemums. Well-watered plants were sprayed with s-ABA and then water was withheld. Untreated plants were wilted and unmarketable after four days, while treated plants were still considered marketable after nine days (New Guinea impatiens) and seven days (mums) without any irrigation. Under these conditions, s-ABA applications resulted in a three- to five-day extension in the shelf life of plants under drought stress. While this product is very effective on mums and New Guinea impatiens, the effectiveness varies with species and between cultivars, and side effects including leaf shedding and yellowing have been observed. Always test any chemical on a few plants before treating a whole shipment.
Identify shrink rates
Identifying shrink rates at all stages of the marketing chain can help you determine where shrinkage can be reduced. If your postproduction shrink rates are higher than you would like, this is an opportunity to implement some of the practices presented in this article.
Michelle Jones is associate professor and D.C. Kiplinger Chair in Floriculture, Ohio State University, firstname.lastname@example.org. Terri Starman is associate professor, Texas A&M University, email@example.com. Charles Hall is professor and Ellison Chair in International Floriculture, Texas A&M University, firstname.lastname@example.org. Claudio Pasian is associate professor, Ohio State University, email@example.com. George Staby is owner, Perishables Research Organization, firstname.lastname@example.org.