Cold-Chain Management

Cold-Chain Management

Temperature management is the predominant factor that impacts the post-harvest performance of horticultural crops. Over the past several years, we have been working with cutting suppliers to improve the reliability of delivering unrooted cuttings that perform well in propagation. Inevitably, all roads lead back to temperature management.

Cutting performance relies on strong cold-chain management. The strength of a chain depends on each of the individual links from the time of harvesting the cutting until the cutting is stuck on a propagation bench. This article will discuss why temperature management is so important and will provide guidelines for growers for handling boxes of unrooted cuttings. 

Post-Harvest Physiology 101

Temperature is so critically important because it directly affects physiological processes such as respiration and ethylene production. Let’s take a moment to review some basic post-harvest physiology principles.

Respiration is the process by which carbohydrates (sugars and starches) are broken down into carbon dioxide. During this process, energy is produced. This energy is used to sustain the basic functions and structure of the plant. Respiration consumes oxygen and produces carbon dioxide, so the concentration of these gases will change in the environment surrounding plants that are packaged in the post-harvest environment. Specifically, oxygen can drop from the normal 21 percent of the atmosphere down to as low as 0 to 1 percent. Packages normally have to be tightly sealed to create very low oxygen conditions, but if this happens, then anaerobic conditions are created and this will result in very smelly, rotten plant tissues.

Ambient carbon dioxide is ~0.035 percent, but those levels will increase in the post-harvest environment to as high as 20 percent. Plants can be sensitive to 5 to 10 percent carbon dioxide, which will cause the tissues to break down and become water-soaked.

The rate of respiration in plant tissues increases exponentially as temperature increases. In other words, the respiration rate doubles with every 18ËšF increase in temperature. Thus, if the respiration rate equals one at 40ËšF, then it equals two at 58ËšF. It then doubles again to four as the temperature increases to 76ËšF. Thus, the respiration rate is four times higher at 76ËšF compared to 40ËšF.

Ethylene production by plants is also a function of temperature. The wounding process that occurs when a cutting is removed from the stock plant creates a chain reaction of plant biochemistry that results in ethylene gas being produced by the plant tissues. Ethylene is a signal to the plant that a stress has occurred. If the plants are kept at their optimal post-harvest temperature, very little ethylene is produced; however, after a couple of days in a warm box, one can measure as much as 1 ppm ethylene, which can cause leaf chlorosis and/or rapid leaf abscission. 

Poor temperature management can cause several different problems. In tightly sealed packages, carbon dioxide toxicity or anaerobic conditions (low oxygen) can cause the collapse of plant tissues, although this is quite rare. More commonly, ethylene-sensitive species will display leaf yellowing or leaf abscission. If the exposure to ethylene is relatively high, these symptoms can be observed while the cuttings are being stuck; however, more commonly the symptoms are not expressed until the cuttings have been on the propagation bench for one to four days.

The effects that high respiration rates in the post-harvest environments have on propagation performance are less obvious. To understand this, we must first remember that when a cutting is harvested and placed in a box, its ability to produce more food (carbohydrates) is zero. Thus, the cutting is now having to live entirely off of its carbohydrate reserves. During post-harvest shipping, these food reserves are continually in decline. The warmer the environment, the faster they are in decline.

After two to three days of shipping, the sugar concentrations in the leaves may be negligible. When the cutting is stuck in propagation, the leaves begin to do photosynthesis once again and then start to replenish the depleted carbohydrate levels. This must occur before those leaves can start to supply the base of the stem with the energy need to begin root formation. As a result, the more depleted the cutting carbohydrate levels at sticking, the longer it takes for the rooting process to begin. The bottom line is that a cutting that has experienced cooler temperatures during shipping will begin the rooting process sooner and with greater uniformity. 

Cutting Suppliers Focus On Reliability

Suppliers are currently employing many different and creative strategies for improving temperature management in transit. Oftentimes, the key factor is the proper oversight of package handlers at the airlines and freight carriers. While the proper procedures are put into place at the beginning of each shipping season, it is critical to make sure that the procedures are being properly implemented. Suppliers are sending more dataloggers in boxes than ever before. These loggers provide vital feedback at identifying potential weaknesses in the cold chain.

The ideal amount of ice and insulation in the packaging used for shipping cuttings will vary with the ambient weather conditions. Therefore, cutting suppliers are adapting their boxes with the season and sometimes even week-to-week in order to hit the target temperatures as accurately as is possible. 

Handling Shipments Of Unrooted Cuttings

How the recipient of the boxes handle the product is just as important as all the other links in the cold chain. So what are the best management practices for handling boxes of cuttings?

- Stick cuttings as quickly as possible. This exposes the plants to sunlight and begins the recovery process, while it also removes the plant from the package and reduces exposure to ethylene. The reality is rapidly sticking the cuttings is not always practical, especially when freight deliveries come in the afternoon.

- Understand how sensitive the species is to shipping stress. Species that are difficult-to-ship should be unboxed and stuck ASAP, no questions asked. This list includes: lantana, portulaca, heliotrope, ‘Diamond Frost’ euphorbia and Margarita sweet potato as well as others. Poinsettia and geranium should also be included in the list of moderately sensitive species. It is important to remember that there is a considerable amount of variability amongst cultivars, so the urgency will vary with cultivar. In some cases you may consider sticking the sensitive cultivars first, then stick the remainder of the order the following day.

- Check the temperature of the cuttings upon arrival. Open a few boxes and measure the cutting temperatures with an infrared temperature gun. If the temperatures are below 60ËšF, then the boxes can be placed directly into a 50ËšF cooler. If the temperatures are above 60ËšF, then placing whole boxes into a cooler will not drop the temperatures to desirable levels rapidly enough. Warm boxes need to be opened up and the cuttings should be placed on racks in a cooler. The important thing to note is that a full box of cuttings does not cool down quickly. We have placed warm boxes in coolers for 24 hours and they still have not dropped down to the actual cooler temperature.

- Has the delivery been delayed? If yes, then getting the boxes opened and the cuttings stuck is all the more important. Again, we are simply trying to minimize the time in the box and the exposure to temperatures above 60ËšF. Also, delayed delivery often means the boxes have likely been in the back of a freight company truck that lacks temperature control for a longer period of time. Thus, exposure to non-optimal temperatures is more likely and the importance of handling the cuttings quickly has increased.

- Is it better to place trays of cuttings onto a prop bench even if they won’t get stuck today or should those cuttings go into a cooler overnight? If it is summertime and the greenhouse is quite hot in the afternoon, then placing the cuttings in the cooler overnight and sticking them the next morning is preferable. This is often the case with poinsettias. If it is wintertime and the greenhouse can be relatively cool and the bottom heat is shut off, then the cuttings can be placed on the mist benches, exposed to a few hours of sunlight and then stuck the following morning. This is often the case with geraniums.

- Is dehydration a problem in the cooler? Possibly yes. While transpiration and evaporation are lower at cool temperatures, some coolers are quite dry and have a lot of air movement. These conditions can desiccate cuttings held overnight. In dry situations, additional plastic film or moistened paper may need to be placed over the racks of cuttings to keep the humidity levels up. Water can also be applied to the cooler floor to increase humidity levels.

- Do the cuttings need to be removed from the plastic bags? Most suppliers use bags that have enough holes to allow ethylene to diffuse out of the bags. Simply getting the bags out of the box is helpful.

- What temperature should the cooler be? If just one temperature is possible, then 50ËšF works for the majority of species. Some species, like geranium, prefer 40ËšF, but this will cause chilling injury on many spring species, so 50ËšF is good compromise. There are also some tropicals that require 55ËšF, so in these cases we have to compromise with 55ËšF.

- What should the light levels be in prop? During the first week or two in propagation, we prefer a maximum of 1000 footcandles or 4 moles/day, if you have a sensor that accumulates light levels. Lower levels cause cuttings to recover more slowly from the low carbohydrate levels created during the post-harvest environment.

The bottom line is that every hour in a warm box is one hour too many. All your effort should focus on keeping the boxes cool and reducing the amount of time the cuttings spend inside a box. The sooner the cuttings get placed into the light on a prop bench, the sooner they begin to recover and refill their supply of carbohydrates. Paying attention to these small details will improve your success in propagation.

Leave a Reply

More From Finance/Operations...

April 17, 2015

Sakata Seed Uses California Spring Trials Display Plants To Give Back

Sakata Seed America is putting its post-CAST (California Spring Trials) plants and flowers to good use to support events in local California communities of Salinas and Morgan Hill. The plants, along with donations through Sakata's Charitable Giving Program, will support three fun-filled community events that promote healthy lifestyles and support the agricultural industry.

Read More
Hakonochloa macra Aureola v

April 17, 2015

Ornamental Grasses — A Few Thoughts

Grasses have been embraced by growers, landscape architects and retailers, and are an important component in wholesale and resale sales. Allan Armitage shares some popular grasses, one to avoid and a few to use with caution.

Read More
PW_CAST15

April 17, 2015

Allan Armitage’s Favorite Plants From Proven Winners, Syngenta And Danziger

Between visiting California Spring Trial giants like Proven Winners, Syngenta and Danziger, Allan Armitage saw a lot of great plants in one day. Despite the size of the challenge, Dr. Armitage finds a few favorites he thinks you should try.

Read More
Latest Stories
Syngenta logo

April 15, 2015

Syngenta Names Chris Freeman Senior Key Account Manager…

Chris Freeman is the new senior key account manager for Syngenta Flowers, Home & Garden's Commercial Sales business in the Americas, effective March 2015. Freeman, who joined Syngenta in 2006, carries more than 25 years of experience in the agriculture and floriculture business.

Read More
Lake Buchanan_LCRA

April 10, 2015

USDA Designates Areas Of West And Southwest As Drought …

The ongoing drought has resulted in disaster area designations in counties across nine Western and Southwestern states, including Texas, where some reservoirs are at or near historically low levels.

Read More

April 9, 2015

Altman Plants’ Online Cactus Shop Shows Strong Sa…

Altman Plants recently opened its new Cactus Shop, an online retail store that sells a variety of cactus and succulents. The store is a take-off of Altman’s original wholesale business, as the company started as a mail order catalog.

Read More
Dummen

April 8, 2015

Dümmen Group Welcomes Jim Devereux And Andrew Konicki T…

Dümmen group recently announced the addition of Jim Devereux and Andrew Konicki to its team. They are the newest members of the Key Account and Broker Support team for Dümmen, and will be responsible for building, developing and maintaining current broker and grower customer relationships.

Read More
Gov._Jerry_Brown_California

April 8, 2015

California Institutes First Ever Statewide Mandatory Wa…

California Gov. Jerry Brown announced April 1 that, for the first time in state history, action will be taken to implement mandatory water restrictions, with the ultimate goal of reducing water usage by 25 percent. As Californians are pushed to conserve more, growers will need to think about how demand for products will be affected.

Read More
DNA-logo

March 31, 2015

DNA Green Group Will Acquire Rijnplant

DNA Green Group and Riknplant have finalized DNA Green Group's acquisition of Rijnplant, meaning that the breeding and propagation activities in pot and cut anthurium, bougainvillea and heliconia will transfer to DNA Green Group.

Read More
AFE scholarship_Ryan Dickson

March 25, 2015

AFE Educational Grant And Scholarship Application Deadl…

Apply now for American Floral Endowment (AFE) scholarships or educational grants. Applications can be found online. For educational grants for 2015-2016, applications must be submitted no later than June 1. Scholarship applications are due May 1. AFE will award $40,000 in scholarships for 2015.

Read More

March 23, 2015

UF/IFAS Appoints Joseph Albano As Director Of Mid-Flori…

The University of Florida's Institute of Food and Agricultural Sciences (UF/IFAS) has a new directors for its Mid-Florida Research and Education Center (REC) on Apopka, Fla. The role has been filled by Joseph Albano, a research horticulturist from the U.S. Department of Agriculture with more than 25 years of experience.

Read More

March 17, 2015

Pike Nurseries Implements Employee Stock Ownership Plan

Independent garden retailer Pike Nurseries has announced it will become an employee-owned company. Pike Nurseries management has combined with its sister corporation in California, Armstrong Garden Centers, to operate under an established Employee Stock Ownership Plan (ESOP).

Read More
GrowIt! App Wins Gold At Design100 2014 US Mobile & App Design Awards

March 10, 2015

GrowIt! Mobile App Now Available For Android

The mobile app GrowIt! Garden Socially can now be used by gardeners with Android-based smartphones. Now available on the Google Play Market, GrowIt! helps users find plants to fit their lifestyle and connect them with other local gardeners.

Read More

March 4, 2015

Second Annual GreenhouseConnect Will Bring Growers and …

Following a successful inaugural event in Tampa last fall, Greenhouse Grower has announced the dates of its second annual GreenhouseConnect: October 26-29, 2015. Representatives of an expected two dozen leading greenhouse operations from across the U.S. will join senior-level suppliers at Rancho Bernardo Inn in San Diego for several days of one-on-one strategic meetings, a growers-only roundtable, informational sessions and a variety of networking events.

Read More

March 4, 2015

Maryland Green Industry Associations Unite

The Maryland Nursery and Landscape Association recently announced that it is expanding its reach to include the greenhouse industry, meaning it has become The Maryland Nursery, Landscape and Greenhouse Association (MNLGA). The change comes as a result of the planned dissolution of the former Maryland Greenhouse Growers Association and the invitation for those members to join the existing and renamed association.

Read More
IPPS Sharing Plant Production Knowledge Globally Logo

February 25, 2015

International Plant Propagators Western Region Sets Ann…

The annual meet for the International Plant Propagators' Society (IPPS) Western Region has been set for this September. It will take place September 23 to 26 in Modesto, Calif., and will include learning sessions, tours to local nurseries, a research poster display and poster presentations, various networking opportunities and an awards banquet to close the event.

Read More
myers industries Lawn and Garden Logo

February 24, 2015

Myers Industries, Inc. Lawn And Garden Business Sold, N…

The management of Myers Lawn and Garden Group, along with Wingate Partners V, L.P. have recently acquired the Myers Industries, Inc. Lawn and Garden business. The new company is named The HC Companies, and will continue as a North American leading provider of horticulture containers supplying the greenhouse, nursery and retail markets.

Read More
american-hort-logo

February 17, 2015

AmericanHort Announces New Board Members

AmericanHort recently announced the election of new officers and members to the board of directors. Each will assume their positions on the board during Cultivate’15, July 11 to 14 in Columbus, Ohio.

Read More
All American Selections

February 17, 2015

All-America Selections Elects New Officers, Names New J…

While meeting during the Flower and Vegetable Seed Conference in Tampa, Fla., hosted by the American Seed Trade Association, All-America Selections elected new officers for a two-year term. Read on to learn about the new officers, as well as all of the new judges that were added in 2014.

Read More
Greenhouse Grower.com on your desktop, on your phone, on your tablet

February 11, 2015

GreenhouseGrower.com Relaunches With Responsive Design …

Greenhouse Grower magazine, the nation’s leader in profits, production and education for greenhouse growers, announces the launch of its completely redesigned website, GreenhouseGrower.com. The new design is the product of direct user feedback and GreenhouseGrower.com analytics, and includes responsive design for ease of mobile use.

Read More
Andy Higgins

February 3, 2015

MasterTag Names Andy Higgins As Its New President

Former CEO and president of Ecke Ranch, Andy Higgins, joins MasterTag as its new president. He brings more than two decades of industry experience to the position.

Read More