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...
University of Florida Online Greenhouse Training Courses

April 25, 2016

University of Florida Offering Online Training Courses For Greenhouse Growers

There will be five courses offered, with the first starting on May 30. Courses are available in both English and Spanish and range from beginner level to advanced education.

Read More
Sanitation programs are essential to preventing and removing food safety concerns.

April 7, 2016

USDA Launches GroupGAP Program For Fruit And Vegetable Growers

The new certification program is designed to help small and mid-size growers, including greenhouse vegetable producers, comply with new food safety regulations.

Read More
Young Plants Farm North Carolina

March 15, 2016

Young’s Plant Farm Obtains MPS-A Qualification

MPS, an organization that develops and manages certification for companies in the horticulture industry, has awarded MPS-A certification to Young’s Plant Farm in North Carolina and Alabama.

Read More
Latest Stories
University of Florida Online Greenhouse Training Courses

April 25, 2016

University of Florida Offering Online Training Courses …

There will be five courses offered, with the first starting on May 30. Courses are available in both English and Spanish and range from beginner level to advanced education.

Read More
Sanitation programs are essential to preventing and removing food safety concerns.

April 7, 2016

USDA Launches GroupGAP Program For Fruit And Vegetable …

The new certification program is designed to help small and mid-size growers, including greenhouse vegetable producers, comply with new food safety regulations.

Read More
Young Plants Farm North Carolina

March 15, 2016

Young’s Plant Farm Obtains MPS-A Qualification

MPS, an organization that develops and manages certification for companies in the horticulture industry, has awarded MPS-A certification to Young’s Plant Farm in North Carolina and Alabama.

Read More
Charlie Hall Feature Image

March 14, 2016

Dr. Charlie Hall Will Offer Keynote Address At Farwest …

The Texas A&M economist will discuss factors affecting short- and long-term demand driving the future of the green industry.

Read More
Seed Your Future Logo

March 8, 2016

Longwood Gardens And American Society For Horticultural…

Under the direction of co-chairs Paul B. Redman of Longwood Gardens and Anna Ball of Ball Horticultural Company, the “Seed Your Future” initiative is designed to combat declining awareness of horticulture while promoting it as a viable career choice.

Read More
Florida Green Industry

March 4, 2016

University Of Florida Study Shows Green Industry Genera…

According to the study, the rise of large retail chain stores with garden departments has made plants and other horticultural products more readily available to consumers than ever before.

Read More
Great Lakes Growers Expansion

February 22, 2016

Great Lakes Growers Expands Its Production Capacity For…

The Burton, OH-based grower has added 25,000 square feet to its operation, helping it to keep up with rising consumer demand.

Read More
National Garden Bureau Logo feature image

February 16, 2016

New Officers And Directors At National Garden Bureau an…

During the ASTA Flower & Vegetable Seed Conference, National Garden Bureau and All-America Selections elected new officers and directors.

Read More
Katherine Wolper

January 24, 2016

Ludvig Svensson Hires Katherine Wolper As West Coast Sa…

Wolper says she looks forward to listening to growers and understanding the concerns, obstacles, and opportunities they face.

Read More

January 20, 2016

Tips For Overcoming Challenges In Family Business From …

Our industry is run by a collection of family businesses, and every one, no matter how big or small, has its share of management issues. But there are several differences between one that is run successfully as a business and one that allows family politics to distract from the organization’s goals. In this year’s State Of The Industry Survey, we noted that labor recruitment and succession are two areas where growers struggle. In talking with the owners of Costa Farms for this month’s cover story, I thought some of the values they have incorporated into the operation’s management structure really stood out as practices that other family businesses could use. The participatory management approach to business and team building is one that Tony Costa, the second-generation owner of Costa Farms, instilled in his children, Maria Costa-Smith and Jose Costa, and son-in-law, Joche Smith, the current owners of Costa Farms. In […]

Read More
I-9 Form

January 13, 2016

Proposed Changes To I-9 Form Important For Greenhouse G…

AmericanHort’s Government Relations and Grassroots Representative Davi Bowen says growers need to become familiar with the new form and should be prepared to make comments if necessary.

Read More

January 13, 2016

Wenke Greenhouses Buys Zylstra Greenhouses

Two Kalamazoo, MI-based greenhouses have merged after Wenke Greenhouses closed on Zylstra Greenhouses at the end of November. The additional property and facilities will allow Wenke Greenhouses to expand its young plant business, among other areas.

Read More

January 13, 2016

Costa Farms Wins With Its Emphasis On Team, Solutions, …

Based in Miami, FL, Costa Farms has gone global by focusing on strategy, systems, and vertical integration. See how the operation continues to expand through its emphasis on team, solutions, and growth.

Read More

January 11, 2016

New Transportation Funding Bill Is Good News For Floric…

According to AmericanHort, perhaps the biggest benefit of the new bill is what it doesn’t include: a proposed amendment that would have prohibited the use of federal funds for vegetative enhancements.

Read More

December 29, 2015

The Home Depot Says No To Neonics

The Home Depot plans to phase out neonicotinoids by 2018, according to a recent statement on the company’s website. The large home improvement retailer stated that its live goods suppliers have reduced the number of plants that they treat with neonicotinoids, and now more than 80% of all flowering plants sold at The Home Depot are not treated with neonicotinoids. The retailer said it will continue this decrease unless: Treatment is required by state or federal regulation, or Undisputed science proves that the use of neonicotinoids on live goods does not have a lethal or sub-lethal effect on pollinators Aside from these exceptions, the retailer has implemented a complete phase-out of neonicotinoid use on live goods by the end of 2018. Meanwhile, The Home Depot has required all of its live goods suppliers to label plants that have been treated with neonicotinoids. “The Home Depot is deeply engaged in understanding the […]

Read More
Gardeners of all ages enjoyed the annual plant sale at McCorkle Nurseries

December 22, 2015

Allan Armitage Explains Why People Will Always Want To …

We may believe that an appreciation for gardening and plants is rapidly draining away, but there is reason to hope.

Read More
Canadian Greenhouse Conference 2015

December 21, 2015

Presentations From Canadian Greenhouse Conference Avail…

Many of the talks that took place at this year’s Canadian Greenhouse Conference in Ontario focused on improving production efficiencies in the greenhouse.

Read More
Sanitation programs are essential to preventing and removing food safety concerns.

December 7, 2015

How The Finalized Produce Safety Rule Will Affect Green…

While the new rule from FDA has many exemptions that will likely apply to greenhouse growers, the reality is that buyers may still require strict adherence to food safety standards.

Read More
[gravityform id="35" title="false" description="false"]