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Temperature Effects on Post-harvest Performance

Introduction: Small changes in temperature can have dramatic effects on the rate of physiological processes. In general, a process will be two to four times faster if the temperature is increased 15 to 20 degrees Fahrenheit. On the other hand, a process will be two to four times slower if the temperature is decreased 15 to 20 degrees Fahrenheit. For example, consider data in the following tables.

Effect of temperature on flower deterioration rate and end-user life:

Temperature Relative deterioration Relative life
°C °F rate percent
0 32 1.0 100
10 50 3.0 33
20 68 7.5 13

Thus, a carnation held at 50 degrees Fahrenheit, instead of its proper storage temperature of 32 degrees Fahrenheit, will deteriorate at least three times faster.

Transpiration: Most plants contain about 80 to 95 percent water. Water is the medium through which every biological reaction takes place. It also regulates temperature and promotes nutrient uptake through the roots.

Transpiration is the loss of water vapor by plants. Plants would die because of temperature extremes if water were not lost in this cooling process. Also, if water were not lost from flowers, solution could not be pulled up through the stems. Since transpiration takes place mostly through small openings or "stomata" in leaves, some flowers sold without leaves are prone to bent neck problems (i.e. gerbera). In addition, such flowers don't benefit from fresh-flower food solutions because they take up little solution (i.e. anthurium).

Transpiration is needed for proper post-harvest performance, but it must be controlled to prevent wilting. When water loss is greater than water uptake, plants and flowers wilt. High temperatures and high air movement can increase transpiration rates and hasten wilting.

Respiration: Even more dramatic are the effects of temperature on respiration. Respiration is the process whereby food and oxygen is converted to energy, heat, water and carbon dioxide. Every living entity respites or it dies.

As respiration rates increase in plants, food reserves are used up and flower and/or plant life shortened. The following table demonstrates the effect of temperature on respiration rates.

Relative respiration rates (heat production)of carnations and roses at different temperatures *

Temperature Relative rate of respiration
°C °F Carnation Rose
0 32 1.0 1.0
20 68 24.6 28.3

Respiration rates affect flower quality even more than transpiration rates. In this example, the relative rate of respiration-and hence heat production-of carnations and roses gives a realistic picture of what happens to flower quality when the temperature is too high. For example, flowers which should be held in the low 30s often will be held at or near 68 degrees Fahrenheit. Both roses and carnations respire about 25 times faster at 68 degrees than at 32 degrees. You could postulate from these data that every hour at 68 degrees is equivalent to 24 hours at 32 degrees. Hence, if a flower such as a rose can be successfully stored at 32 degrees for 10 days, holding these flowers at 68 degrees for only five hours prior to 32 degree storage could effectively cut the total possible storage time at 32 degrees in half.

Other research shows that carnations stored at 41 degrees Fahrenheit (five degrees centigrade) for 14 days had their subsequent vase life reduced by over 65 percent, compared to carnations stored for 14 days at 32 degrees. Yet, many people in the flower industry are happy with flowers held at 41 degrees Fahrenheit. Most would also be happy if carnations and roses arrived at 41 degrees. Perhaps these perspectives should be reconsidered.

Ethylene: Ethylene and temperature interact to influence flower quality, too. In short, as temperatures increase, it takes less and less ethylene to kill flowers.

Concentration of ethylene and time of exposure resulting in unacceptable carnation flowers at various temperatures*

Temperature
°C °F Ethylene Exposure Time
0 32 4 Days 2.6
5 41 2 Days 0.9
20 68 6 Hours 2.8
30 86 12 Hours 0.37

While the above data is impressive, ethylene levels as low as 0.03 ppm at 68 degrees Fahrenheit can cause flower problems. Thus, it behooves florists to make sure that flowers and plants are held at proper temperatures to reduce ethylene-induced problems.

* Adapted from Maxie, et al, 1973.

Information reprinted from SAF Flower and Plant Care Manual, (Society of American Florists: Alexandria, VA, 1994), pp. 145-146.