Cold Water vs. Warm Water

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There still is not  much clear about the impact of the water temperature on the longevity of flowers.  Some florists vow on cold water, others on lukewarm or even warm water. In general: the colder, the better.

Florists differ in their opinion about the “right” water temperature for their cut flowers. Many prefer lukewarm or even warm water to cold. However, a positive effect of warm water has not been  endorsed by any (scientific) research. On the contrary, there are many arguments which are in favor of the use of cold water with almost all cut flowers. As a maximum temperature ranks 10° C.

 

Bacterial growth

Micro organisms as bacteria and fungus grow faster at a high temperature than at a low temperature. At  every temperature rise of 10°C the growth speed is on average three times higher.  So at a start value of 100,000 bacteria per ml/solution (a very realistic number when flowers are put fresh on “clean water”) this number grew in three hours time at 30°C to 2.7 million (see graphic). This is far above the critical limit of 1 million which in general is considered to be the maximum number of bacteria per milliliter.

 

This script only applies when no preservative is added  to the water. But also when using such a product it is a “pity” that the bacterial killing capacity of the product is so heavily burdened during the first hours. This might be at the expense of the activity of the product, after a couple of days. In addition some preservatives do not withstand high temperatures (> 40°C) and become inactive. Higher temperatures and the bacterial growth involved may also cause stem discoloration of flowers with soft stems, such as Gerbera and Chrysanthemum.

Blockage of the flower stems

After the cut flowers are cut off air is sucked in the vessels by the under-pressure in the vascular bundles – this air blocks the water supply. Placing flowers on cold water prevents this blocking in many cases, as in cold water more air can be solved than in warm water.

Acidification of the solution is helpful for a good water uptake. That is why most preservatives reduce the pH value of the water.

Ambient temperature

As the water temperature adopts the  surrounding temperature after some time, one cannot see one thing apart from the other.  The ambient temperature has a significant impact on the evaporation of flowers (through the leaf): the higher the temperature, the higher the evaporation. At an ambient temperature of 2-4°C the evaporation is about one fifth of the evaporation at a temperature of 20°C. The ambient temperature therefore may not exceed 20°C.

Through a higher ambient temperature the loss of water in the flower is so high, that water shortage occurs in the stem causing the flowers and leaves to drop. This is a well-known problem: especially for Bouvardia and Chrysanthemum. At the same time flowers age quicker at higher temperatures and develop faster bacteria and fungus (botrytis). Finally, at a higher ambient temperature flowers are more sensitive for the aging hormone ethylene. This subject will be discussed in a following article.

 

Tips

  • Place flowers in cold water with a well dosed preservative. Water of 10°C at a maximum is recommended. The ambient temperature must not exceed 20°C.
  • Place flowers, especially after dry transport, one or two hours in the cold store to enable them to hydrate well before they are placed in the (cool) shop. It is evident that Anthurium, orchids and other tropical flowers should not be placed in the cold store.

 


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