Respiration and Temperature

• Plants grow and bloom by converting sunlight into carbohydrates in leaves and carrying nutrients up from the soil to the growing tips or flowers to create tissue. The process of photosynthesis and conversion of nutrients to tissue is the plant version of respiration. Flowering is the life goal of flowering plants and requires increased respiration. As temperatures warm, plants process sunlight, nutrients and water faster, providing the increased energy needed by flowers. In addition, the process of respiration itself generates heat, speeding up the flowering process. Cooling plants slows down plant respiration.
  
  

Water and Respiration

• Water carries nutrients through plants and hydrates flower tissue.Jupiterimages/Photos.com/Getty Images
  
  Water travels between layers of tissue on leaves and stems as part of the respiration process. Commercial flower growers "harden off" flowers immediately after harvest by plunging cut stems in water and a carbohydrate such as sucrose, to replace water supplied by the plant. Flowers are then placed in boxes and refrigerated at the lowest temperature possible for each flower variety. Florist cases often maintain relative humidity between 85 and 95 percent to keep flower petals and tissues hydrated and supple. When water touches stems in a bucket or vase, the resuscitation process begins.
  
  

Low Temperature Thresholds

• Author Norah T. Hunter says optimum storage temperature is 32 F, although flowers held for two or three days will keep if stored at 34 to 40 F. When temperatures drop below 32 degrees, ice crystals form in the plant tissue, dehydrating the tissue and piercing the surface. Tropical and sub-tropical flowers such as camellias, orchids, amaryllis, bird of paradise and protea, however, will react to lower temperatures the way roses and lilies respond to freezing; they must be kept in a warmer case cooled only to between 50 and 60 F.
  
  

Other Considerations

• Avoid refrigerating flowers with fruits or vegetables that produce ethylene.Jupiterimages/Photos.com/Getty Images
  
  Although refrigeration and hydration slow respiration, they do not stop it. Refrigerated flowers need light to maintain color and plants give off water, carbon dioxide and ethylene. One of these by-products, ethylene, spurs ripening in fruits and vegetables and maturation in plants. In a florist's case, ventilation removes ethylene. In a consumer's refrigerator, however, a vase of roses set next to a bin containing apples, major outgassers of ethylene, would benefit little from the cooler temperature.