The use of cold temperatures is a fundamental strategy for extending the life of cut flowers, slowing the natural aging process that begins the moment they are harvested. Refrigeration preserves freshness by minimizing metabolic activity and reducing the rate at which the flower consumes its stored energy reserves. However, this beneficial effect operates within a narrow band; temperatures that are too low can rapidly shift from preservation to destruction. Understanding this fine line is necessary to maximize the longevity of blooms.
Distinguishing Chilling Injury from Freezing Damage
Cold temperatures shorten a flower’s life through two distinct mechanisms: chilling injury and freezing damage. Chilling injury is a physiological disorder occurring at non-freezing temperatures, typically 32°F to 59°F (0°C to 15°C), depending on the species. This damage is common in tropical flowers and symptoms often appear later, after the flower returns to a warmer environment, manifesting as water-soaked spots, browning, or a failure of buds to open properly.
Freezing damage occurs when the temperature drops below the freezing point of the flower’s tissue, usually slightly below 32°F (0°C). This damage is immediate, physical, and irreversible. Upon thawing, affected tissues become limp, translucent, or blackened, indicating total cell death. The presence of ice crystals is the defining factor for freezing damage.
Cellular Basis of Cold-Induced Deterioration
The dysfunction observed in chilling injury begins within the cell membranes. For chilling-sensitive plants, exposure to low, non-freezing temperatures causes the lipid components of the cell membranes to undergo a phase transition. The flexible, liquid-crystalline structure converts into a rigid, solid-gel state, which profoundly disrupts the membrane’s function and alters permeability.
This structural change compromises cell integrity, leading to metabolic imbalances and the leakage of electrolytes. Freezing damage, however, results from the physical presence of ice crystals. Water outside the cell freezes first, creating an osmotic gradient that draws water out, causing severe dehydration and collapse. If cooling is rapid, ice crystals can form inside the cell, which is nearly always fatal as the crystals physically rupture the organelles and cell wall.
Maximizing Flower Longevity Through Temperature Control
The optimal temperature range for storing most temperate cut flowers is precise, typically 33°F to 36°F (0.5°C and 2°C). This range is low enough to significantly slow the flower’s respiration rate and minimize ethylene production. Crucially, it is high enough to reliably avoid the formation of damaging ice crystals, extending the usable life for days or weeks.
The duration a flower can be held in cold storage is highly species-dependent. Cold-tolerant flowers like roses and carnations can sometimes be stored for up to 12 weeks at temperatures near 31°F (-0.6°C) with proper pre-storage treatments. This technique is often used in the commercial floral industry to manage supply for peak demand periods.
Tropical Flower Storage
Species variability is a primary consideration, as not all flowers tolerate the same cold. Tropical flowers, such as orchids, gardenias, and bird of paradise, are highly sensitive to chilling injury. These varieties require a much warmer environment, with optimal storage temperatures often set between 50°F and 55°F (10°C and 13°C). Storing these cold-sensitive varieties in the same cooler as temperate flowers will lead to their premature decline.