Cut flowers hold vase life at 34–38°F and 85–95% relative humidity. The temperature target is the easy one; the humidity target is where most retail and wholesale floral coolers fall short. A foodservice-profile evaporator strips humidity to 60–75% RH at setpoint; floral chemistry needs 85–95%, and the difference is half the stem life on every order. Hitting the target requires the right evaporator profile, the right controller setup, and operational discipline at the door.
At 100% RH the air is saturated; condensate forms on every surface cooler than the air, including stem petals and packaging. Wet petals develop botrytis (gray mold) and stem ends sit in standing condensate. The 85–95% range holds enough atmospheric moisture to prevent dry-down without crossing into condensation.
Temperature consistency matters as much as the RH number. A cooler swinging 5°F across the day passes through condensation events at the edges even if the average RH is fine. Hold tight on temperature first; humidity follows.
Evaporator temperature differential (TD) is the difference between coil temperature and box air temperature. A foodservice walk-in evaporator runs 18–25°F TD; the coil at 18°F holds box at 36°F. That deep-coil temperature condenses humidity hard.
A floral-grade evaporator runs 5–8°F TD; coil at 28–31°F holds box at 36°F. Less condensation per pass, more humidity left in the air. The trade-off is a larger evaporator with more square footage of coil — that is why purpose-built floral displays cost more than retrofitted foodservice cabinets.
A generic refrigeration tech servicing a floral cooler often resets the controller to factory defaults and does not flag the floral-specific profile parameters. The unit holds temperature; humidity craters; the operator does not notice for two weeks.
After any controller service, verify: setpoint, differential (cycle band), defrost configuration, and evaporator superheat. If the cooler is purpose-built floral, the manufacturer's service documentation has the floral profile parameters — keep a printed copy near the unit.
If the cooler architecture cannot hold 85% RH on its own, supplemental humidification is an option. Ultrasonic humidifiers ($400–1,200) generate a fine mist into the cooler; the evaporator manages the excess. Drawback: scale buildup on coils and electronics if water is hard.
Pinellas County water runs harder than Hillsborough; if you install a humidifier in a Pinellas shop, plan on RO or DI water feed. Otherwise the unit clogs in 6–10 weeks and the coil scales over a season.
Each door cycle exchanges air. Tampa Bay shop air at 75°F and 60% RH brings in less moisture than cooler air at 36°F and 90% RH holds — every cycle dries the cooler. A 200-cycle Saturday strips humidity below 80% by mid-afternoon if the unit cannot recover fast enough.
Strip curtains on walk-ins; door-cycle discipline on reach-ins; bucket placement away from the door. None of these costs anything; all of them help.
A clogged condensate drain re-evaporates standing water inside the box, raising RH past 95% and sweating product. A drain that flows clean keeps RH at design. Inspect drain pan and line monthly; clear stem debris from the strainer.
Summer Tampa Bay shop ambient runs 75–80°F at 55–70% RH. Winter shop ambient runs 68–72°F at 35–50% RH. Cooler load and humidity recovery differ across the year — winter cycles hit RH harder per door event because the incoming air is drier.
Operators who hold 90% RH all summer drift to 75% RH in February without changing anything. Adjust the operational rhythm: tighter door discipline, more bucket coverage, and supplemental humidification turned up in winter.
85–95% RH at 34–38°F is the standard for most commercial cut flower varieties. Roses, lilies, hydrangeas, alstroemeria, gerberas, mums all hold to that profile. Tropicals (orchids, anthuriums, birds of paradise) hold at 50–55°F at 60–80% RH — different regime, separate cabinet.
The evaporator runs a foodservice TD profile (18–25°F differential) that strips humidity. To hold 90% RH you need either a low-TD evaporator (5–8°F differential, requires a larger coil and sometimes a different unit) or supplemental humidification. The controller alone cannot fix it.
No. Cycling the evaporator off lets temperature drift, which is worse for stem life than 75% RH at consistent 36°F. Hold temperature; fix humidity with the right hardware.
Suncoast Cold Systems services floral and agricultural refrigeration across Tampa, St. Petersburg, Clearwater, Brandon, Riverview, Temple Terrace, and Wesley Chapel — retail floral display coolers, wholesale floral DC walk-ins, ag packing-shed cold rooms, hydrocoolers, and forced-air cooling tunnels. 24/7 dispatch. Licensed Class A A/C Contractor (FL #CAC1824642), EPA 608 Universal, OSHA 30 Construction.
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