Short answer: Group produce by the temperature it likes. Keep greens cold and wet, keep tomatoes and squash cool but not cold, and keep onions and potatoes dry. Never park ethylene producers next to sensitive crops.
Four zones most trucks can run
Cold. Temperature: 32 to 34°F. Humidity: Above 95%. What goes here: Leafy greens, lettuce, broccoli, cabbage, sweet corn, carrots and other roots, green onions.
Cool. Temperature: 36 to 50°F. Humidity: 85 to 95%. What goes here: Melons (36 to 41°F), peppers (41 to 45°F), summer squash and zucchini (41 to 50°F).
Shelf. Temperature: 50 to 60°F. Humidity: Varies. What goes here: Tomatoes and cucumbers (50 to 55°F), eggplant (50 to 54°F), watermelon (50 to 59°F), sweet potatoes and pumpkins (55 to 59°F).
Dry. Temperature: Room temp, out of sun. Humidity: 60 to 70%. What goes here: Onions, garlic, winter squash.
Steps
Sort your load list into the four zones above before you pack.
Keep ethylene producers (tomatoes, ripe melons, apples, pumpkins) away from sensitive crops (broccoli, leafy greens, cucumbers, eggplant, watermelon). Ethylene speeds up yellowing and spoilage.
Do not over-chill. Tomatoes, cucumbers, eggplant and sweet potatoes pit, soften or lose flavour below their range.
Leave room for air to move. Do not stack boxes tight to the walls or the cooling unit.
Check one thermometer in each zone at load-out and at the first stop. Write it down.
Cut produce is different. Cut leafy greens, cut melons and cut tomatoes must stay at 41°F or below under the FDA Food Code. If you sell anything cut, it goes in the cold zone with a thermometer.
Sources: UGA Extension C1205, Quick Storage Guide for Vegetable Crops · FDA Food Code
