Smudge pot

A smudge pot is an oil-burning orchard heater that releases heat and smoke during freezing weather to help protect crops from frost.

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Radiation frost: A freeze caused when the ground and nearby objects lose heat by radiation under clear, calm skies. Smudge pots are most useful during this kind of frost, when warm air can remain above the orchard.
Frost protection: Methods used to reduce damage to plants from freezing temperatures. Smudge pots are a direct-heating method within this broader practice.
California citrus industry: The commercial cultivation and processing of citrus fruit in California. Citrus growers helped establish large-scale use of smudge pots against damaging freezes.
Passive frost protection: Preventive measures that reduce freeze risk without adding heat during the frost event. Site selection and cold-air drainage can reduce the need to operate smudge pots.
Temperature inversion: An atmospheric condition in which air temperature rises with altitude through a layer. During an inversion, heaters can mix warmer air down toward crops.
Wind machine: A powered orchard device that mixes warmer air aloft with colder air near the ground. Wind machines exploit inversions without burning fuel at each tree.
Citrus greening: A bacterial disease that disrupts citrus growth and causes fruit to become misshapen and bitter. The disease has made some frost-protection investments less attractive in affected orchards.
Microsprinkler irrigation: A localized irrigation method that applies water around plants through low-flow emitters. Some growers use it for freeze protection with less atmospheric smoke.
Combustion: A chemical reaction in which a fuel reacts with an oxidizer, releasing heat and often light. Burning oil supplies the heat that makes a smudge pot an orchard heater.
Overhead irrigation: A crop-protection method that sprays water over plants during freezing weather. Water’s release of latent heat can protect blossoms by a different physical mechanism.