
A smudge pot (also known as a choofa or orchard heater) is an
oil-burning device used to prevent
frost
Frost is a thin layer of ice on a solid surface, which forms from water vapor that deposits onto a freezing surface. Frost forms when the air contains more water vapor than it can normally hold at a specific temperature. The process is simila ...
on
fruit trees. Usually a smudge pot has a large round base with a chimney coming out of the middle of the base. The smudge pot is placed between trees in an
orchard
An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit tree, fruit- or nut (fruit), nut-producing trees that are generally grown for commercial production. Orchards are also so ...
. The burning oil creates heat, smoke, carbon dioxide, and water vapor. It is believed that this oil burning heater will help keep the orchard from cooling too much during the
cold snaps.
History
In 1907, a young inventor, Willis Frederick Charles “W.C.” Scheu (Dec 1st, 1868April 11th, 1942), at that time in
Grand Junction, Colorado, developed an oil-burning stack heater that was more effective than open fires in heating orchards and vineyards. In 1911, he opened Scheu Manufacturing Company in
Upland, California, and began producing a line of orchard heaters. Scheu Steel is still in business, in 2021. The use of smudge pots became widespread after a disastrous freeze in Southern
California
California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
, January 4–8, 1913, wiped out a whole crop.
Smudge pots were commonly used for seven decades in areas such as
California
California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
's numerous citrus groves and vineyards. The
Redlands district had 462,000 orchard heaters for the winter of 1932–33, reported P. E. Simpson, of the supply department of the
California Fruit Growers Exchange, requiring 3,693,000 gallons of oil for a single refilling, or about 330 tank car loads. To fill all of the smudge pots in Southern California one time required 2,000 car loads.
Smudge pot use in
Redlands, California
Redlands ( ) is a city in San Bernardino County, California, United States. As of the 2020 United States census, 2020 census, the city had a population of 73,168, up from 68,747 at the 2010 United States Census, 2010 census. The city is located a ...
groves continued into the 1970s, but fell out of favor as oil prices rose and environmental concerns increased. Pots came in two major styles: a single louvered stack above a fuel-oil–filled base, and a slightly taller version that featured a
cambered, louvered neck and a galvanized re-breather feed pipe out of the side of the chimney that
siphon
A siphon (; also spelled syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in an inverted "U" shape, which causes a liquid to flow upward, abo ...
ed stack gas back into the burn chamber and produced more complete
combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...
. The return-stack heater was developed by the
University of California
The University of California (UC) is a public university, public Land-grant university, land-grant research university, research university system in the U.S. state of California. Headquartered in Oakland, California, Oakland, the system is co ...
and became commercially available about 1940. Filler caps have a three- or four-hole flue control. The stem into the pot usually has a piece of oil-soaked wood ("down-draft tube and wick")
[Leonard, A. S., and Kepner, Robert A., "Return-Stack Orchard Heater", ''California Agriculture'', June 1950, page 9.] secured inside the neck to aid in lighting the pot. Pots are ignited when the air temperature reaches , and for each additional degree of drop, another hole is opened on the control cap ("draft regulator").
Below 25 degrees, nothing more can be done to enhance the heating effects.
Types and usage

Some groves used
natural gas
Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
pots on lines from a gas source, but these are not smudge pots in the usual sense, and they represented only a fraction of the smudging practice. Experiments using natural gas heaters were conducted in
Rialto, California, in 1912. Sometimes, large smudge pots are used for heating large open buildings, such as mechanics' workshops. In
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
they are called "choofers" because of the noise they make when lit: "''choofa choofa choofa''".
Lighting an Australian "choofer" is a tricky business. Because of the voluminous clouds of oily black smoke they produce when cold, they must be lit outside. This is accomplished by holding a burning rag next to the open damper on the fuel tank. The draught caused by the breeze passing through the chimney will draw air through the open damper into the fuel tank, where the surface of the fuel inside will light and burn instantly. Once the choofer is sufficiently warm, the damper may be closed until a steady rate of burning is attained, when the characteristic "''choofa choofa choofa''" noise is produced. If the damper is not closed, the choofa may choke itself with its own smoke, causing periodic "explosions" of unburnt gases in the chimney. Such explosions are not dangerous, but they are noisy and they produce a lot of smoke. Once the heater is burning hot enough, the smoke will disappear and the pot may be dragged slowly and carefully inside. They still produce dangerous gas and must only be used in well-ventilated spaces.
Choofers will burn almost any combustible
liquid fuel
Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy, usually producing kinetic energy; they also must take the shape of their container. It is the fumes of liquid fuels that are flammable ...
, including
kerosene
Kerosene, or paraffin, is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from the Greek (''kērós'') meaning " ...
,
diesel fuel
Diesel fuel, also called diesel oil, heavy oil (historically) or simply diesel, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a re ...
, or used
sump oil
Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists ...
.
Prior to the development of battery-powered safety blinkers on saw-horses, many highway departments used small oil-burning safety pot markers to denote work zones, and many railroad systems still rely on oil-fired switch heaters, long tubs of fuel with a wicks, that fit between the ties and keeps snow and ice from fouling the points of a switch. This is generally only used in yard applications. Mainline switches are usually heated by natural gas heaters.
The smudge pot was also used at construction sites and other cold places to take the chill out of buildings so workers would be comfortable, and for several decades (1920s–1970s) they were used as emergency night landing illumination at remote airfields without electric runway lights, acting as a series of small bonfires.
Use in war
Smudge pots were used by the Germans, the Japanese, and the United States Navy during
World War II
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, and by the North Vietnamese in their invasions of Laos during the
Vietnam War
The Vietnam War (1 November 1955 – 30 April 1975) was an armed conflict in Vietnam, Laos, and Cambodia fought between North Vietnam (Democratic Republic of Vietnam) and South Vietnam (Republic of Vietnam) and their allies. North Vietnam w ...
to protect valuable targets.
The oily black clouds of smoke produced from these smudge pots was intended to limit the ability to locate a target. In Vietnam, smoke from smudge pots was used as a defense against
laser-guided bomb
A laser-guided bomb (LGB) is a guided bomb that uses semi-active laser guidance to strike a designated target with greater accuracy than an unguided bomb. First developed by the United States during the Vietnam War, laser-guided bombs quickly pro ...
s. Smoke would diffuse the laser beam and break the laser's connection with its intended target.
Other significance
* The smudge pot often became a symbolic prize in Southern California high school football rivalries.
**
Bonita High School and
San Dimas High School, affiliated with the
Bonita Unified School District in
Southern California
Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...
, compete in varsity football for a silver-plated smudge pot.
**In
Redlands, California
Redlands ( ) is a city in San Bernardino County, California, United States. As of the 2020 United States census, 2020 census, the city had a population of 73,168, up from 68,747 at the 2010 United States Census, 2010 census. The city is located a ...
,
Redlands High School and
Redlands East Valley High School also compete in varsity football for a blue-and-red smudge pot. The game is known among football fans as the 'Smudge Bowl'
*Sometimes called a "highway torch", smaller smudge pots were historically used to warn oncoming traffic of road maintenance at night.
See talk''">Talk:Smudge_pot#Highway_torch,_Toledo_torch">See talk''/sup>
References
{{Reflist
Fireplaces
Gardening aids