The orchard thermometer is a mineral spirit-filled thermometer designed to give accurate observation of minimum temperatures in citrus areas; bigger than most standard thermometers, the large scale Fahrenheit degree minimum-type thermometer of liquid-in-glass is easy to read and durable; the large red index inside the thermometer’s glass tube gives lowest air temperature in same manner as with United States National Weather Service (USNWS) Official Minimum Air Thermometer where the index lowers with the column of red-colored mineral spirits (the liquid contracts as temperatures drop), then stays in place when temperatures rise and the column expands back up the glass tube, The location of the index indicates the minimum temperature. The open design of the white plastic shield is meant to emulate overhead tree foliage and shades the thermometer from direct sunlight. The open face of the shield faces north at our latitude. Orchard thermometers are inexpensive and can be purchased from most nurseries around the United States for well under 40 dollars.
Farmers used to use the orchard thermometer to keep track of freezing temperatures. Freezing temperatures have a negative effect on orchards, and farmers often use furnaces to keep temperatures around the their trees above 32 degrees Fahrenheit. These days, automated stations can be set up in orchards that not only keep track of temperatures, but are capable of ignited furnaces throughout the orchard automatically when a pre-determined temperature is reached.
~ Steve Woodruff and Devin Lussier