Heated greenhouses and high tunnels are designed to protect crops from the elements. But a poorly maintained heating system may actually damage plants by creating air pollution, according to a Penn State University Extension newsletter.
Steve Bogash, a commercial horticulture educator, said he visited a number of facilities with plant damage this season.
Tomatoes are very sensitive to ethylene, sulfur dioxide and nitrogen oxides—all by products of combustion.
The prolonged spring cold period has added to existing problems of poorly vented, unvented or poorly engineered heating units.
The problem is more prevalent in high tunnels, where heaters are often an afterthought and used only to prevent temperatures from dropping below 45 degrees Fahrenheit at night.
Diagnosing pollution-induced plant injury can be difficult and confusing.
Plants vary on their sensitivity to pollutants and to specific gases.
Sensitivity also is affected by light intensity, plant age, time of day, humidity, and water and nutrient status.
High humidity in a well-watered plant, for example, increases the likelihood of damage as the stomata are open and allow pollutant gases to enter.
The safest way to run heaters is to have them outside of the growing area and use hot water from the boiler pumped through fin tubes and radiators to heat the planted area, Bogash says.
In addition, inspect heaters regularly, follow manufacturers' maintenance instructions, keep chimneys in good condition, and avoid use of temporary, free-standing heaters such as salamanders.
Read more about diagnosing pollution-induced symptoms at Penn State University.