Saturday, November 22, 2008

Greenhouse - Ethylene Injury From Malfunctioning Heaters

Each year we get problems in production greenhouses due to malfunctioning heaters. The following is an article on ethylene injury that can occur with problem heaters.

Crops grown in greenhouses that utilize gas-fired unit heaters can be susceptible to ethylene injury. Ethylene (C2H4) is an odorless, colorless gas that acts as a plant hormone. Plants are very susceptible to ethylene injury at levels from 0.01 to 1 ppm or more. No other air pollutant causes a greater range of symptoms than ethylene gas. Symptoms range from misshapen leaves and flowers, thickened stems, stunted growth, flower and/or leaf abortion to epinasty. Example pictures of ethylene damage can be found at this web sites:

The effects on greenhouse crops will vary with the plant species and growth stage, temperature, length of exposure, and the concentration of the ethylene. I have noted plant injury symptoms more often in plastic greenhouses compared to glass greenhouses, due to the airtight nature of poly-greenhouses. A good bulletin on the subject was written by faculty at North Carolina State University and is titled Ethylene: Sources, Symptom, and Prevention for Greenhouse Crops. It can be downloaded free at:

An indicator plant to use for ethylene is a tomato plant. They are highly sensitive and will twist or wilt when exposed to ethylene. Tomatoes will exhibit injury within 24 hours if ethylene is present.

To avoid ethylene injury, unit heaters need proper ventilation and intake of fresh air from the outside. One square inch of vent cross section (of outside air) for every 2,500 Btu’s of heater output is recommended. Consider using a laundry dryer vent hose as a fresh air intake. Thus, if you have a 125,000 Btu heater, you would need an 8-inch diameter fresh air inlet pipe that would give you the 50 square inches you need.

Also, unit heaters need to be maintained so that the heater itself is running properly, and the distribution tube, vent stack, ventilation louvers, and fuel line are all functioning correctly.

Reprinted from "Malfunctioning unit heaters can lead to greenhouse crop problems -- check your furnaces!" by Thomas Dudek, District Extension Horticulture Agent, in the January 28, 2005 edition of the Greenhouse Alert Newsletter from Michigan State University Extension.

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