Greenhouse - Reducing Heating Costs II

This is the second in a series on reducing heating costs in greenhouses. This post focuses on increasing the efficiency of heating systems.

Efficient Heating Systems

• Installation of floor or under-bench heat will allow air temperature to be set 5º - 10ºF lower.
• Yearly maintenance - Check boiler, burner and backup systems to make sure they are operating at peak efficiency. Have furnaces cleaned and adjusted and an efficiency test run before heating season. A 2% increase in efficiency for a 30' x 150' greenhouse will save about 200 gallons of fuel oil or equivalent in propane.
• Clean heating pipes and other radiation surfaces frequently.
• Check accuracy of thermostats - correcting a reading that is 2ºF high will save $100-$200.
• Install electronic thermostats or controllers with a 1 ° F accuracy. Potential yearly savings of 500 gallons of fuel oil or equivalent in propane in a 30' x 100' greenhouse when changing from a mechanical to electronic thermostat or controller.
• Aspirate thermostats or sensors for more uniform temperature control. Differential between on and off can be reduced as much as 6ºF.
• Install horizontal air flow (HAF) fans to get more uniform temperature in the growing area.
• Insulate distribution pipes in areas where heat is not required.
• Check and repair leaks in valves, steam traps and pipes.

Reprinted from "Greenhouse Energy Conservation Checklist" by John W. Bartok, Jr., Agricultural Engineer, Natural Resources Mgt. & Engr. Dept., University of Connecticut , Storrs CT

Greenhouse - Weed Control and Herbicide Use in Greenhouses

Summer sales are ending and poinsettia planting season has not started in greenhouses. Now is the time to perform maintenance in empty greenhouses. Remove all plant materials, do not keep a few plants in an otherwise empty house. By shutting down fans for a few days, you can solarize a house and kill many insects and other pests with the high temperatures that develop. Remove all weeds before they go to seed. Apply control measures to weeds growing on greenhouse floors and walkways. This includes certain non-selective herbicides with limited residuals. The following are your options:

Herbicides labeled for use in greenhouses. These herbicides are intended for use under greenhouse benches and walkways and not for use in pots.

1) Diquate (Reward and others), 0.75 oz (22 ml) per gallon of water, Controls all emerged vegetation to which solution is applied. Need to add surfactant to spray solution.

2) Glufosinate (Finale) 3-4 oz (89-118 ml) per gallon of water, Controls all emerged vegetation to which solution is applied. Make sure that circulation fans are turned off during application. When making application, be sure to use low pressure nozzles that produce larger droplets. Do not use in greenhouses with food-producing crops.

3) Glyphosate (Roundup Pro and others), 2.5-6.5 oz (75-190 ml) per gallon of water. Make sure to use a glyphosate product that contains 42% or greater active ingredient. Controls all emerged vegetation to which solution is applied. If used in the greenhouse, fans must be off and all desirable vegetation must be removed from the greenhouse.

4) Pelargonic acid (Scythe), potassium salts of fatty acids, 1.3-13 oz (38-384 ml)per gallon of water. Controls all emerged vegetation solution comes in contact with. Avoid contact with desirable plant material. When making application, be sure to use low pressure nozzles that produce larger droplets.

*1 oz = 30 milliliters (ml).

Do not use any other herbicides in greenhouses unless labeled. Many residual herbicides will volatilize in a greenhouse environment leading to injury on subsequent greenhouse crops. This could potentially render greenhouses unusable for a period of time.

Information taken in part from "Weed Control in Greenhouses" by Mark A. Czarnota, Extension Horticulturist, University of Georgia.

Greenhouse - Time to Clean Out Houses

Summer sales are ending and poinsettia season has not started. Now is the time to perform maintenance in empty greenhouses. The following are some maintenance actions to consider:

• Remove all plant materials, do not keep a few plants in an otherwise empty house
• Remove all weeds before they go to seed.
• By shutting down fans for a few days, you can solarize a house and kill many insects and other pests. Be carefull that you do not damage any materials that could melt with the high temperatures.
• If houses are completely empty, you can spray existing weeds with glyphosate. However, be careful that no material is vented out where it can affect plants growing outside or can be drawn into other houses. It is best to shut off fans and spray in early morning.
• Repair or replace landscape fabric on floors.
• Spray all bench surfaces with disinfectants.
• Replace greenhouse plastic film if needed.
• Have heaters serviced before the fall heating season.
• Do any necessary painting, replace any insulation as necessary
• Check all irrigation systems for leaks and make repairs

Gordon Johnson, Extension Horticulture Agent, UD, Kent County