3 Areas of the Greenhouse That Need to be Ready Before School Starts

June 15, 2016

3 Areas of the Greenhouse That Need to be Ready Before School Starts

I pulled the following information from an email sent from Dr. Teri Hamlin a few years back. She's a former North Region horticulture teacher in Georgia.  Start work now to make sure your greenhouse is in proper order for when school starts back in the fall.


Floors should be disinfected: Begin by thoroughly cleaning the floor of soil, organic matter and weeds and removing the residue from the greenhouse.

Benches should be disinfected and pots, flats, and trays should be new or disinfected. Disinfect benches by mixing one of the below disinfectants in a sprayer and spraying all surface areas of the bench, flats and pots.  Please make sure you wear all the proper PPE and follow all the necessary procedures before handling disinfectants. 

Disinfectants for Greenhouses

There are several different types of disinfectants that are currently used in the greenhouse for plant pathogen and algae control. All these products have different properties. If possible, disinfectants should be used on a routine basis both as part of a pre-crop clean-up program and during the cropping cycle.

  • ammonium compounds (Green-Shield, Physan 20, and Triathlon), hydrogen dioxide (ZeroTol, Oxidate)
  • chlorine dioxide (Selectrocide) 
  • chlorine bleach
May teachers use chlorine bleach. There are more stable products than bleach to use for disinfecting greenhouse surfaces. However, when used properly, chlorine is an effective disinfectant and used for many years by growers. A solution of chlorine bleach and water is short-lived and the half-life (time required for 50 percent reduction in strength) of a chlorine solution is only two hours. After two hours, only one-half as much chlorine is present as was present at first. After four hours, only one-fourth is there, and so on. To ensure the effectiveness of chlorine solutions, it should be prepared fresh just before each use. The concentration normally used is one part of household bleach (5.25 percent sodium hypochlorite) to nine parts of water, giving a final strength of 0.5 percent. Chlorine is corrosive. Repeated use of chlorine solutions may be harmful to plastics or metals. Objects to be sanitized with chlorine, (hand tools, pots, and trays) require 30 minutes of soaking and then should be rinsed with water. Bleach should be used in a well-ventilated area. It should also be noted that bleach is phytotoxic to some plants, such as poinsettias.


Managing Algae

Algae growth on walks, water pipes, equipment, greenhouse coverings, on or under benches and in pots is an ongoing problem for growers. Algae form an impermeable layer on the media surface that prevents wetting of the media and can clog irrigation and misting lines, and emitters. It is a food source for insect pests like shore flies, and causes slippery walkways that can be a liability risk for students. To avoid algae build up keep walks sweep clean and free of puddling water. Reduce the flow of water in your evaporative cooling system with your gate value. You only need enough water flow to get the pads wet and should not have water splashing off of the system. You may also choose to adjust the greenhouse thermostats slightly to that during the night the cooling cell shuts down and can dry.  This down time will limit and some cases prevent algae growth.  The recommended disinfectants can be used to spray on floor where algae is appearing.

Irrigation Systems

Non-recirculating irrigation systems can be cleaned using a new product, chlorine dioxide (Selectrocide). It is labeled for disinfecting irrigation lines and greenhouse surfaces. To thoroughly clean irrigation systems, the company recommends using two consecutive overnight treatments, and then flushing the system with clear water, making sure to discard the dislodged debris. Selectrocide can also be used as a continuous ultra-low dose treatment.


While cleaning and disinfecting isn't the most glamorous activity the work put in now will pay dividends during the school year.  You may even enlist the help of some of your students to come in and help you complete the process.  One or more students could even turn the project into a greenhouse manager SAE with a little arm twisting.

Good luck with this and please let us know your thoughts.  Please follow us on FacebookPinterest, and Twitter. Send us your Facebook, Twitter, and Pinterest handles and we'll be glad to follow as well. You can also contact me at brian@onelessthing.net