The following is a short article on reusing containers in the greenhouse.
While some growers clean and re-use pots, trays and flats and it is important to do it properly. Plant pathogens such as Pythium, Rhizoctonia and Thielaviopsis can survive in root debris or soil particles on greenhouse surfaces. If the previous crop had a disease problem, then avoid re-using those containers. It is also a good idea to avoid planting crops that are prone to Thielaviopsis problems, like pansies, in containers that have been previously used.
All containers should be washed thoroughly to remove soil particles and plant debris before being treated with a greenhouse disinfectant, even if there was no evidence of disease in the crop. Debris and organic matter can protect pathogen spores from coming in contact with the disinfectant solution.
There are several products available for disinfecting surfaces including quaternary ammonium products (Greenshield®, Physan 20™, Triathlon®), and hydrogen dioxide (ZeroTol®, OxiDate®). Follow label directions for these products - labels indicate that pots must be soaked for at least 10 minutes in these products to be fully effective. A 10 percent solution of household chlorine bleach (one part bleach to 9 parts of water) may be used for pots and flats, but the solution has a shorter activity period than other disinfectants, losing half its strength in 2 hours. Chlorine bleach is also phytotoxic to some plants, and must be used in a well-ventilated area to protect workers
Information from the New England Greenhouse Update Website http://www.negreenhouseupdate.info/index.php/updates