Most nursery containers are reusable. Charging a deposit (for example 10 cents per cell, refundable if returned within 30 days of plant delivery) or otherwise encouraging clients to return containers saves money and resources. Reusable containers usually have some residual growing medium or pieces of roots that could contain pathogenic fungi. Seedling roots sometimes grow into the pores of containers with rough-textured walls, such as Styroblock™ containers, and remain after the seedling plug has been extracted (figure A). Liverworts, moss, and algae also grow on containers and are very difficult to remove from reusable containers. Used containers should be washed first to remove old growing media and other debris. If available, a pressure washer is excellent for this purpose. Otherwise, a regular hose, or a soak in a garbage can followed by a rinse with a hose, works too.
Next, the containers should be sterilized. Because many tropical nurseries choose not to use pesticides and chemical disinfectants, hot-water dips are the most safe, environmentally friendly, and effective way to kill fungi and other pests in used containers. Most pathogens and weed seeds are killed when containers are held at 158 to 176 °F (40 to 60 °C) for more than 3 minutes (figure B). A good rule of thumb is to use a soaking temperature of 165 to 185 °F (75 to 85 °C) for 30 to 90 seconds for Styrofoam™ containers; 15 to 30 seconds is probably sufficient for hard plastic containers (Dumroese and others 2002). Soaking Styrofoam™ at hotter temperatures can cause the material to distort. Commercial units are available, but many nurseries have built homemade container dipping systems that hold the containers under hot water in a dip tank.
Other options for sterilizing containers and nursery tools include using household bleach or alcohol. These chemicals are phytotoxic to plants and should never be used on or near seedlings. For bleach, use regular household bleach (5.25-percent sodium hypochlorite concentration), diluted 1 part bleach to 9 parts water. Dip or soak the containers and tools in this bleach solution; then rinse them well before using. If the diluted bleach is stored in a covered container, such as a garbage can with a good lid, the solution may be used again, as long as it has not lost its strength. Wood, grain, or rubbing alcohol (70 to 100 percent) may also be used to sterilize containers and tools. Alcohol is used full strength. Dip or soak the containers and tools in the alcohol, but do not rinse them. Allow the containers and tools to dry in the air before using them. (Taken by permission from “Tropical Nursery Manual” by Thomas d. Landis, Tara Luna, and R. Kasten Dumrose)