Monday, January 27, 2014

Reusing Potting Soil


When replanting in containers, should the old potting soil be recycled?
Reusing potting soil can work for a while; it can be rejuvenated each time by adding some nutrients and perhaps some organic matter. If a pathogen, however, whether fungal, bacterial or nematode, is introduced by way of an infected plant, the whole pot is contaminated and subsequent plantings are at risk of being infected. Have you ever planted seeds in a container and nothing comes up?  This is one reason why. 

Sanitation is important both for commercial operations as well as for the backyard. Buying new potting mix each time is the best solution. Since this can become costly, the question arises, “Can I clean up or sterilize used soil?” Here are three methods:
1) Solar sterilization, putting clear plastic over a pile of soil and allowing it to bake for 4-6 weeks, is a good idea in some locals since warm weather is required. 2) Steam sterilization is quite effective, but one must have access to steam. 3) Lastly, and perhaps the most practical for small quantities of mix is the oven. Here are the directions: place slightly moistened soil mix in a covered pan and bake in the oven at 250 degrees F for about 45 minutes.  The center of the mix needs to reach a temperature of 180 degrees F for at least 30 minutes; use a candy or meat thermometer to check the temperature.  This process may produce an unpleasant odor.  

Used potting soil can be thrown in a garden compost pile. Alternatively, a designated pile of used potting soil only can be created. When the process is complete, the soil is able to be reused for container purposes. This procedure will be relatively safe if either compost pile heats to proper temperatures, and the heating is uniform. Ideal temperatures range from 104 F. for 5 days to 130 F. for 4 hours. 

If potting soil is reused, I would recommend a type of crop rotation. Whether vegetables or annual flowers, replanting with the same species of plant or even in the same family is not advisable. For the next planting, rejuvenate the soil and plant with a different family of plants. In conclusion, gardeners have been successful in reusing soil mixes; nevertheless, the above information is useful for making an informed decision.