Q: I did container gardening this year and used a lot of potting soil for tomatoes, peppers, cucumbers, spinach and romaine. Should I discard all of the potting soil or can I use some of it next year?
A: Two things happen to potting soil over time. First, the peat moss it contains breaks down into smaller particles. This causes poor drainage. Second, the soil may collect fungal spores and insect eggs. If you are confident the plants from this year didn’t harbor disease or bugs, you can probably re-use the soil without problems if you restore its capacity to drain well. Dump it all out on a tarp and mix it 4:1 with ground pine bark fines or perlite. I would not re-use potting soil more than twice.