I grow a lot of annual edible plants in containers and since I am using soil that I purchased in order to increase the nutrient content and soil life, I usually place plant matter at the bottom of my pails then fill it up with soil. This is an ongoing thing I do to always improve the quality of soil in containers.
The plant material does break down usually after a few months unless they are larger particles which I just wait.
During the winter months, I do soil shoots in those 10 inch black containers, (mostly radish & buckwheat) and after cutting down my shoots, I place the rest of the plant material at the bottom of the next container I will use and fill with soil. This breaks down very quickly.
Another thing I do is when composting in 5 gallon pails over the winter in a heated outbuilding, whatever is not completely composted, but lets say it is about 75% composted at the end of winter, I will add that to the bottom 2 inches of my containers mixed with some soil, then add soil to fill the container and then I plant in it.
I started doing this because I would have more pots for planting in. If I did not do this, I would only have 12 pots to plant in, but doing this, with the same amount of soil & non composted or mostly composted organic matter at the bottom of each pot, I could now do about 17 pots.
This seems to be working just fine.