Read up some on compost for the potting mix. Did not use compost except for a couple handful's of black cow on the top layer of the container. Probably was not enough. Checked the garden supply and may use mushroom compost. Might just forget the 20 gallon mulch bin and buy the compost.
I still will get a bale of straw to layer the top of the soil. They say that is a helpful benefit for container gardening.

Never really gave compost much thought when I done the containers for transplanting.

A thought occurred to me about ten minutes ago from back on the farm. My father use to plant winter wheat in the fall and when spring time came it got up a ways and he plowed it under. He probably told me why back then but I can not remember why he did it. It has been 60 years since my farm childhood days and leaving for the military.
No doubt the winter wheat was plowed under as green compost.