Gardening in the ground and gardening in containers are two different things. Much of what works in one culture is not beneficial or can even be harmful in the other. If you were to turn a cover-crop under in a container, the plant matter would be situated in a nearly all organic mix that's high in water content and heavily colonized by rot causing bacteria just waiting for you to set the table with a fresh batch of nitrogen-rich plant matter. The results: Since the plant matter would be almost completely unsuberized (nothing to stop decay organisms from immediately cleaving hydrocarbon chains) near instant cellular breakdown of the plant material would occur, causing it to turn to a thick, soup-like consistency. A large dose of N would be immediately available for plant uptake, but would soon be leached from the soil with the regular watering required in container culture. The short-lived benefit of a surge in N would likely be more than offset by the fine particles of rotting vegetation clogging air spaces in the soil, which could easily lead to rotting of plant roots.

Before I add anything to a container soil, it must pass the porosity test. I ask myself if the material could have an adverse effect on drainage/aeration. If the answer is YES, I can find no good reason to use it. There are too many good materials/products out there that do not compromise drainage/aeration to use any that do. The only possible benefit a cover crop would have in a container soil is a N boost. The rest of what occurs would be deleterious rather than beneficial. There are hundreds of organic and inorganic vehicles by which N can effectively and efficiently be added to soils other than cover crops or grass clippings.

Al

Wow! Thank you for the education! I could've made a mess of my barrels! I guess I'll just mix in some compost and then mulch the top. And maybe some of that osmocote time-released stuff?