rather an expensive use of cocoa shells! i have used them as mulch for many years, and have added spoiled forgotten bags of them to my compost. since they do break down nicely over time, i suppose adding them to container mix might work fine. i have not done that directly, tho, so someone else may have advice for you!

I tried this once in one of my large containers > 10 cu. ft. I usually let mix settle for a day before planting seeds or seedlings. When I went out to plant the next day the container felt hot. It got hotter the further down I stuck my hand. Ended up dumping the entire mix and redoing it. I think I made a post here about it many years ago. I'm usually a sucker for sales and bags of cocoa shells were at get rid of prices so I experimented. I don't think anything would have grown in that container with cocoa shell mix.

I am keeping it in the bag....for now. It seemed like it might be a great thing for containers...but having my doubts.