I have a horse trough about 16 cu ft full of soilless growing material - 5 cubic feet peat moss, 5 cf vermiculite, 6 cf of compost. After a year my compost breaks down so now I have to mix in 6 cubic feet of compost. For the next year, I would like to keep this system going for many years by just adding 6 cf of good compost every year. I guess I want something that breaks down quickly and does not have a lot of useless material (residue) in the compost that is not being used. I have several of these water troughs.
Container gardens will need refreshing and new soil and organic material added after each growing season.
An organic compost material is the best way to do so.