I have watched many YouTube videos from Gardening With Leon. Essentially, he is making a sub-irrigated planter in a tub instead of a raised or elevated bed. He prefers to use perforated drain pipes or empty plastic containers. The idea is to maximize the water holding capacity of the tub in the bottom as the water fills the plastic containers.and Gardening With Leon about bucket and tub gardening that looks simple enough for me.
If you use wood chips instead of plastic containers, like we have been discussing, the wood will take up physical space and not be able to hold as much water as an empty container. But, it still will hold lots more water than a planter that has drain holes on the bottom and the water is just allowed to run through. The plastic containers will probably last forever, but the wood chips will slowly break down and decompose, feeding the plants as they decompose.
There is a guy on YouTube that gives yearly updates on his hügelkultur pots. He dumps out all the contents and looks at how the wood is breaking down. I think after his third year, he said he was going to recharge the wood as he rebuilt the planter. So, that might give you some idea of how long the wood chips would last. In theory, as the wood decomposes, it becomes more sponge-like and retains even more water. But, I would assume that at some point the wood breaks down to a point where it would have to be replaced.
Leon is all about using a number of different fertilizers in his planters. I am not opposed to this as the potting soil in these type of planters is not a true living biome. I just don't know much about fertilizers myself as I have mostly planted in the ground until the recent 5 years. And now I am mixing the chicken run compost into the garden beds with the idea that it will act as a natural fertilizer.
Leon has a saying that I have heard many times on his various videos. "You only need to feed the plants on the days you eat." He really believes in boosting production with fertilizers.