Smokerbill
Crossing the Road
5 years is a good life for the raised bed. Maybe when the structure eventually starts to degrade, you could just build a new bed enclosure around the original structure, and let the old one just compost into the soil.You know, I don't expect my pallet wood raised beds to last a lifetime. I think using untreated pine wood will normally last 3-5 years in a raised bed. I don't know if using the Hügelkultur system will cause the wood to rot out sooner than that. I have 3 hügelkultur raised beds out in my main garden with untreated wood and they are still intact for over 5 years. I have 2 hügelkultur raised beds in my backyard using pallet wood and they are going on their third summer with no signs of wood rot yet. I live in northern Minnesota, and half our year is under snow, so maybe my untreated raised beds just last longer than a raised bed in a more southern state.
I have thought about staining or sealing the pallet wood on the raised bed prior to filling it up. Another idea was to line the inside with empty "plasticy" feed bags and maybe that would add some life to the build because the barrier would keep the pallet wood separated from the soil.
However, I have just decided to leave everything as is for the pallet wood raised beds and actually see how long it lasts before it needs to be repaired, rebuilt, or replaced. A very big factor for me is knowing that I spent less than $1.00 on the hardware for the raised bed, the pallet wood was free, so I did not want to spend much time, money, or energy on trying to make it last a few years longer. It will be easier, and cheaper, for me to just rebuild if needed.
I liked your question, but I really don't know the real answer yet. Maybe someone else has had experience with this issue and could help us both?
I like your idea about using a lining of feed bags on the inside. But if you're getting 5 years might not even be necessary.