I have previously written a good deal about raised beds made out of raw, untreated wooden planks. I don’t like the idea of building out of pressure-treated wood since I’m not sure if there are any chemicals or salts leaking into the soil. I’ve been using either spruce or pine, I’m not really sure, but I took a picture of the raw planks:

If you know what sort of wood it is, please let me know in the comments.
The raised beds have been outside in the garden for two years now and are beginning to show signs of decay. It’s not really that bad:

It looks like they could last many more years:

But then I took a look at the backside of one of the planks and found this:

It could be that the wood at this spot has been exposed to soil with higher moisture than elsewhere but then again the soil looks the same to me.
I have planned on building three more raised beds out of this type of wood, but now I think it would be better to find some rectangular concrete tiles and place them upright around the edge of the beds. This would be a little more work but the beds could last for centuries.
Now I just have to think of a new project for the planks I’ve already bought.