Any idea on suppliers? Most of the ones I've seen online don't specify heart or sapwood
||If you can, buy from a local sawmill and make sure of what you are getting. I use a supplier in Surrey, Homewoods. Not sure if he does what you want or if he supplies that far away, but we have been happy with the sawn oak posts and roundwood chestnut posts he has supplied us over several years. The roundwood may contain sapwood as well, but most of it is taken off with the debarking I think, and by the nature of the shape, you only lose a small amount round the outside with time.|
||There's a chestnut woods round here but he seems to be more interested in firewood than timber. I'll have a hunt|
||Might be worth asking. If you want round poles, all you need to do is debark them and they should be quite suitable. They are usually grown to 4-8" before felling and if he has some poles with the right length of straight in for your needs, he might be willing to sell you a few to process yourself.|
Oak will last for ever pretty much. Chestnut has a soil contact life of about 25 years.
Chestnut tends to be managed by coppice and will likely be more sustainable.
If it was me, I would use Chestnut.
||I would expect both to last about 20 years, but make sure you get all heartwood as the sapwood tends to rot.|