Good species for fence posts
Rot resistance of red oak, white oak and more. February 6, 2002
I am looking at using either red or white oak for fence posts. How do these species compare in regards to rot resistance? The fence will be in a humid environment.
Between the two, white is more rot resistant than red.
White oak is much better. Also, don't use chestnut oak.
I wouldn't use either red or white oak for fence posts. The white oak will last longer, but for the cost of putting up a fence, you might better use pressure treated or locust if it is available.
Not even close... white oak will last longer every time. I have white oak posts in the ground with no preservatives that are in great shape after 15 years. I tried northern red oak and was not able to get much more than 7 years before they decayed to the point that they were no longer useful.
Chestnut oak is the only white without, or at least with very few, tyloses. Perhaps the same leak-proofing that tyloses give to most white oaks slow fungi down, giving them their decay resistance, or maybe there's something else going on?
A vouch for locust if available. There are posts here in Ohio that have been in the ground longer than I've been around--39 years. They have outlasted phone poles and railroad ties.
Eastern white cedar posts work good, too. There are cedar posts that have been in the ground for 80+ years on our farm and they are still solid. The region that you are from will more than likely dictate what you will have available and use.
Grandpa always says "Red oak never lay it down, white oak stick it in the ground." Just make sure that the post is clean of bark and we dip the end in used oil for good measure. Have posts on the farm that Grandpa skinned by hand and put in green back in the 40's that are still there.
I am not a supporter of pressure treated. I have seen many instances of pressure treated rotting in ten years. White oak will without a doubt outlast pressure treated. I would much rather have a sliver from oak than treated. One of the chemicals in them is arsenic. I read that over 100 deaths a year are caused from pressure treated. As for red oak, I don't even know why it is called oak.
In California, our redwood - the "white wood" is worthless in the ground but the heart or red will last a very long time. Older growth trees are much better and there are redwood posts and "footings" that have been in the ground for over 100 years and still are as good as day one.
As far as the pressure treated, the light green stuff is usually worthless due mostly to the fact it comes from cheap wood, but acza treated fir, dark black/green, works very well and if handled properly is safe.
Eastern red cedar will last in the ground as well as any of the others. I have some that are 30 + and are doing fine.
I would never advocate the use of PT to be used around humans. The problem is that it is used for decks, picnic tables and children's play equipment. I also understand that they have or are going to remove the arsenic in PT lumber. There are different grades of PT - some is for above ground and some is for below ground. I have built miles of horse fencing and have PT posts in the ground for over 20 + years without having them rot. Some companies pressure treat and some just green color the wood. Check with your local lumberyard for a flyer on the proper uses and safe handling of PT.
There is no mention of what kind of fencing the posts are being used for - barbed wire, railor picket. It is not hard to replace a post on barbed wire, but it becomes a costly project on rail fences.
The type of soil will also contribute to how long a post will last in the ground. Is the soil dry sand, gravel or wet clay?
My observation of red cedar is not all that great either. It will last many years on a wire fence, but not as long on a rail fence. I find that the sapwood will rot rather fast and the heartwood will last forever. The heartwood will support a wire, but when the sapwood rots on a cut post, it isn't pretty.
The natural decay resistance of wood is in the heartwood and not the sapwood (white colored wood).
White oak, including chestnut oak, is naturally decay resistant to a high level.
The arsenic level in playground equipment and the exposure to humans in contact with pressure treated wood has been shown to be lower than the natural amount of arsenic in many soils. This is a political issue and not a science issue. By pressure treating wood we certainly extend the life and thereby reduce the harvest of wood. The issue is complicated and cannot easily be dealt with by a short message in this forum. Much of the "bad" data in Florida has been found to be unsupported by additional studies!
Gene Wengert, forum technical advisor
I just bought a 6x6x18' pressure treated pole for my power pole at the mill site. When I trimmed about an inch at the top on a slope, it was as yellow as if I had just sawn it. The treatment had only gone in about 1/2 inch all the way around. I put a cedar shingle on top to keep the water out and set it into concrete. But Entergy would not let me cut a white oak or a cedar for use. Here white oak is cheap and lasts for years and it does not hurt horses to chew on it. Many barns in this area that were built out of green white oaks are still standing after 50+ years with no treatment for bugs or rot of any kind.
If you buy pressure treated wood, it can be poorly treated (sometimes called "treated to refusal" which usually means little or no penetration of the chemical into the wood and therefore little protection) or it can be properly treated with various chemical retentions (such as 0.4 pounds per cubic foot or 0.6). The wood will be certified for above ground use or for ground contact. Look for the appropriate certification.
Gene Wengert, forum technical advisor
I'd be curious to know where some of you guys are from - around here I never heard of using any hardwoods for fencing or ground-contact use whatsoever - strictly cedar or other softwoods like larch, etc.
Here in western NY all the farmers use cherry, maple, ash, hickory, white oak, or ironwood poles. Very seldom is softwood used, unless it is for a yard fence. Then they usually use larch. We have Japanese larch plantations from prisoners in the 40's. That stands up pretty well. The cherry is usually avoided - it doesn't last as long. With the harsh and varied climate here, it would work anywhere.
I'm in western NC. Black locust is preferred around hear, but red cedar is also used a lot. One lasts about as long as the other, but the cedar is not near as strong. Other hardwoods are used, but locust and cedar is preferred.
I am in north central Arkansas and we just have 2 softwoods and hardwoods as far as the eye can see. SYP will not last unless treated and if you knock the sapwood off the eastern red cedar it will last forever. White oak is by far the best, and plenty of it.
In the early "white" settlement of the East, walnut, American chestnut, white oak, and Osage orange were used for durable fences.
Gene Wengert, forum technical advisor
I guess availability is one factor, eh? I am north of Ottawa, more coniferous than deciduous to choose from here. I talked to a couple of locals about you guys and your hardwood fences and they just shook their heads in disbelief.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor A:
I think the best wood for fencing if you're looking for longevity is osage orane if you are in an area where it grows. It is very, very hard and lasts for many decades - it will outlast the fencing and you probably.
Pressure treated? It depends on the species treated and how well they are treated. It really irks me when people make comments about pressure treated that have absolutely no idea of the nature of the treatment, let alone the human and/or environmental impact. There is none that I am aware of and pressure treated has been around now for a long long time. I just wouldn't make a regular diet of them myself. The splinters will kill you before the pressure treatment.
Comment from contributor B:
I can't believe no one recommended osage orange. It has by far the best rot resistence in eastern Kansas soils of any of the hardwoods mentioned. Eastern red cedar, white oak, and black locust don't even compare. Now if you're talking sawn post, that is a different story as it is hard to find large enough and straight enough osage orange logs to cut into square posts and when you do, most mills won't touch them as they're notorious for having fence staples and other metal embedded in them. However, if you don't mind the rustic, natural look of log post, they are superior to any other post tried in Kansas. They even outlast cement and steel post in most cases. 70 year old posts are no problem in our damp clay soils, but the wood gets so hard you have to pre-drill holes for fasteners once completely dried down.
Comment from contributor C:
I'm not surprised by the diversity of opinions here. I had to learn a lot of this the hard way, when I moved to a farm and had to use what was available for fence. I had two advantages; relatives who'd lived in another state a good ways off; and one very old man as a neighbor who'd grown up in the era of do-it-entirely yourself, with a father and grandfather to teach him.
I'd been told by many to use white oak for fences and pole buildings here in SE Minnesota; "not burr, white". I did, and the stuff rotted off in a few years. Luckily, my old man neighbor was still alive - when I commented on his white oak chicken-coop poles, obviously more than 50 years in the ground, and my fence that was falling down - he was puzzled. It took us a while to figure it out - what he knew, that I didn't, was when to cut.
The internal chemistry of all trees varies hugely with the season. I'd cut mine when I wanted them - the old timers (he said) cut only at "bud break" when they wanted durability. I haven't had the chance to thoroughly check that information; but my next set of white oak fence post is still going fine; 15 years later.
I think some of the disagreement in experience may be due to just this - we've lost the knowledge on when to cut. It makes all the difference - and is quite possibly different for different species; maybe even different regions.
Comment from contributor D:
Pressure treated cedar (red or white) works well. Dip the ends in oil and mound the dirt away from the post. Go a little deeper and backfill it with gravel if you really want them to last.
Comment from contributor E:
In No. Kentucky, our preference has always been black locust. It is important to note that it is black locust and not honey locust which will rot in a year or two. You just need to make sure that the center wood is not starting to rot. If there is no rot, I have seen posts that are still in good shape on this farm that were set before we moved here in 63.
With red cedar (choice #2 in this area) the same rules apply to rot in the center and you need to be sure that there is plenty of red. The white will rot off and the red seems to be indestructible. Osage orange is always the very best, but is in short supply around here. No one considers oak at all around here because of humidity conditions. White oak rots rather quickly in high humidity conditions. The only good for red or black oak is that after drying a year they make pretty good firewood.