A Key for Fence Posts

A neat little trick I learned from two places–a hillbilly and an astute New Zelander–is called “keying a fence post.” It shouldn’t have surprised me really, since this is how a standard T-Post works.

t posts

That little wing on there is a “post key.”

The flat piece of metal on a T-post increases the surface area that resists flexion in the perpendicular axis. The same idea can be applied to a fence post. If you have a terminal fence post (this would not work as well for a corner posts which must resist flexion in perpendicular axes), adding a key can provide substantial bracing WITOUT digging another hole or using another post. It is a very efficient and neat way to improve post performance with only minimal increase in cost.


This key has just been placed. It has not been pounded into the ground. It should be tamped in deeper using the same tamper you use to tamp in the soil around the post to about 3-4 inches below grade. 

I think it is pretty obvious how this works. It is best to dig a groove in the soil with a flat edged spade and the make sure to pound key, which is nothing more than a CCA treated (for ground contact) 2×4 or 2×6 cut to about 16″-24″ long, a few inches below grade so it snugs up against the fence post.

It is best to backfill and tamp the post in to about 8 inches from grade so that when you set the key there is still some room to pound it UP AGAINST the post on the side that the post is gong to be pulled. This works best with square posts (which tamp in better anyway), but will work with round as well. No fasteners are needed.


All this has had is a boot heel press. It can be tamped in another couple inches, and this works better when soil is moist (after a rainfall). Note how it is snugging up against the post.

I was amazed at how much additional rigidity the key adds to the post in that direction. It is very noticeable when you shove on the post in the other three directions where the key provides no support. Of course, making sure to thoroughly set (by tamping) the very bottom of the post at an adequate depth is essential for good performance. The tendency is always to not dig deep enough or tamp long enough or hard enough, and I’ve never met anyone that does either of these adequately the first time. It seems everyone needs to learn the hard way. These posts are only 6 feet long with about 30″ to 32″ below the surface and 40″ to 42″ above the surface–a ratio of about 3:4. Posts should be at least a ratio of 2:3 and preferably 1:1.

With lightweight fencing materials, like polywire, this kind of post termination is more than adequate for even long runs in a permanent installation.  It is also very cost effective, making rotational grazing on even relatively small scales (1-10 acres) worthwhile, and completely answering the accusation that rotational grazing is too expensive. With land prices as they are, its too expensive NOT to enjoy the numerous benefits or rotational grazing for the moderate costs of lightweight and effective electric fencing.


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One Response to A Key for Fence Posts

  1. Pingback: Fencing solutions | A Contrarian's Guide to Grass and Guns

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