Fencing
Setting fence posts in blackland clay
How do you set fence posts in clay soil?
Blackland clay swells when wet and shrinks when dry, so it grips a post in winter and lets go in summer. Depth and a properly shaped concrete footing are what keep a fence upright through that cycle.
What the ground is doing
The clay across this part of Texas is expansive. It takes on water and swells, then dries and contracts, and it does that every single year.
A post set in it gets squeezed, lifted, and released on a seasonal cycle. Over enough cycles, a shallow post walks its way loose — which is why fences here lean rather than snap.
Depth is not negotiable
The fix is getting below the zone that does most of the moving, and giving the footing enough mass that seasonal pressure can't lever it.
This is the single most common corner cut in fencing, because it is invisible. Two fences can look identical on install day and be ten years apart in lifespan based only on how deep the holes went.
Shape the top of the footing
Concrete poured flat around a post makes a shelf that holds water against the wood. Crowned so it sheds away, it does the opposite.
Small detail, no extra material, meaningful difference in how long the post stays sound.
Where the ground changes
Go far enough east and the clay gives way to sandier ground that drains faster and grips differently. Neither is harder to build in — they just fail differently if you treat them the same.
That's why posts get set to what the hole actually shows rather than to a number decided in the truck.
The soil moves every year whether you accounted for it or not.