A wooden fence post almost always fails in the same place: the band a few inches above and below the soil line, where the wood stays damp longest and air still reaches it. The rest of the fence is usually fine. That means one leaning post rarely calls for a new fence. You can replace a rotted fence post in a day, leave the rails and pickets on either side in place, and reuse most of the hardware.
What you have to decide is how much of the old post and footing to take out. That depends on what has failed and on what the post holds up, so start by checking, then pick a repair route, and work out the concrete before you go to the store.
Step 1: Confirm the Post Is Actually Rotten
Not every leaning post is rotten. A post can tip because its footing was too shallow, because frost heaved it, or because a gate is pulling on it. Each of those needs a different fix, so check before you dig.
- Probe at the soil line. Push a flat screwdriver or an awl into the post right at ground level and a few inches above. Sound wood resists the tip. Rotten wood lets it sink in easily and comes away soft or stringy.
- Dig a few inches down. Pull the soil back from one face of the post and probe again just below grade. This is where decay usually starts, and it can be hidden while the visible part of the post still looks solid.
- Rock the post by hand. If the whole footing moves as one block with the post, the wood may be sound and the footing is the problem. If the post flexes or snaps at the soil line while the concrete stays put, the wood has failed.
- Look at what the post carries. A gate hinge post or a corner post takes far more load than a line post in the middle of a run. If the leaning post holds a gate, read how to brace a sagging fence gate first, because a racked gate can look like a post problem.
If the wood is solid and only the footing has moved, you do not need a new post. Reset the existing one deeper using the depth guidance in how deep a 6-foot fence post should be.
Step 2: Pick the Right Repair Route
Once you know the post is rotten, there are three ways to deal with it. They differ in how long they last, how much digging they take, and which posts they suit.
| Route | What you do | Best for | Main drawback |
|---|---|---|---|
| Repair bracket | Drive a steel post mender into the ground beside the stump and bolt it to the sound part of the post | A line post with rot only at the base and solid wood above | Depends on the above-grade wood staying sound; not suited to gate or corner posts |
| Reset in the same hole | Remove the old post and its footing, then set a new post in the cleaned-out hole | Any post, especially gate, corner and end posts | The most digging, and breaking up an old concrete footing is heavy work |
| Set in the old footing | Cut the post flush, clear the wood stub out of the concrete collar, and set a new post in that opening | An intact, deep footing where the stub can be removed | The concrete collar can trap water against the new post if it does not drain |
Route A: Repair Bracket
A steel post repair bracket (often sold as a post mender or repair spike) is driven into the soil next to the old post, then bolted through the post above the rotted section. It is the fastest fix and leaves the rails untouched. It only works if the post is still solid from a few inches above grade upward, so probe that section first. It is also the weakest of the three routes, so keep it for line posts. A gate post or corner post should be replaced outright.
Route B: Reset in the Same Hole
This is the most durable fix and the one to use for any post that carries a gate or ends a run. You remove the old post and its footing completely, then set a new post the same way you would on a new fence. The steps below cover it in detail.
Route C: Set the New Post in the Old Footing
If the old concrete footing is intact and deep enough, you can cut the post off flush, chisel or drill the rotted stub out of the collar, and set the new post into that opening. It saves breaking out the concrete. The catch is drainage: a sealed concrete cup can hold water against the end grain of the new post. The trade-offs are covered in setting fence posts in dirt vs concrete. If you go this way, make sure the bottom of the opening is not sealed so water can drain out.
Step 3: Replace the Post (Route B Step by Step)
- Call 811 before you dig. Even when you are digging out an existing hole, a new or wider excavation can reach buried lines. See do I need to call 811 before digging fence posts.
- Support the fence. Prop each neighboring panel with a scrap 2x4 screwed to the rails and angled to the ground, so the run does not sag once the post comes free.
- Detach the rails. Back out the screws, or cut through nails between the rail and the post with a reciprocating saw. Keep any brackets that are still in good shape.
- Remove the post and footing. Dig down along one side of the footing to loosen it, then lever or jack it out. If the footing will not come free, break it up in the hole. The fence removal and disposal guide covers pulling footings and getting rid of the concrete.
- Prepare the hole. Clean out loose soil and debris, and add a few inches of gravel at the bottom so water drains away from the end of the post.
- Choose a ground-contact post. A replacement post spends its life in soil, so buy lumber rated for ground contact, not above-ground use. USDA Forest Service guidance notes that AWPA standards specify fence posts be treated to Use Category UC4A, which is the general ground-contact category (USDA Forest Service, Guidelines for selection and use of pressure-treated wood). The rating is printed on the end tag or stamp.
- Set it plumb and in line. Run a string between the posts on either side, set the new post to it, and check plumb on two adjacent faces with a level. Brace it in place.
- Pour and crown the concrete. Fill around the post and slope the top of the concrete away from the wood so rainwater runs off instead of pooling against the post.
- Reattach the rails once the concrete sets. Follow the set time on the bag before you load the post, then remove the temporary props.
Step 4: Work Out the Concrete for the New Post
A replacement post needs a little less concrete than the empty hole suggests, because the post itself takes up some of the volume. Here is a worked example for a 4x4 post (actual size 3.5 by 3.5 inches) in a hole 10 inches across and 24 inches deep:
- Hole volume: 3.1416 x 5 x 5 x 24 = about 1,885 cubic inches, or 1.09 cubic feet.
- Post volume below grade: 3.5 x 3.5 x 24 = 294 cubic inches, or 0.17 cubic feet.
- Concrete needed: 1.09 - 0.17 = about 0.92 cubic feet.
A 60-pound bag yields about 0.45 cubic feet and an 80-pound bag about 0.60 cubic feet, so this post takes three 60-pound bags (0.92 / 0.45 = 2.05, rounded up) or two 80-pound bags (0.92 / 0.60 = 1.53, rounded up). The fence post concrete calculator runs the same math for any hole size and post size, and how many bags of concrete per fence post explains where the yields come from.
If you plan the depth from scratch, the fence post depth calculator gives a starting depth for your fence height.
When One Rotted Post Means More Are Coming
Posts on the same fence were usually installed at the same time, with the same lumber, in the same soil. If one has rotted at the base, probe every post along the run while you have the tools out. Replacing two or three posts in one weekend is less work than coming back for each one separately. If most posts are failing, a repair stops making sense; the fence maintenance guide covers where the line between repair and replacement falls.
Related reading: how to set corner and end posts properly.