Fence posts fail at the ground line, where wood meets wet soil. The post rots, the fence leans, and the panels follow — but the panels and rails are usually fine. Replacing one post is a half-day job with a shovel, a level, and a bag of concrete or gravel, and it beats rebuilding a fence that has years of life left. If the whole fence is leaning, start with the leaning fence guide to find which posts are actually bad.
Wood rots where it stays wet, and the soil line is wet most of the year. A post set in concrete can rot faster, not slower: the concrete collar holds water against the wood like a cup. Frost heave lifts shallow posts, and wind works the loose ones until the hole widens. Pressure-treated wood and drainage are what make a post last 15–20 years instead of five. When you probe a suspect post with a screwdriver at the ground line and it sinks in soft, the post is done — no amount of straightening will save it.
Check what else is sound. Push the post and look at the rails and panels attached to it. If the rails are solid and the panels are straight, replace just the post. If the rails are rotted too, plan to replace that section of rail as well. One bad post is a repair; three bad posts in a row is a rebuild.
Take the panels and rails off. Unscrew or pry off the panels and rails attached to the post, and set them aside in order. Label which side faces out — it saves confusion when they go back. A helper makes this far easier, since a full panel is awkward alone.
Pull the old post out. Rock it back and forth to loosen it, then lift. If it is set in concrete, dig around the footing and lift post and concrete together — a car jack under a chained 2x4 gives the leverage. If the footing will not move, break it with a sledgehammer and take it out in pieces. Wear gloves and eye protection: old concrete and splintered wood are unforgiving.
Clean and deepen the hole. Clear the old concrete and loose soil. The hole should hold about a third of the post underground, and deeper than the frost line where winters freeze. A post-hole digger or a narrow shovel does the work; keep the hole no wider than it needs to be, or the post will wobble in loose fill.
Set the new post plumb and brace it. Use a pressure-treated post rated for ground contact. Put four to six inches of gravel in the bottom for drainage, set the post, and check plumb on two sides with a level. Brace it with two 2x4s staked to the ground so it cannot move while the fill sets.
Backfill with gravel or concrete. Pack gravel in layers, tamping each one, or pour fast-setting concrete mixed to the bag directions and slope the top away from the post so water runs off. Gravel drains and makes the next replacement easy; concrete holds firmer for gate posts and windy spots. Either way, keep the fill a couple of inches below grade and finish with soil.
Rehang after the cure. Concrete needs 24–48 hours before you load it with panels; gravel is ready the same day, but recheck plumb before you reattach. Put the rails and panels back in their original order, check the gate still latches — a post that moved even a little can throw a gate off, and the sagging gate guide covers the fix if it does — and fill the last of the soil around the base.
Concrete is stronger and best for gate posts, corner posts, and windy sites. Gravel drains, which is what keeps the post from rotting at the soil line, and it makes the next replacement a dig instead of a demolition. In a wet climate, gravel wins for ordinary line posts. For a gate post that carries weight and swinging force, concrete wins. There is no wrong answer for a single post — there is only the wrong answer for your soil and your gate.
About a third of the post underground, and below the frost line where winters freeze — typically 24–36 inches for a six-foot fence. A shallow post heaves in winter and leans by spring.
Yes — tamped gravel works well for line posts and drains better than concrete, which helps the post last longer. Use concrete for gate posts and corners, where the load and leverage are higher.
Fast-setting concrete firms up in about an hour, but wait 24–48 hours before hanging panels on the post. Loading it early can shift the post out of plumb while the concrete is still green.
Yes, and rated for ground contact — the label should say so. Untreated wood in soil rots in a few years. Seal the cut ends too, since the treatment does not reach the middle of the board.