Why Fence Posts Rot (and How to Prevent It)

Prevention

1. Ground-contact rated posts
2. Proper depth
3. Concrete crowns
4. Clear soil and mulch from posts
5. Redirect sprinklers and downspouts

Related: Post depth in red clay.

Where rot starts

The few inches just above and below the soil line are the danger zone. Below, the soil has little oxygen; above, wood dries out. At the surface, wood stays damp and gets plenty of air, which is exactly what decay fungi need. Charlotte’s dense red clay holds water against posts after every rain, so this zone stays wet longer than in sandy soils.

Above-ground vs. ground-contact

Treated lumber is labeled for its intended use. Above-ground lumber has less preservative and isn’t meant to be buried. Ground-contact lumber is treated for soil contact. Posts should always be ground-contact rated; pickets and rails above ground can be above-ground rated.

Habits that shorten post life

• Mulch, soil or pine straw piled against posts
• Sprinklers hitting the same posts daily
• Downspouts draining along the fence line
• Concrete left flat or cupped so it holds water

Inspect yearly

Push on each post and probe at grade with a screwdriver. Soft wood means it’s time to plan a repair.