Why Gate Posts Fail (and It's Rarely the Gate's Fault)

A garden gate looks simple, but it puts surprising force on its posts. Every time it swings, the weight of the gate acts like a lever, multiplying the load at ground level. Add wind catching a solid panel, children swinging on it, or a heavy vehicle brushing past, and a poorly set post will soon shift. The result is a gate that drops, drags, or refuses to latch. Most failures trace back to two things: not enough depth below ground, and not enough concrete around the post. A gate post is a foundation, not just a fence post. Treat it that way, and it will stay put for decades.

Choosing the Right Post for the Job

Start with the post itself. For a typical pedestrian garden gate up to 1 metre wide, a treated timber post of at least 100mm x 100mm is the minimum. For wider gates, heavier designs, or anything near a driveway, go to 125mm x 125mm or 150mm x 150mm. Concrete posts are excellent where rot is a concern, and metal posts suit modern styles, but both need the same careful setting. The post must be strong enough to resist bending, not just vertical load. A spindly post in soft ground will flex no matter how much concrete you pour around it.

Consider your soil, too. Clay holds well but can shrink and swell, sandy soil drains quickly but offers less grip, and chalk or gravel can be unstable. In loose or wet ground, choose a larger post and dig deeper. If the gate is automated or very heavy, ask a structural engineer for advice before you dig.

How Deep Should a Gate Post Go?

Depth is where most DIY installations fall short. A fence post might be fine at 600mm, but a gate post should go deeper. As a rule of thumb, aim for at least one-third of the post's total length below ground, and never less than 600mm. For a heavy gate, a wide gate, or exposed site, 750mm to 900mm is sensible. The hole should be about three times the width of the post. Bell out the bottom slightly so the concrete forms a wider plug that resists lifting. Before you dig, check for buried services. Pipes, cables, and drainage runs are easy to miss and expensive to hit.

• Light pedestrian gate: 600mm deep, 100mm post
• Standard garden gate: 750mm deep, 100mm to 125mm post
• Heavy or wide gate: 900mm deep, 125mm to 150mm post
• Driveway or automated gate: 900mm+ and professional advice

Setting the Post: A Practical Sequence

Dig the hole to depth, then put 100mm of hardcore or gravel in the bottom. This gives water somewhere to drain and stops the post sitting in wet soil. Stand the post on the hardcore, not on loose earth. Check the height: allow for the gate clearance above ground and the hinge positions. Brace the post with two or three timber stakes driven into the ground and clamped or screwed to the post. These braces hold everything steady while the concrete sets.

Mix your concrete. A standard mix is one part cement to four parts ballast, or use a rapid-setting concrete for speed. Pour it in stages, tamping with a piece of timber to remove air pockets. Fill the hole to just above ground level, then slope the top away from the post so water runs off. This crown is important. A flat or hollow top will pool water and rot a timber post at its most vulnerable point.

Check Alignment Before the Concrete Sets

This is the step that saves you from future misery. Once concrete begins to cure, moving the post becomes a demolition job. Before it sets, check the post is plumb using a spirit level on two adjacent faces. Then check the gate opening. Use a string line between the hinge post and the latch post. Measure the gap at the top and bottom: it should be consistent. If one post leans in or out, the gate will bind or swing open on its own.

If you can, hang the gate temporarily on its hinges while the concrete is still soft. Open and close it. Watch for dragging, catching, or a gap that changes. Check that the latch post is at the same height and parallel. For double gates, check the centre meeting point. Adjust the braces until everything is right. Only then leave the concrete alone. Rapid-setting concrete may go off in 15 to 30 minutes, so have your checks planned before you mix. Standard concrete needs 24 to 48 hours before you hang the gate properly.

Finishing, Curing and Long-Term Care

After the concrete has cured, remove the braces and backfill around the post with soil, firming it gently. For timber, treat any cut ends with preservative. Hang the gate and check the swing again. A small adjustment to hinges is normal; a post that has moved is not. Keep the base clear of soil and mulch so water does not sit against the post. Once a year, check for movement, cracks in the concrete, or rust on metal posts. Tighten hinges and oil latches. If a post does start to lean, dig it out and reset it properly rather than trying to force it back. A gate post set deep, braced well, and checked before the concrete sets will give you decades of smooth, reliable outdoor access.