In all sorts of garden-based DIY one of the key jobs that needs to be done again and again is to secure posts into the ground. Whether it’s for fencing, individual items like birdhouses or larger wooden structures like decking or pergolas, having a solid base for the supporting posts is critical.
If it is fencing you’re looking at then treat this article as a companion to our factsheet on Putting Garden Fences Up. That article covers the construction of the fence once the posts have been secured and this article gets those posts in the ground.
Concrete versus post bases or spikes
The two main methods that we’ll cover in this article are concreting posts into a hole in the ground and driving metal holders into the ground to grip the post firmly. There are a variety of different holders, often called by trade names or the generic “post bases” or spikes.
Post bases have the advantage of being relatively easy to use and therefore attractive to DIY novices. Professionals tend to use concrete mixes because they are more versatile and work out cheaper in the long run. We’ll tackle both methods in this article, concrete first.
Digging and drainage
With concrete a hole needs to be dug for the post, about a metre deep or a quarter of the post’s length. It should be three times bigger than the post in both directions. Fill it with gravel first, as this will allow water to drain away.
If you bury the post in a ‘tub’ of concrete, water will collect in the base and rot the post away within a few years. The idea is instead to use the concrete as a sort of collar just to support the post and hold it in position.
Place the post in the hole and drop stones and small chucks of hardcore around the sides. Tamp them down so that the post is held roughly in place, checking that it is roughly upright as you go, until the hole is about half full. If you have quite a few posts to put in it’s best to do all the holes and roughly bed every post in, then mix the concrete apply it to each hole.
Mixing and applying concrete
Refer to our article on Concrete Hints and Tips to find out how to choose and create the right mix. Then pour it into each hole, until it’s slightly proud of the ground level.
Nudge the post back and forth until it is upright, not leaning one way or the other. Then nail a couple battens into the post at forty-five degrees near the base to keep it in place while the concrete sets. Tamp down the concrete to remove air bubbles then take a trowel and smooth the top edge of the concrete, making it slope down from the post to the edge of the hole in all four directions. This will encourage rain water to drain away from the post.
Spikes and post bases
The concrete method is great if you are happy to tackle mixing concrete and it’s very good at tackling all sorts of ground conditions. But the spikes or post bases are easier if you don’t anticipate problems digging the holes. On rocky soil you may have to excavate and use concrete to fill the resulting large and irregular voids, even if you are using post bases.
There are various different makes of post base but the basic method is the same for most of them, they are just sledge-hammered into the ground. They have an open box shape at the top which the fence post drops into, so this needs to be protected while it is hammered into the ground.
Hammering the post base into the ground
Some are supplied with a metal driving tool which fits into the top of the spike to protect it while it is hammered. If not, you can put a short off-cut of post into the spike and hammer that instead. Once the spike has almost disappeared and the bottom of the box is about a centimetre off the ground, the job is done (again that gap is for drainage purposes)
It is vital to ensure that the spike is being driven into the ground square to the line of the fence or other structure, i.e. not twisted. Also you need to check that it is vertical in both planes after every few blows, because once it’s in, it’s very difficult to remove and replace at the correct angle.
Choosing the right method
Whether you use concrete or post bases is largely up to you. If your ground can take it the post bases are quicker, but more expensive for longer runs. And if you get them offline they are very unforgiving. The concrete method is messier and needs confidence with mixing, but you can adjust the angle and lean of the posts to an extent when you first put them in.
In both cases the things you need are easily available from most DIY shops so it really is a case of which one appeals to you more. Just pick whichever method you think will be easier for you.