There are lots of types of dirt, and knowing whether or not you can set fence posts in the dirt is important for the life-span of the fence. Setting a fence post in dirt can seem like a daunting task but have no fear.
You can set fence posts in dirt, but it does require some knowledge and preparation. The lifespan of a fence post is directly related to the composition of the soil and the type of post that is used. There are some techniques to know that will expand the life of the post set in dirt.
In this article we will go over the different techniques that will help guide you in the process of putting your fence posts in the ground.
Putting Fence Posts In Dirt
Fence posts are the supports of your fence. Properly setting them will determine a large part of your fence’s lifespan. This means that using proper tools and techniques is paramount to longevity. Take heart though, it is a simple process and very hard to mess up.
- Dig a hole about 2 inches greater in diameter than your post.
- Put your post in the hole.
- Fill the hole with about 1 inch of dirt.
- Tamp the dirt down to compact it.
- Repeat this until you fill the hole up.
This will be the same idea for all variants. With this in mind, let’s talk about setting your post in the dirt.
The tools you will need to set your post in dirt properly will depend on the dirt you have. If you are using only dirt then all you need is a shovel and tamping tool.
A tamping tool could be anything from scrap wood to a metal rod with a flat head. The longer the better. It will make it easier to compact the ground if you don’t have to bend over to tamp the ground.
If you find that setting your post in just dirt makes you nervous then you will also need concrete and something to mix it in. Not to mention something to mix it with. This could be an old shovel, garden trowel, or long stick.
In the past, I’ve used old wheelbarrows, five-gallon buckets, and old shovels.
The type of dirt you are setting your post will make all the difference. Some soils are great for compacting while others are great for digging. So here are some basics.
Soft soils will include sand, silt, loam, and mildly chalky soils.
Sandy soils are excellent for digging and tamping. The big issues here are compacting it properly and preventing your hole from filling in as you dig. To properly compact, take extra care while tamping and spend extra time and energy doing so. To keep your hole from filling in you need to either get it a little wet or dig an extra-wide hole.
Sandy soils drain very well so losing integrity from water saturation is not likely. This does make rot slower, however, it does not solve the problem.
Silty soils are a lot like sandy soils. The big differences are that silt doesn’t drain well and retain some give as you compact. It will lose the compaction and will increase the speed your posts rot if it gets saturated.
This means you would want to consider either increasing the area of your hole or use something to reinforce. We cover those in the Common Practices section of this page.
Loam has similar amounts of sand, silt, and clay. So expect some in-betweens when working with it. Because of this, you will need to consider the same ideas as with silt.
Chalky soils are great when working with a mild mixture of chalk, but a lot like clay when using a more concentrated mixture. It will provide great support for your post and drains well.
The hard soils will include gravel, gravel in soil, and clay.
Gravel, though not technically dirt, is great for setting posts. It requires the post to be buried more than normal. A little more than 1/3 of the post should be underground. It provides excellent support and drainage.
You probably won’t be digging in just gravel. However, if you are then you are brave than most.
Gravel in the soil is terrible when digging your hole. You will hit rocks every scoop. However, it aids in drainage and will provide great support for your fence.
Clay is another one you probably won’t be digging in. The higher the clay concentration the more like solid rock it will be to dig through. If you can support the fence steadily as the clay grows and sinks, then it does provide excellent support.
If dirt is high in clay it will not drain very well and this will increase the rate of your posts rotting if they are wooden.
The Importance Of Wood
Setting your post in dirt requires good wood unless you want to replace the posts every couple of years. Below is a picture of why you need to choose and protect your wood.
What you see happening to the base of these posts is called wood rot.
If your dirt doesn’t drain well then you will need to protect your wood from rot. There are of couple ways to prevent your wood from rotting, which we will discuss in detail for the next section.
This is why it is imperative to know the type of soil you have. Protecting your wood is a step you might not even need to consider if your soil drains well as it is.
Protecting your wood will increase the life and strength of your fence. Take extra heed to maintain it and your fence will last a long time.
Techniques To Prevent Rot
To prevent wood rotting your set posts in the dirt you can do a few things. Use a wood preserver, increase the drainage of your soil, and buy heartwood.
Wood preservatives are abundant and can even be found already in your house. These might raise your eyebrow. The most common preservatives include used engine oil, tar, and copper naphthenate.
These will all increase the life of your posts for a very long time.
Using oil will help repel water and bugs. We have discussed using oil on wood in length in our popular article Can You Paint a Fence with Engine Oil which has some surprising facts in it you may not have known about painting your fence with oil.
Putting tar on wood has a similar effect that using oil does. There really isn’t much difference when setting your post.
Copper naphthenate is the most accepted current practice. It provides the same effects as oil and tar and is currently considered environmentally friendly. It is a little pricey though. Not awful, just worth saying. Home Depot prices a five-gallon bucket at around $87.55.
How far that bucket goes depends on how many coats and how big your posts are. So it may be worth it for setting in the dirt.
When coating your posts make sure not to coat the bottom face of the post. If you do this it will prevent proper water circulation after the post is set.
Increasing your drainage is pretty easy. All you do is place gravel at the bottom of your dirt hole before you set your post. This allows easy water drainage without hurting the integrity of your hole and post.
Buying heartwood is a good idea too. Heartwood is the wood the comes from the center of the tree. It is generally a darker color than sapwood (the wood is not heartwood). Heartwood is more rot and pest resistant than sapwood.
Here is an example of partial heartwood. The dark sections are heartwood.
The important thing is to prevent rot. Rot generally occurs at and just below ground level. So those are the areas that need to be protected the most.
Even though you can set a post in the dirt, I don’t recommend it unless you are using sandy dirt or dirt full of gravel. Otherwise, the dirt just has too much give.
Setting in the dirt for a support post that does not carry a heavy load-bearing post is also okay. Ranchers will do this often with wood rail fences.
Most of us will need a fence that can withstand heavy winds and rains though. Most of us will be setting our posts in the dirt that is not ideal for integrity. With that in mind, a common practice for setting posts is to do as follows.
- After you dig your post hole, fill the bottom with gravel (Keep in mind this makes your hole more shallow. A good rule of thumb is to assume one-third of your post should be submerged under the top of the ground for proper support.)
- Make sure your post is level with the others
- Set your post the way you want it
- Pour concrete into the hole and let it cure
- After the concrete is cured caulk any seams in the concrete and the seam between the wood and concrete.
Setting your post like this will ensure both strength and longevity.
Whether you set your post in just dirt or decide to use concrete to help steady it, you have to ensure:
- Proper drainage
- Prevention of rot
- Proper securing (compacting if dirt, curing if concrete)
These three things are the most important rules for building a fence. If any one of these three is neglected then the life of your fence will be greatly decreased.
So if you set your post in dirt make sure it compacts well and drains well. Otherwise, you will have to make modifications to the dirt and post.