Ensure your posts are level in the holes before pouring concrete or other material. You can temporarily fix the post in position with wood scraps, or even use a second person to ensure that the post does not move while pouring the concrete. If using concrete, keep in mind that drying times can vary depending on the type of concrete you use to set your posts (from as little as 30 minutes to as much as 24 hours).

Do I need to use concrete?

No, concrete is the go-to product as it is strong and durable. There are alternative products such as foam that can reduce labor and handling costs. It is highly recommended that you do not set posts directly in soil for 2 reasons: stability and rot. The increased surface area provided by concrete or foam reduces the amount of PSI that is transferred to the soil, providing a more stable post. Wood is never to be in direct contact with dirt. A post exposed directly to soil can rot out in a matter of a few years, causing you to replace your fence prematurely. Posts should be wrapped with post wrap to help block moisture from contacting the wood below grade.

Do I fill the hole to the top with concrete?

Leave at least 6 inches of hole when pouring concrete so soil can be put on top. This acts as another layer to prevent heaving from frost.
The amount of concrete depends on the volume of the hole and the size of the post. The amount needed is the volume of the hole minus the volume of the post. The hole or tube should be at least 4” bigger than the post. So, a 4×4 post should have an 8” hole or tube at minimum.

How to Install a Fence Post