What is the best fence post depth? That depends (of course) on what type of fence you are building and which post you are putting in the ground. We’ll cover a few here with some general fence builder rules.

Privacy Fence Post Depth — 1/3 of Height

The general rule of thumb for privacy fence posts is to bury them 1/3 the depth of the height of the post. This is easy for your typical privacy fence. Use 8′ posts, bury 2′ in the ground, and you’re left with a 6′ post on which to build a fence.

Concrete is still a good idea (I recommend it), especially if you live in an area with high winds or occasional hurricanes. I’ve even drilled a 9/16″ x 8″ hole in the bottoms of the posts and driven a piece of re-bar in with about 12″ sticking out. The result is a post buried 2 feet in the ground, with re-bar another 12″ (driven into the clay soil), surrounded by concrete — very strong posts. Overkill? Whatever, dude.

Farm & Ranch Fence

Your typical farm or ranch fence, especially one with wire stretched, has 2 types of posts — line posts and corner posts.

Use the 1/3 of height rule for the line posts depths. With 6 foot posts, you will probably bury 1.5 to 2 feet and end up with a 4 to 4.5 foot post. For corner posts, you might want to use a rule of 1/2 the height for the fence post depth. So, a 5 foot tall corner post would probably be buried 2.5 feet in the ground — probably more like 3 feet buried of an 8′ post.

Here are some options for those of you perplexed by the question of how to preserve wood posts. Whether you are trying to build a long-lasting fence or other structure or trying to extend the life of existing wood posts you have options. Without exceptions, the options are far easier before installation.

Pressure Treated Wood Posts
No additional work required – just buy wood posts treated for ground contact (usually .40pcf). Depending on the area where you are installing your pressure treated wood posts, they should last between 10 and 30 years (maybe more). 10 years if the area is pretty wet and/or has a bad termite problem and 30 years if the area is pretty dry.

Poly Coated Treated Wood Posts
I only know of one place that offers poly coated wood posts – American Pole and Timber based in Houston, TX. The coating is a UV-resistant “poly urea” coating (look and feels like heavy vinyl) and is obviously tough as hell and will not come off of the wood. They guarantee treated poly coated posts will last 50 years. Pretty impressive. The product has only been around for about 10 years but I would put money on 50 years for treated wood coated with a thick UV-resistant vinyl. They supply any quantity but if you are outside of Texas or Louisiana, you might need to buy quite a few to justify the freight expense. You only need to have the post coated from about 6 inches above the ground line to the bottom of the post.

Plastic Coated Wood Posts
Similar to poly coated wood but I wouldn’t put my money on it. Buy treated posts and spray the bottom of the post up to about 6 inches above the ground line with spray-on plastic in a can. You can get a can of spray-on plastic for about $5 at the major big-box hardware stores. One can should easily cover the bottom 3 feet of about 10 posts. It’s cheaper than the vinyl option and should add 10 years onto any posts life.

Sealants or Stains
If you are going to seal or stain pressure treated wood, make sure it is dry first since sealing in the moisture left from the treating process will only make your posts rot faster. Sealing untreated posts will add a few years to their lives but, seriously, just get treated posts – unless you just LIKE replacing fences.

Paint
Paint is for color – not protection. Yes, it protects a little but, again, if you are going to use paint to preserve untreated wood posts just go ahead and admit that you like replacing fence posts. Want color? Paint away. Want preservation? Use treated posts.

The BEST WAY to Preserve Wood Posts
In my opinion, the absolute BEST way to preserve wood posts is with pressure treatment – whichever treatment chemical you choose – and a coating of some kind. The longest lasting wood posts will be pressure treated and coated with the vinyl coating. The most bang for your buck will probably be to use pressure treated posts and spray-on plastic.

Now you know how to preserve wood posts and which methods will work best for you. If you choose paint, don’t call me because I hate replacing posts. I will gladly lay in my hammock – supported by my vinyl coated treated posts – while you install your second set of painted posts, though.