How deep should fence posts go? You will read a lot of rules about frost lines that do not really apply here. In Snohomish County the depth question is really a water question. Here is the honest version.
How deep fence posts should go
The plain answer is about a third of the post height in the ground. For a six foot fence, that means a post around eight feet long set close to two feet deep, in concrete. That is a starting point, not a law. Soft or wet spots need more. The point is simple. A post needs enough of itself underground, held by concrete, to fight the soil that wants to push it over.
Frost depth is not your real problem
In colder states people dig below the frost line so the ground does not lift the post in winter. Snohomish County rarely freezes deep. Our winters are wet, not hard. So copying a frost-line rule from Minnesota misses the point. Here the enemy is months of soaked, heavy soil from rain that keeps coming from October into May. Depth still matters, but for grip and stability, not for beating a deep freeze.
Concrete versus dirt
This is where cheap fences fail. A post tamped into dirt has nothing solid around it once the ground turns to soup in November. A post set in concrete gets a footing that spreads the load and, done right, sheds water away from the wood. Dirt lets water sit against the post and rot it out. We set posts in concrete, every one, because in this soil dirt-set posts are just future repairs.
Why the cheap bid is cheap
When one quote comes in far below the rest, look at what got left out. The usual cuts are shallow holes, no concrete, and thin posts. It looks the same the day it is done. You find out the difference in the second winter, when the low-bid fence starts to lean and the concrete-set one does not. Paying once beats paying twice. The bag of concrete was never the expensive part.
What good depth looks like on your yard
A good crew checks your actual ground before quoting, because a wet corner near a downspout needs more than a dry rise. They tell you the post length, how deep the holes go, and that the posts get concrete, in writing. If a quote will not say those things, that is your answer. We walk the yard, give a free quote, and put the depth and the concrete right on the page.
Common questions
We dig to depth and set every post in concrete because this ground gives you no cheaper option that lasts. The quote states the post length, the hole depth, and the concrete, so you can hold the finished fence to it.
