Question
I bought 2x4 eight-foot posts for a grape trellis.  I live in central california.  How deep must these posts go into the ground?  Thank you.

Answer
Hello:

The 2 by 4 pieces are not rated for ground contact. Anchor the posts to piers above ground.

Your frost depth varies from 0 to 6 inches,so depth would not even be an issue as far as frost heave is concerned. You would only have to anchor the piers into the soil.

A single 2 by 4 used as a post will tend to warp. Use a built up (2 pieces connected) or a 4 by 4 post.

The depth of the piers would vary typically between about 1 to 2 feet,depending on the weight of the structure,the nature of the soil and the size of the pier. A shallower and wider pier would function well on a sandy or gravel soil or a well compacted soil with only moderate clay content while a looser organic soil would require a deeper pier. A pier buried to relatively less depth would have to be wider and heavier to compensate for its lack of depth.


Mark Harshman


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