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So spring has arrived, and we have decided to build a 20' x 40' enclosed area in which to place a garden (we have many deer, rabbits and other garden veggie thieves in the area).

The plan is to build a 5' tall fence, using 4x4 cedar for the posts. The posts would be set ~3' into the ground. We are in an area with a pretty active freeze/thaw cycle (Minnesota). The fence panels themselves would be framed metal garden mesh (i.e.- a doubled up 1x4 "frame" with heavy duty wire mesh typically used for horse fences in the center). This should greatly reduce the wind load on the fence, as there will be little surface area.

I went and calculated the amount of quikrete I'd need to set the posts in, and it came to nearly $40/post (5 50lb bags per post). With 14 posts, this ends up being $580 just for the concrete for the fence! After doing some reading, it appears that some fence builders will use 3" of pea gravel as a base under the post, then fill around the post to about 1' below the surface with compacted pea gravel, then do 8" of concrete, topped with 4" of soil. For a garden fence that will have relatively small lateral loads, does this seem to be an appropriate way to do things? Any thoughts on how I should set these posts?

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Pea gravel for the base of the hole makes sense...for drainage. On the sides, less so. I'd opt for crushed rock which will compact better when tamping. If tamped properly, you likely don't even need concrete.

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  • It's not as much fun without the concrete ;)
    – uncle brad
    May 6, 2011 at 19:00
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Its the pier size that matters more than the depth.2'in the ground is sufficient, unless there are serious compaction issues. Dig a 12" wide 2'deep hole. Use a post collar to protect the base or crown the concrete. You will only need 135 lbs of concrete and with that still have enough to crown or slope the top. Thats a 90lb pound sack and a half. If you need an accelerator use whats called quick rock. It will cost you about $5.00 per post. The concrete is under $3.00 for a 90lb sack. 3' in the ground is over-kill. I have been hearing this for years and have built miles of fences that I have to warranty.

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The Post Collar

The Post Collar

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I recently set some posts, but not quite a deeply as you're planning. Using an ordinary post hole digger to dig the hole, I still used a little less than an 80 lb. bag per post. How wide is the hole you're planning on digging?

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  • I was going off of the post-hole calculator on the quikrete site. For a 4x4 post set 3' deep, it is suggested (both on their site, and elsewhere) to use a 12" diameter hole. Taking out the post space, this leaves ~2.2 cu feet. A 50lb bag of quikrete yields about a half a cubic foot, so 5 bags is about right.. :/
    – MarkD
    May 6, 2011 at 19:59
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    Could it be that the quikrete calculator is designed to sell quikrete? For a cedar post I'm leaning towards DA01's suggestion of crushed rock.
    – uncle brad
    May 9, 2011 at 22:11
  • For a fence I recently built, I set 4"x4"x8' posts 3' into the ground (actually I dug down 3.5' and put .5' of gravel at the bottom). The holes were 12" diameter and I used about 2.5 90-lb bags of Quikrete for each hole, so it came to about $10/hole for concrete.
    – Sam
    Aug 14, 2011 at 22:39

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