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Setting fence posts into chalk subsoil?

 
pollinator
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Hi folks,

The last few days I have ended up messing around with fence posts. Our "soil" is nice and loamy, but about 8 inches down you hit chalk subsoil.  I need to put some sturdy posts in for some fencing and some plant supports. Previously the posts we have put in have been set in concrete, but this time I am trying my hand at setting them in earth without the concrete. I have a heavy steel digging bar with pretty good blade like end. It can smash the chalk up pretty easily, and but through most of the flints.  The subsoil is pretty much soil packed chalk down for a few hundred meters.

Anyway,  my question:

How wide should I be digging the holes? My instinct tells me that I should be digging narrow holes as tight to the post as possible. The trouble is when I come to pack the dirt back in I can't ram it very effectively because there is not really adequate space for the bar. Elsewhere, I have read conflicting comments that suggest I should be digging a hole 3 times the diameter of the post. This seems very counter intuitive as it would surely just weaken the soil structure and make the post less stable?
 
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Michael Cox wrote:Hi folks,

The last few days I have ended up messing around with fence posts. Our "soil" is nice and loamy, but about 8 inches down you hit chalk subsoil.  I need to put some sturdy posts in for some fencing and some plant supports. Previously the posts we have put in have been set in concrete, but this time I am trying my hand at setting them in earth without the concrete. I have a heavy steel digging bar with pretty good blade like end. It can smash the chalk up pretty easily, and but through most of the flints.  The subsoil is pretty much soil packed chalk down for a few hundred meters.

Anyway,  my question:

How wide should I be digging the holes? My instinct tells me that I should be digging narrow holes as tight to the post as possible. The trouble is when I come to pack the dirt back in I can't ram it very effectively because there is not really adequate space for the bar. Elsewhere, I have read conflicting comments that suggest I should be digging a hole 3 times the diameter of the post. This seems very counter intuitive as it would surely just weaken the soil structure and make the post less stable?



First, to be clear, I am NOT a soil or post-hole expert. This is just my 2-cents worth based on a similar problem we've had here in our very rocky (limestone) landscape. Over our property, 2 feet of usable soil seems like a luxury. Most of the time it's 2 to 12 inches deep and then you hit rock. We've found that there are essentially three ways to get around this problem. 1 -- Pound in a metal T-post instead of a wooden one. Those things can easily crush through soft rock (chalk would be a breeze) and use a minimal hole (so no wobbling). 2 -- Dig and pick a hole deep enough for your purpose but as small as possible, then backfill with rocks, not soil, jammed down against the post as tightly as you can get them. (A sledgehammer works well to really pound them in and if they break, no problem, just keep pounding until every available space is filled in). 3 -- forget posts and put your fence ON the ground instead of in it. A zig-zag or rail fence is a good example, but you can also use tripod-style posts to hold your rails or wire. Lots of old-timey fences made that way are still standing after hundreds of years. I know because we have an old zig-zag fence on our property that was put here in the 1800s.

Anyway, I hope that helps. Good luck!
 
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