how to place 4x4 posts in ground in michigan?

I have couple of different situations where I need to put 4x4 posts in ground in Michigan...
first project is raised garden, using 2x10's with 4x4 posts every 6'. I was planning to cement the 2' 4x4 posts about 1' into ground. A friend told me frost would push them up and he said I should just use crushed rock for this project. What is best way?
second project is rebuilding poorly constructed gates. I was told to dig holes at least 42" deep, then cement 4x4 posts in place. Is it necessary to go so deep? TIA.
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On Jun 15, 11:43 am, snipped-for-privacy@home.com wrote:

The rule of thumb is to go below the frost line -- that is around here. michigan might be different though.
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On Jun 15, 10:43 am, snipped-for-privacy@home.com wrote:

The conventional wisdom, which I see no reason to doubt in this case, is that you have to go below the frost line. If you don't, freezing ground and/or water that seeps in and pools under the post will push it up. So I have always sunk posts about 40" deep in Chicago area. It's been working for me. I have noticed that the professional fence installers do the same thing. Crushed rock seems to work fine for filling around the posts for fencing, but for the gate you might want concrete for added mass. Drive a few stout nails partway into the buried part of the post to connect it to the concrete. -- H
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On Jun 15, 11:43 am, snipped-for-privacy@home.com wrote:

I'm in MI and have put in a number of posts recently, I'll agree with the 40 inches or so, use a tape, 40 inches is deeper than it looks, especially when your doing it by hand. I've put the post in place and set it for level, then poured dry redimix into the hole almost to top and run a garden hose on it for a few minutes. Let the water puddle on the top for a few minutes, and stick a narrow dowel into the concrete to make sure the water gets all the way around. check for level again, and by the next day its done.
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On Mon, 15 Jun 2009 15:43:53 GMT, snipped-for-privacy@home.com wrote:

I'd say let it float. We did one for my dad that way a few years ago. 4x8' & 2feet high. we used cedar 1x12s for the sides & 4x4's in the corners. Nailed with galvanized ring-shanked nails. Put one stretcher in the center. Looks fine after 3 NY winters.

Hard to say without knowing what the gates are and what is 'poorly constructed' about them. A 10' driveway gate that weighs 400 pounds will need a lot more support than an aluminum garden gate that weighs 5.
But if I was just trying to keep a 4x4 plumb in this part of the world I'd go 48 because that's what the frost level is here. Then I'd backfill a bit with #2 crushed stone- then a bag of post hole cement.
Jim
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snipped-for-privacy@home.com wrote in

One foot down doesn't seem like enough. I helped my husband dig post holes. I remember making them 3 feet deep. I can't ask him, since he's since passed on. But it was for a 6 foot high stockade fence.
We're near Niagara Falls in NY. Lots of freezing here with long winters from Oct/Nov thru April/May.
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I'd definlitely say..... vertically!
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