Q&A for How to Dig Post Holes

Get an excavator. The cave-in protectors that keep people from getting buried alive only are about 8' deep or so. An excavator is both faster and much safer for the depth you're after.

No. You should fill it up to a point just below ground level and cover it with earth. Ideally also make sure the top of the concrete slopes away from the post so water doesn't pool against the wood.

If there's a pole in the hole you won't be able to fit another pole in that hole. Take out the old pole and put a new pole in. And recement.

The frost level is about 16 inches. You will want to go minimum 6 inches below the frost level.

Unless your water table is very high or you hit a water pipe, you shouldn't hit water. Otherwise, you'll have to make a big hole because it'll cave in constantly.

It depends how long you’re going to wait until setting the posts, or if you’re expecting much rain in between then and now. Covering them won’t do a whole lot if you get heavy rain. Your best bet would be to set the posts as soon as possible.

Use a SDS hammer drill with a chisel on it to gradually break up the concrete. You could also just dig the concrete lump out and replace with new concrete when you put the post back.

12' is way too deep. Your posts should be about 2' deep.

A minimum of 4'. This would leave you with 12' above ground. Ideally, it would be 5' or 6' deep, which would leave you with 10-11' respectively.

Between 4 and 5 feet deep for a 4x4 post. And at least 12 inches in diameter.

The concrete is put around the post after the post is placed and usually leveled below the ground surface. When soil is replaced at the end of the job, water sits on the concrete top and rots the post below the ground level, as it is most of the time wet or damp. Raising the concrete above the ground and slopping a gradient away from the post allows water to run off and dry, or use a good water-resistant membrane painted on the post that extends down past the concrete and above the ground height. Protecting the post's bottom with a painted membrane extends its life also, if there is subterranean water seepage through the ground.

Three feet deep should be enough (any less and you risk the post moving with wet soil) with either concrete or tightly packed in dirt/gavel (if you don't use concrete, use a compactor or flat-ended rod or pole to pack the surrounding material in; it is important to get it tightly packed so the post won't move under the constant swinging motion.) That will give you a good nine feet for clearance of the swing. If you want the swing slightly lower, just make the holes a little deeper.

At minimum 25’, better to go 30’ but depends on the load of the post. It is best to use the fast setting cement quickly, this way you ensure it doesn’t set up on you before working it. Adding water for solidity is the tricky part. You’re going to want to go about one cup at a time. Add it in there and watch it for 5 minutes. If it doesn’t turn solid, add another cup and watch another 5 minutes. Continue this until you get your desired outcome.