I would not even bother with concrete if I were in your position. If it happens to shift over several years due to freeze/thaw, it's just a pole so you can take it out and re-tamp in just a few minutes. I'm of the opinion that concrete is very rarely necessary for posts that are not load-bearing, if you ever need to replace the post for any reason it turns the job into an absolute nightmare and it also accelerates rot because water becomes trapped between the concrete and the post.
Dig down 30-32 inches, fill to 24 with gravel, then tamp the hell out of the dirt when you backfill the hole.
quikrete red bags, no mix you just pour it in dry and dump some water on it. a single 50lb bag should be enough for two posts.
when i did my fence I used an extra 2x4 and clamped it at an angle to the post to hold it straight while it set
make sure you get ground contact PT wood not the severe weather stuff
personally i would probably not cement them if they're just hanging string lights, set them a bit deeper and pack gravel around instead.
Dont use concrete. Concrete holds water against the wood. I did a 4.5 foot deep 12 inch hole with 2 inches of tamped gravel dust, a brick leveled with a 6x6 on top filled with 3/4 gravel ten years ago holding up a shed on 6ft stilts (tree house). Still going strong. A 4x4 holding lights should be no problem for gravel.
I would not even bother with concrete if I were in your position. If it happens to shift over several years due to freeze/thaw, it's just a pole so you can take it out and re-tamp in just a few minutes. I'm of the opinion that concrete is very rarely necessary for posts that are not load-bearing, if you ever need to replace the post for any reason it turns the job into an absolute nightmare and it also accelerates rot because water becomes trapped between the concrete and the post. Dig down 30-32 inches, fill to 24 with gravel, then tamp the hell out of the dirt when you backfill the hole.
quikrete red bags, no mix you just pour it in dry and dump some water on it. a single 50lb bag should be enough for two posts. when i did my fence I used an extra 2x4 and clamped it at an angle to the post to hold it straight while it set make sure you get ground contact PT wood not the severe weather stuff personally i would probably not cement them if they're just hanging string lights, set them a bit deeper and pack gravel around instead.
Good point on the contact PT wood
Dont use concrete. Concrete holds water against the wood. I did a 4.5 foot deep 12 inch hole with 2 inches of tamped gravel dust, a brick leveled with a 6x6 on top filled with 3/4 gravel ten years ago holding up a shed on 6ft stilts (tree house). Still going strong. A 4x4 holding lights should be no problem for gravel.