Do you need to use concrete for permanent garden fences?
It depends on what you call permanent
Increasing entropy is really the only thing that's permanent.
Although you can't say with certainty how long something will last, you do have the ability to influence longevity. Some sticks shoved into the ground are destined for early failure and steel reinforced 12&quot; diameter x 6' 6000 psi concrete will surely be around after the house is torn down. I'm sure your solution lies somewhere in the middle.
This is decent compromise

http://mielcentral.info
I disagree with image regarding treating the underground lumber. I would still treat it.
Your frost line also has to be taken into consideration.