The purpose of graveyard dirt, from the Hoodoo tradition, is symbolic of a contract made with the spirit of the one buried*. Basically, the practitioner approaches the grave and asks permission. If permission is granted, a small amount of dirt is exchanged for a silver coin (the reason a Mercury dime is the iconic coin for the gathering of grave dirt). It is believed that, with the prior permission, that the spirit of the buried person has agreed to help with a task. When the graveyard dirt is added to a working, that task is done, and the spirit is no longer bound to the promise.
Regular dirt would just be dirt. It would have no attachment to any specific spirit or purpose, so whom would one ask?
*Typically, the grave should be of a soldier, especially a soldier who died in a battle. However, I have heard of folk practitioners asking permission from people who passed in other ways, or were not military, for purposes somehow related to that person's time on earth or type of death.
What's the poppets purpose? I've made poppets and never needed any type of dirt for them. If you are creating a poppet as a way to end a habit or possibly do harm then graveyard dirt should work. If this is, say, for money, dirt from in front of a bank could work. I would reflect on what the poppet is for and choose the dirt according to that [if it's just a general poppet to represent yourself I would go with dirt from your property]
Agreed, I have made many poppets without the use of dirt in any form. What you include within the poppet is very dependent on what you want to achieve with your working.
In my tradition, graveyard dirt is for spirit work, it is used to include a spirit in your working, for their assistance. Graveyard dirt is also included in workings where you want something to end, come to its conclusion or "die", it's good for cleansing work because of this.
I would personally not use graveyard dirt in a working unless it required these aspects, if you want to use dirt to represent your intention, that can be done. For instance in a healing poppet you could use dirt from a hospital, for money, you would use dirt from a bank, etc. But dirt is not all too often used in poppets, whether you choose to add it, it solely based on your requirements for the working.
