A vinyl fence is really only as strong as its posts. That is, no matter how solid your fence is built, it won't be level or sturdy if the posts are not firmly set into the ground. Obviously, when you are setting posts directly into soil, it can be a little unpredictable. This is why there are no set rules for how deep and wide holes need to be for fence posts. This is also affected by whether or not you are going to set your posts into concrete footings.
This article should help you determine whether your fence posts can be sent directly into the soil, or whether you will need to use concrete footings for them.
Can Your Dig Deep Enough
The biggest factor is really how deep you are able to dig into your soil. If you don't use concrete footing, you need to dig deeper into your soil. But, it also depends on how big and heavy your fence is going to be. If you are going to install a 10' tall metal fence, you will need to have very deep posts. But, if you're just installing a 4' tall wooden picket fence, you will probably be able to easily dig just a few feet into the soil.
Another important factor is how many posts you're going to have. If your post are spaced further away, then you will need to have they will need to be stronger to support the added weight of each panel. So, if you aren't able to dig deep into your soil because it is rocky and or full of tree roots, you may need to place your posts closer together.
Concrete footing only becomes necessary when you are installing tall fences that are heavy, with posts that are further apart, and when you cannot dig very deep into the soil.
Testing Your Soil
Ultimately, you have to use your best judgment, and you often have to begin digging into your soil before you can even make any purchases or major decisions. That is, you can try to dig your fence post to determine how difficult it is going to be to create the holes. If it seems like there are no problems, then you might be able to design your fence so that it doesn't need concrete footing. Obviously, this also speeds up the process and makes it more affordable.
There is really no wrong or right way to build a fence; it just really depends on the style of your fence, and the consistency of your soil. Learn more about fencing by contacting services such as Canyon Fence Co.