Do you want your pergola to crumble after a heavy storm just because the posts were not structurally built for the weight of a pergola? Look closely at the type of posts you are purchasing with your vinyl pergola. For many cheaper models there is no structural post and relying on a vinyl sleeve may not be sufficient for a large pergola top and canopy.
Many of the light, smaller pergolas only use the vinyl sleeve as the support post. This can be sufficient support for a smaller pergola in an area with very little or no snow. The thickness of the vinyl post sleeve plays a huge part in stability of the pergola. Most pergola companies provide a small bracket that can be mounted onto either wood or concrete deck and then fastened to the vinyl sleeve.
The most common is support post is a wood insert with properly formed spacers allowing the desired vinyl sleeve to fit snugly over the post. Wood supports can either be fastened with a mounting bracket or possibly fastened directly to the frame of a deck or buried 3′ in the ground or concrete. Since the vinyl sleeve protects the wooden post from many natural elements; this method can be an economical choice.
Steel or aluminum post inserts is possibly the better choice when comparing stability and longevity. Steel is stronger than aluminum, but it is good to have a certified coating such as zinc or galvanized to prevent rust on a steel post. This type of post inserts work great in any location, but especially in an area with high winds or close to the beach. I have had numerous comments from homeowners with beach front houses “I don’t want any wood because the moisture and salt causes the wood to rot”.
Since you already chose a quality vinyl pergola that won’t rot, why not choose a quality structural post?