Fence post spacing in addition to using root resistant materials, there are several important considerations when installing a wooden gate post. The post must be solitary and buried deep enough to withstand the lateral pressure of the hanging gate. The bottom of the post must be buried deep enough to keep the post from moving, caused by frost lift. Drainage must be provided to prevent rot at the base of the post. When installing a gate post, typically at least 1/3 of the total length of the post is buried in the ground.
Contact your local building codes control office to determine the recommended minimum depth to bury the gate post.