Use Wood Glue
When using pocket holes to make edge joints I would recommend using a quality wood glue in addition to the pocket screws. Even though pocket hole joints don’t require it, in my opinion, adding glue to a pocket hole joint improves the quality of the joint.
When a pocket screw is screwed through the angled pocket hole it draws the two pieces of wood tightly together. This creates a strong joint, but it doesn’t take into account the wood itself.
Wood is always moving due to seasonal changes. Wood is constantly absorbing and releasing moisture, just as it would when it was alive.When the drinking straws, ummm wood fibers, absorb moisture the wood swells and gets bigger. When it releases moisture the wood shrinks and gets smaller. If you build a project when it’s humid, you may notice when the air is drier that some of the joints don’t fit together as well as when it was more humid.
I’ve noticed this joint issue when edge joining table tops for furniture projects. I built my air conditioner dresser in the summer when it was humid, but I didn’t edge glue the top pieces. The top looked great in the summer, but in the cooler months, the joints of the top just ever so slightly pulled away from each other. And the edge of one of the pieces even started to slightly curl up.
Can you stop wood movement? The short answer is no, but you can help reduce some of these issues by gluing the joints. If I glued the top of the air conditioner dresser it wouldn’t be moving like it does.
Pocket holes create a strong, lasting joint, but in my opinion that joint is made even better by adding a quality wood glue.