Pressure Treated wood is used for a wide variety of garden structures, be it a shed, a playhouse, fencing, decking or picnic tables, through to telephone poles, seaside piers and, believe it or not, can also be used for residential building foundations in some countries! Its unique ability to fend off decay makes it ideal in any high moisture and/or ground contact installations means that pressure-treated wood is truly a "wood for all seasons"... a rugged exterior building product that's rot and insect resistant, which, with the right maintenance can last for years and years.......
There is so much misinformation and even disinformation concerning pressure-treated wood and its maintenance requirements.
So, the question is...... If Pressure treated wood is so tough, why bother coating in further preservative? Although the infused preservative prevents rot, it does not inhibit weathering... for example, when pressure-treated wood is shipped to the lumberyard in stacks, they are tightly bundled and damp... sometimes even wet. If you then go and pick through a bin of pressure-treated wood, you will see some pieces are straight, and others moderately to wildly warped. The warped pieces are invariably the pieces that were on the outside of the bundle... exposed to the sun and air causing a rapid drying process that causes the warping, cracking and splintering... In sheds, garden buildings and fence panels the warping is less noticeable but the effects of the elements on pressure-treated wood are no different than with ordinary wood.
This means that a weather preservative is a must, and should be applied as soon as possible after your project is completed which will protect the lumber from less shrinkage occurs and the surface of the wood remains smoother longer.
Be sure that the preservative you purchase is recommended for use with pressure-treated wood.
Stains first...According to sources at Cuprinol, you should wait at least one to two months before staining but many manufacturers carry full lines of both oil and latex products that can be used on pressure-treated wood. You can apply a clear preservative immediately, but it must be a product manufactured for use on fresh pressure-treated wood.
What about painting?Don't even think about painting FRESH pressure-treated wood! The moisture in it means that you will not get good paint adhesion to the wood. Seal your project with a pressure-treated wood preservative immediately. Follow the preservative's instructions regarding future painting, making special note of the amount of time the preservative should weather before painting.