I just checked with DOFMaster. If you were to use the kit lens, at 18mm, f/8, and focus a mere 7.1 feet away, everything from 3.54ft to infinity will be in focus. Which a fairly depth of field.

Some lenses require stopping down to get sharper images, but even fairly low grade lenses are fairly sharp by f/8, so I don't see why you'd need a narrower aperture... at 18mm. You'll want narrower apertures for macro, and for longer focal lengths.

Doing the same check on DOFMaster with the 85mm lens, at f/8, I need to focus atleast 154ft away to get infinity in focus, and as near as 77.6 feet would also be sharp. To get a more reasonable front distance to what's in focus, you'll need to stop down, well past f/8. Dropping to f/22, and focusing at 56ft, brings 27.9ft to infinity into focus. F/32 and focusing at 40ft, gets you 19.8 to infinity.

So, depending on your lens's sharpness, and it's focal length you may need large f values, but for wide angle landscape, f/8 should be plenty.