One of the many benefits of teaching is the constant inspiration from my students. Lately I've been noticing some lovely north arrows on their landscape plans, which spurred the illustration below.
North arrows are an important part to the overall landscape plan drawing. Knowing the cardinal directions gives hints into the location of the shadiest and sunniest locations of your site, plus where chilly winter or steamy summer winds will enter.
I prefer to have the north side of the site plan facing up, but also know that isn't always possible depending on the size of your paper and how the site fits into it. In the end, just make sure the north arrow is pointing in the correct direction.
Some suggestions regarding north arrows.
1. Make sure the north arrow and site plan align (is the north arrow pointing in the same direction as north on the plan? Seems obvious, but you wouldn't believe how often this doesn't happen!).
2. Keep the graphics for your north arrow simple (some of my examples above probably break this rule...I couldn't escape illustration mode!). Overall, just make sure your north arrow doesn't outshine your landscape design.
3. Place the north arrow where it can be found easily...in the title block or near the site plan. I typically place it in the bottom right of the sheet.
4. Keep it at a reasonable size so it can be seen, but once again, doesn't overpower your drawing.