Here's my layout. The only oddball is that the plants immediately above and below the the sprinkler are planted at half-facing (/ or \). This keeps my Sim from giving me the "can't get there from here" argument when I put him to work. ("w" is the wall)
wwwwwwwww
-xxxxxxxxxxx-w
w
-xxxxx-xxxxx-w
-xxxxx-xxxxx-w
s s w
-xxxxx-xxxxx-w
-xxxxx-xxxxx-w
w
-xxxxx-xxxxx-w
And then repeat the pattern to a total of four sprinklers. I left room to expand to the left, which would about double the size of the garden area, but considering the amount of maintenance time this much area takes, it's not worth it to me. The spaces in the middle of the rows aren't strictly necessary, so I could have five more plants in there, but they do make getting in and out a bit faster and are a bit more aesthetically pleasing.
