The trick to setting up your sprinklers perfectly, is placing the plots with grid placement on and the sprinklers with grid placement off.

Go into your menu, click settings and check GRID PLACEMENT.

With grid placement on, it becomes rather easy to place well-aligned plots.

For this tutorial, I'll place one, two and four plots for a copper, silver and gold sprinkler respectively.

Go back into your settings and turn grid placement off.

With grid placement off, you can hover the sprinkler over the spot until you see a sprinkler icon appear.



Icon up means the sprinkler will water that crop.

Same goes for silver sprinklers...


... and gold sprinklers.


No icon, no sprinkling!

The same strategy holds true for planters.

when placing the planters:



when placing the sprinklers:



The only down-side is that the sprinklers seem to snap onto the planters a little bit too high.



Lowering the sprinkler with the shifter solves that issue.

You can shift the sprinkler down halfway into the ground and it will still work:



Any lower, though, and it won't sprinkle the plot.