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The question "How do I get sprinklers to work?" gets asked so often, I decided to make a quick but clear tutorial.
Guide To Sprinklers
Step 1: Grid Placement On
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The trick to setting up your sprinklers perfectly, is placing the plots with grid placement on and the sprinklers with grid placement on.
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Go into your menu, click settings and check Grid Placement.
Step 2: Place The Plots
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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.
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Step 3: Grid Placement Off
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Go back into your settings and turn grid placement off.
Step 4: Place The Sprinklers
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With grid placement off, you can hover the sprinkler over the spot until you see a sprinkler icon appear.
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Icon up means the sprinkler will water that crop.
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Same goes for silver sprinklers...
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... and gold sprinklers.
No icon, no sprinkling!
Source: https://gameplay.tips/guides/6274-garden-paws.html