Test your soil to determine the precise application rate you need. UMaine soil scientist Bruce Hoskins says, “We recommend fine granular Sulfate of Potash for high tunnels. It will dissolve and release more completely, when tilled in, than the coarse granular material. This is a particular problem in tunnels due to dry zones between drip lines. If the granules don’t get wet, they will not dissolve and become available to the crop.”
If your soil has a potassium deficiency, you will likely need to apply 200–500# per acre, or 5–10# per 1000 square feet.
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