Calibrate your spreader

The method

Weigh, spread, weigh again

1. Mark a test area

   For a rotary (broadcast) spreader, mark 1,000 sq ft: 10 by 100 ft or 20 by 50 ft. For a drop spreader, use 100 sq ft (5 by 20 ft) on a garage floor or driveway, so you can sweep the product up.

2. Weigh the product

   Load a weighed amount into a rotary spreader; UF/IFAS uses 20 lb. With a drop spreader you will weigh what you sweep up instead.

3. Make one pass

   Start at the setting printed on the bag and walk at your normal pace. The bag's setting is only a first guess for your spreader.

4. Weigh again

   Weigh what is left in the hopper and subtract it from what you loaded, or weigh what you swept up. That is what one pass put down.

5. Adjust and repeat

   Open or close the setting a step and test again until you land within about 10% of your target.

Good to know

• Calibrate for each product and each person. UF/IFAS advises calibrating for every material and every operator, even when two products have the same numbers, because granules and walking speeds differ.
• Check a rotary spreader's pattern. Lay a row of shallow pans across your path, make a few passes, and compare what lands on each side. Adjust until both sides match.
• Drop spreaders and coated products. A drop spreader's agitator can damage coated slow-release granules; UF/IFAS suggests using drop spreaders mainly for soluble products.
• Once it is set, any lawn size works. A calibrated spreader puts down the same amount per 1,000 sq ft everywhere, so the calculator's spreader target is all you need.