Why are there two kinds of spreaders and which one should I get? This is not a question of product recommendation, but rather, which kind of spreader is more popular and why? Or should I have one of each?
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I was hoping to score the popularity vote on the comments below (if I may). Please vote for which type of spreader you prefer (or if you prefer both, then vote for both).– Ben WelbornCommented Jun 28, 2016 at 18:40
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I prefer Broadcast spreaders.– Ben WelbornCommented Jun 28, 2016 at 18:40
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I prefer Drop Spreaders.– Ben WelbornCommented Jun 28, 2016 at 18:40
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1 Answer
The main difference is uniformity vs speed.
Most broadcast/rotary spreaders spread quickly (high volume, low accuracy); in other words, the average broadcast spreader typically spreads about triple the rate of drop spreaders. So for many products with a low application rate (usually pesticides and fertilizers) you may spread too much (here and there), or have a little accident where you ran out too soon with a broadcast spreader. Essentially you can't accurately adjust/calibrate rotary spreaders which is important for some lawn chemicals (like like 30-0-0 fertilizer, soil acidifiers, and pesticides), which need to be applied with a little care.
The biggest drawback with broadcast spreaders (besides applying too much) is knowing the true application rate and achieving uniform application. Drop speaders are better for that.
Drop spreaders easier to calculate and calibrate because you can measure the width of the spreader, and trust that the spreader is dropping granules uniformly, regardless of the speed at which you walk.
Width multiplied by the length of the pass equals the (applied) area. Calibrating say a 24" spreader by putting a couple of pounds of some product that covers (for example) 7000 sq. ft. per 20 lbs in it and walking 350 ft is how you calibrate a drop spreader (easy). At the end of 700 ft you should be out of this product. If you ran out early, then you need adjust the spreader settings to close the aperture... or if you have product leftover, then open the aperture.
The better way to calibrate a broadcast spreader is to set out a pan and walk over it (at a certain pace), then weigh the contents of the pan and divide the area by the weight (sounds easy). However, the width and rate of application is variable (often more material lands along the edges of the application path) and it's simply more difficult to measure and calibrate (it's not really accurate without painstaking efforts).
The biggest drawback to a drop spreader is that it will be slower and will (almost always) require more passes (walking back and forth) than a broadcast spreader. If you are applying something like grass seed, you could apply it with a drop spreader, but it will probably take three times longer.
Check out the calibration methods from Penn State U..