Organic Gardening Supplies: Fertilizers, Pest and Weed Control, Lawn Care

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Choosing Between Drop and Broadcast Spreaders
There are two common types of lawn spreader: drop or broadcast. The
drop spreader is a familiar sight at garden centers and hardware stores. If you are a homeowner with less than 5,000 sq.ft. of lawn area, an inexpensive drop spreader may be all you need. Drop spreaders tend to be more manueverable in tight, awkward spaces and are relatively easy to use.

Broadcast spreaders throw the material out in a wider swath, sometimes as wide as 8'. If you have a large area to cover, they can make short work of it. They are, however, a little trickier to use, since you need to keep up a steady walking speed (usually 3 mph) and you need to be moving when you activate the spreader. It's also harder to get a clean edge, although some broadcast spreaders come with side deflectors, which let you get close to side-walks, beds and driveways without spreading material on these adjacent areas. There are also small, hand-held broadcast spreaders suitable for smaller areas.

Calibrating Your Spreader
It is always a good idea to calibrate your own spreader, even if the manufacturer provides guidelines for setting the spreader with different products. It's easy to calibrate and, if you make a note of your results, you only have to do it once for each product. Here's an example:

Step-by-Step Procedure Example
  We want to apply fertilizer at a rate of 20 lbs per 1,000 sq.ft. The fertilizer comes in a 50 lb bag.
Take a sheet of plastic or a tarp (ideally something bigger than 10' x 10' but smaller will work too) and lay it on the ground. If it's breezy, put something heavy on each corner to keep it in place.  

If your surface is big enough, measure and mark an area of 10' x 10' on the surface. An area of 10' x 10' ideal because it makes the math easy, but it could be any dimension that gives you a convenient square footage number - 5' x 10' or 5' x 8', whatever you care to make it.

In our example, our area is 10' x 10' or 100 square feet
Set your spreader to the setting you think will give you approximately the application rate you want. If the material you want to spread is coarse and granular (for example, corn gluten meal), set the spreader as wide open as it will go. Don't worry about getting it right because you can adjust later. Our fertilizer is fairly coarse, granular material so we open it up about 3/4 of the way.

Empty a small amount of fertilizer or other material into the spreader and run it over the area you marked off as if you were making an application to your lawn.

We pour about 10 lbs of fertilizer into the spreader.
Carefully gather up the material you spread on the surface.  
Take a container of some kind (you'll use it to weigh the fertilizer you just spread) and weigh it and using a household scale. Our bowl weighs 8 oz.
Pour the material you spread into the container and weigh it again. Bowl plus fertilizer weighs 32 oz (or 2 lbs)
Subtract the weight of the container. Total weight (32 oz) minus weight of bowl (8 oz) = 24 oz (or 1.5 lbs).
Calculate the conversion factor for 1,000 square feet. (1,000 square feet divided by the square footage of your test area). 1,000 square feet divided by 100 square feet (size of our test area) = 10. Our conversion factor is 10.
Calculate the application rate of your spreader for the current setting, using this material. Multiply weight of applied fertilizer by conversion factor. Weight of fertilizer (1.5 lbs) multiplied by conversion factor (10) = 15 lbs per 1,000 sq.ft.
Adjust the spreader setting according to your results.

In our example, we want an application rate of 20 lbs per 1,000 sq. ft., so we have two options.

We can either open up the spreader a bit more to get the target application rate or we can close the spreader a little and plan on making two passes with the spreader at half the recommended rate.

Write down the results so that next time you'll know exactly what setting to use for this particular product.  

Using Your Spreader
Follow the specific spreading instructions that come with your spreader. When working with spreaders, always load a spreader on a surface where an accidental spill can be cleaned up and won't matter (driveway, walkway, etc).

Common practice is to first run the spreader around the periphery of the area you are treating; this ensures a consistent application around the edge of your lawn. Next, you run the spreader back and forth within the area bounded by your first perimeter run. Always allow on overlap to avoid missed streaks or "holidays". Ideally, apply your material at half the recommended rate and make two sets of runs, first back and forth in one direction, then again another set of runs at 90 degrees to the first set. This ensures a good consistent coverage and it compensates for any uneven patches.

Clean-Up and Maintenance
The professionals usually say that, after using a spreader, a thorough dry cleaning beats a sloppy wet cleaning any day. It's certainly a good idea to empty your spreader completely and shake out or remove with a brush any remaining material. Keeping moving parts lubricated helps too.