A lot of gardeners test their soil and never use the information, so I know what you mean about it not really being necessary.  I generally only send a soil sample off to be tested if I have a reason to.  Specific testing purposes might include (from most to least important for me):

You want to plant blueberries or something similar in average soil.  If you're going to need to change the pH of your soil, it's good to have an idea of how acid or alkaline your soil is at the moment.

You want to get an idea of how you're improving (or worsening) your soil over time.  I like to look at the percent organic matter and CEC of my soil because these figures are (hopefully) going up every year.  This is generally just interesting, but can be important in permanent perennial systems (like pastures) where you never really see the dirt, so you can't just guess based on on color and texture.

You plan to remineralize your soil.  If you believe that ratios of nutrients are just as important as the absolute amounts (which I'm on the fence about), you'll need more solid data before you can add minerals to your soil.

You're concerned there may be a slight deficiency that isn't showing up in your plants.  Most soils are lacking in something (related to the remineralization concept above).  Your plants might just slow down a bit due to a mild deficiency, but if you're getting most or all of your nutrition from homegrown food, then a mild deficiency in your plants could turn into a mild to moderate deficiency in yourself.  You might not care much if your plants are only operating at 80% efficiency, but I'll bet you care if your kids are.

You think your soil might contain heavy metals.  A one-time soil test is probably worth doing if you live in a city or have some other reason to believe your soil might have heavy metals present above the recommended levels.

You see some kind of nutrient deficiency in your plants, but can't figure out what it is.  Even though you can tell some problems apart visually, others look pretty similar.  If you're a large-scale farmer, you might even choose to take a plant tissue sample in this situation instead of a soil sample.

You are a chemical farmer.  If you're buying any kind of chemical fertilizer, you should definitely get your soil tested first and see how much of it you need.  On the other hand, if you fertilize with compost, this isn't so important.

There are probably other reasons you'd want to test your soil, but those are the first ones that come to mind.  What would you add to the list?

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.



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