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Last night I started putting together a mixture of soil for blueberry plants. This mixture includes:

garden soil
organic mushroom compost
sphagnum moss

(I also have pine bark mulch to help keep the acidity of the soil)

I have some soil acidifier that I can add. So I want to test the mixture to have an idea of how much I would need to add.

So what I'm wondering, is if I test this soil mixture, how accurate would the results be? I can't imagine that I would be able to get an equal parts of each soil when I test it. Is the only answer to test the mixture several times and average the results out?

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I don't understand your concern. Are you worried you won't be able to mix all the ingredients properly and you'll accidentally scoop up just one of the ingredients? –  Philip Aug 14 '14 at 17:09
@Philip I re-worded the question. I'm trying to gauge how much soil acidifier I would need to add, but I need to be able to know the whole composition of the soil in order to know how much to add. –  The Flash Aug 14 '14 at 17:24
Related: Should I do a soil test before or after amending soil? (where I also advocate taking multiple samples for one test). –  J. Musser Aug 14 '14 at 22:05

2 Answers 2

up vote 4 down vote accepted

Here's my take on it for what it is worth:

Soil is (hopefully) a living, dynamic system whose composition is anything by homogeneous. The pH of one scoop of soil from one part of my garden is likely to have a slightly different pH than that of a scoop from another part of the garden. Similarly, other metrics I might collect on the soil will likely differ as well, though probably not significantly unless I'm purposefully trying to push the pH in one bed toward the more acidic side of the scale or toward the base side of the scale. Variation, probably slight, is to be expected though it is possible that the testing conducted might not indicate much of a difference.

The thing is that anytime you do a pH analysis (or any analysis for that matter) of the soil, you are taking a representative sampling of the overall soil. You're not checking the entire bed. The idea is that the sampling will provide you with adequate information to determine what, if any, changes need to be made to effect a desired change in the soil composition. So, if I am concerned about a pasture's health, I'll collected samples from several sites in the pasture and send it off to the Virginia Ag extension folks and they'll test those samples and provide guidance based on their findings. This is based only off the samples collected but the point is that those samples will provide a pretty clear picture of the whole.

My advice is to mix your soil well and then test and trust that the testing will provide you with accurate information for the bed as a whole. The soil isn't homogeneous but it doesn't need to be either. As long as you are thorough in your mixing of those components, any sampling you do will be good enough for the entire bed. If you doubt that, then take several samples from various positions and average.

That's what I do, when I concern myself with soil pH. With blueberries, which thrive in the more acidic range, pH is important but getting the components mixed will yield you samples that are accurate enough.

One more thing to remember - everything that you put in the garden may vary itself in its pH a bit - peat is a natural product and it will vary a bit. The good thing is that plants are resilient and as long as you are in the pH range, everything will work out great.

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This question has a very simple answer:

If you mixed the soil well, take small samples from several spots in the soil, and mix them well for testing. The results will be accurate. I usually take 1-2 samples per 100 sq. ft., but you can do more if you want the most accurate average. Using multiple samples per test can also be done before laying down the soil, but I don't see that that's necessary.

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