Beginning Home Soil Testing

I had been wanting to test our garden soil for a while, so it caught my attention when I saw a soil testing kit at Blain’s Farm & Fleet. The Luster Leaf Rapitest Soil Test Kit said it contained 40 tests: 10 each for pH, nitrogen, phosphorus, and potash. With a $10 off coupon in hand, the $13.99 price tag went down to $3.99. This sounded like a great deal compared to a soil test from the University of Wisconsin’s Soil Testing Laboratories at $15 per sample (which includes the percent of organic matter instead of nitrogen). Let’s see… 10 professional soil tests: $150, or 10 do-it-yourself soil tests: $3.99. Why not?

Test kit and soil samples.

Test kit and soil samples.

What did I test?
I collected four soil samples:
* A – Vegetable Garden
* B – Nightshade Garden
* C – Patio Garden
* X – Purple Cow Organics Activated Compost

To collect the samples, I used a trowel to dig 4 inches down and then put some of the soil into a paper cup. I labeled the cups as I went and tried to avoid any cross contamination.

Was the testing easy?
Although it wasn’t exactly difficult, there were frustrations. I like to do things with precision, so I tried to follow the instructions exactly. But there were challenges with small and wobbly components, lack of detail in some instructions, steps requiring additional equipment, and waiting periods which made the process accident-prone and tedious.

First, manual dexterity was a challenge. I have small steady hands, but yikes! The tiny capsules were difficult to open and the powder had to be carefully inserted into a narrow test chamber. I found the only way to avoid powder poofing onto the table was to loosen the capsule slightly, hold it over the test chamber, steady my hands on the container, and then gently and slowly open the capsule within the narrow space so the powder would fall straight down. This worked ok, except that the color comparator containers are narrow and tipsy as well. There weren’t any major spills but I had to get powder off the table in a few instances and I held my breath whenever the containers wobbled.

The soil testing equipment took over our kitchen table. Here I was opening a capsule over the test chamber of the color comparator container.

The soil testing equipment took over our kitchen table. Here I was opening a capsule over the test chamber of the color comparator container.

Second, some of the instructions could have been written with more detail. For example, what is the best way to get a soil sample 4 inches deep? Is that the top or bottom of the soil collected? Do you measure including the layers of mulch/compost added on top? How much soil should be collected (later I realized it would have been nice to have more)? How should organic matter be sifted out? I read on Amazon reviews that the Luster Leaf company does not respond to inquiries, but perhaps consulting a soil expert at the University, their online instructions, or a Master Gardener could help answer some of my questions.

Third, it would have been nice to have a list of recommended equipment. I found myself contemplating how to do many of the steps because I don’t have lab equipment sitting around the house. I ended up using: a trowel, paper cups to hold the samples, a plastic fork to break up soil, kitchen measuring cups to measure soil, canning jars to mix soil and distilled water, and q-tips to clean the containers. Hopefully the equipment I chose was appropriate.

Fourth, the whole process took a long time. Although this was my first time doing these soil tests, four soil samples with four tests each took at least 5 hours over 4 days. This included collecting the soil samples, performing the tests, and washing out the equipment after tests. I combined steps and waiting periods whenever possible to save time and effort. The waiting periods included: waiting for the soil samples to dry out (about 24 hours), waiting for the soil to settle after mixed with water (30 minutes to 24 hours), and waiting for the tests to change colors (1 minute for pH, 10 minutes for nitrogen, phosphorus, and potash). I put all the equipment in a boxtop so that I could get it out and put it away as I found time to work on it.

What were the results?
The test results found mostly neutral pH and strong deficiencies and surpluses of nutrients. I wouldn’t be surprised to see low levels of nitrogen on a city lot, but I have a hard time believing that my garden soil (with many worms, nitrogen-fixing cover crops, and healthy-looking plants growing) doesn’t have any nitrogen. Or then again, perhaps the nitrogen is only in the top 3 inches of soil and the sample missed it. It would be interesting to send the same soil samples to the University for a comparison since I can’t say I completely trust these results.

Soil Sample pH Nitrogen Phosphorus Potash
A – Vegetable Garden 7.0 (neutral) Depleted* Depleted* Surplus
B – Nightshade Garden 7.0 (neutral) Depleted* Depleted* Surplus
C – Patio Garden 7.5 (alkaline) Depleted Surplus** Adequate
X – Purple Cow Organics Activated Compost 7.0 (neutral)*** Surplus Surplus** Surplus

* Result not confident. Solution may have needed further uninstructed shaking after color settled.
** Result not confident. Solution may have been shaken too much to dissolve settled colors.
*** Result not confident. Color of the solution not obvious when checked against comparator chart.

Nitrogen, phosphorus, and potash tests required mixing soil with water and then testing the water

Nitrogen, phosphorus, and potash tests required mixing soil with water and then testing the water

The pH testing required less soil and was quicker

The pH testing required less soil and was quicker

How confident are you in the accuracy of the results?
Overall based on color changes and results, my gut feel is that I was somewhat confident in the potash results, but not very confident in the pH, nitrogen, and or phosphorus results. Some of the solutions changed color immediately and very clearly, but some colors didn’t change at the noted 10 minute period of time or didn’t accurately match one of the colors on the comparator chart. For the nitrogen and phosphorus, I noticed that there was color settling at the bottom of these containers, so I shook them again and reviewed them after 20 and 30 minutes. In some cases, the color got darker as more of the settled color dissolved. As it was not in the instructions to do additional shaking or waiting, I’m not sure if the color at the 10 minute mark was accurate or whether the color failed to display correctly until the 30 minute mark. When testing the compost sample for pH, a blueish tint did not correspond to one of the shades on the comparator chart.

Even though I don’t find the results dependable, the soil testing was educational and fun. It helped me become more acquainted with the process and gave me the opportunity to think about and question factors influencing the results. If I go with professional soil testing, I will appreciate the service much more now, knowing all the steps involved.

The greatest value is in having accurate and helpful results. This makes professional soil testing for $15 per sample a better deal than the Rapitest do-it-yourself kit for $13.99. You don’t save much time per sample as you would still need to collect soil, fill out a form, and deliver the sample, but you wouldn’t need to fidget with small capsules, make a mess in your kitchen for days, and strain to interpret the results. Otherwise, if you want to try other do-it-yourself methods, there are a few articles online that suggest pH can be tested at home with vinegar, baking soda, or cabbage juice… But in the end, if you want certainty, go with a professional soil test.


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