If you want to understand what your garden needs, a soil test can measure soil health and nutrients to identify any deficiencies. We tried a popular do-it-yourself home test with a lab test to see how they compare.
If you want to enrich your soil, use these tips to add your own compost.
Do I Need a Soil Test?
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If you are like me you started gardening for a love of plants but soon learned that the key to successful growing is healthy soil. Good plants cannot overcome poor growing conditions.
If you have a thriving garden that you routinely replenish with rich compost (decomposed organic matter) you many never need or want to have your soil analyzed.
But, when plants are struggling or there is a fear of soil contamination—particularly in vegetable gardens— a test report should help.
Soil tests are used to measure essential elements in our garden beds and identify any imbalances. You may find you have a pH issue or a deficiency that makes it difficult for plants to grow.
Popular advice has us adding all sorts of amendments to our gardens without even knowing what the problem may be. You can save money and frustration by getting your soil evaluated and learn exactly what it needs.
Related: How to Make Worm Tower for In-Ground Composting
Garden Soil 101
Soil | The foundation of your garden. Know what you’ve got and provide only what it needs.
• Mulch | Add 2-inches of organic matter to protect soil, retain moisture, and gradually fertilize your soil.
• Leaves | Finely chopped fall leaves make excellent mulch.
• Compost: Decomposed organic matter providing nutrients for the garden.
• Potting Mix | Contains no soil: designed to optimize plant growth in pots.
• Seed Starting Mix | A lightweight potting mix for sowing seeds in containers.
• Soil pH | Knowing your level (which may vary) is informational, not a call to action. Most soils fall in the range of 5 to 8 and accommodate a wide range of plants.
Soil Testing Options
Soil can be tested with a do-it-yourself kit or by a laboratory.
We tried both and found that the home kit was either imprecise or inaccurate (see below—it is not worth the money).
A lab has the equipment needed to perform accurate tests but the one we used provided a report that required some research to interpret it. I hope your lab is more helpful. You can read about our experience below.
Ideally you will find a lab that is user-friendly for home gardeners so you not only get valid measures but specific and practical recommendations for improving your soil.
Some states provide free soil tests and you may also have a university extension office to provide guidance.
What Soil Tests Can Measure
You can get a soil test to measure just about any compound or mineral in your soil including organic matter, total salts, macro-nutrients, micro-nutrients, contaminants, and soil pH level. But very few of these are likely to be included in a basic lawn and garden soil test that labs offer.
Be sure to read the lab’s description of what’s included with your test, because it varies from lab to lab. The ones that are nearly always included are marked with an asterisk.
Nitrogen may be the most important nutrient in your soil, but it doesn’t stay in the soil, so a lab won’t be able to measure it with a basic soil test.
General
- pH*
- Electrical conductivity (total salts) mS/cm
- Organic matter (% dry)*
Micro-nutrients
- Calcium (Ca)
- Copper (Cu)
- Boron (B)
- Iron (Fe)
- Manganese (Mn)
- Magnesium (Mg)
- Sulfur (S)
- Zinc (Zn)
Macro-nutrients (NPK)
- Nitrogen (N)
- Phosphorus (P)*
- Potassium (K)*
Contaminants
- Aluminum (Al)
- Arsenic (As)
- Barium (Ba)
- Cadmium (Cd)
- Lead (Pb)
- Mercury (Hg)
Soil pH Notes
The pH scale measures how acidic or basic a substance is. The greater the concentration of hydrogen ions, the more acidic it is.
- Knowing your soil pH is really just informational, not a call to action.
- The pH level affects many things including how plants take up nutrients and grow but most of us do just fine never knowing it.
- Most soils fall in the range of 5 to 7.5.
- A reading of 7.0 is neutral, below that is acidic, higher than that is alkaline.
Some plants do better in soils with low pH—like blueberries—and some do better with high pH—like cucumbers, but most plants will grow fine in the 5.5 to 7.5 range if their other basic needs are met.
Changing soil pH for an entire garden is not possible. It would be like trying to change the color of the ocean. It’s much easier to grow plants that like the type of soil you have. Or use containers for those special circumstances.
Buy pH Test Strips | Amazon
Soild pH Tip
Are your bigleaf hydrangea flowers blue—and do they stay blue year after year?
That’s a sign of soil acidity (with aluminum available).
Macro-nutrients N-P-K
These are the same nutrients listed on commercial fertilizers: nitrogen (N), phosphorus (P), and potassium (K). All soil tests focus on these.
Since a lab can’t measure your soil’s nitrogen levels with a basic soil test, they may provide a general nitrogen level common in your region.
And, again, if your garden is doing fine, the test really isn’t necessary.
Testing of micro-nutrients and contaminants will likely require extra payment.
Home Soil Test Kits Versus Laboratory Tests
We did two soil tests: one using a do-it-yourself home soil test kit that can be purchased at any home and garden store, and one from an accredited lab near us that specializes in soil testing for farms.
We were curious to see how the two types of tests compared and learn more about our soil.
The soil samples for both tests were taken from the same location in the garden at the same time. If you can afford it, it is recommended to have several samples tested from various parts of the garden to get a better overview.
We did not like the home kit at all. We only tried one (ordered from Amazon) but it was awkward to use and the results were not accurate or specific enough. We do not know of others that are more reliable.
Soil analysis at the lab, while more accurate, was focused on calculating N-P-K ratios to help you select the right fertilizer (if you’re a fertilizer user) and the amounts to apply.
This may be what some gardeners want, but we were disappointed that the numbers we received weren’t given much interpretation. We had to do a lot of digging around on the internet to understand them.
Related: Biochar as a Soil Amendment (Pros and Cons)
1Rapitest | Soil Test Kit | $20 + tax
Home Soil Testing Kit | Amazon
- Tests pH, nitrogen, phosphorus, potassium.
The kit comes with little testing capsules that are dissolved in distilled water and measured against a color chart.
The directions were not easy to follow and sometimes made no sense.
Example
“Allow color to develop for 10 minutes. Do not allow the color to develop for more than 10 minutes.”
That’s a rather strict timeline!
Some of the capsules were impossible to open without creating a mess (and wasting a test).
The phosphorus test would not dissolve as needed and the results were difficult to decipher.
Bottom Line
Frustrating to use, clunky supplies, vague or inaccurate results. Not worth it.
Without the proper lab test (below), we would not have known how inaccurate this test was.
2Lab Test | $45 + shipping
We sent the required amount of garden soil to the lab in a clean, plastic food bag via the postal service.
The basic fee included testing of:
- Electrical conductivity (total salts) mS/cm
- Organic matter % dry
- Phosphorus (extractable) mg/L P
- Magnesium (extractable) mg/L Mg
- Potassium (extractable) mg/L K
- pH
Bottom Line
It was interesting to have some basic measures of our soil but our expectations for the report were not met.
This particular lab caters to farmers and the reports are not easy for average home gardeners like us to understand.
Again, the recommendations were for commercial fertilizer applications and nothing else.
We now know there is a potassium deficiency in our soil but how that is managed will require our own research.
If you are doing a lab test, get recommendations or find reviews first. Learn what they will be testing for, ask to see report examples, and how the information will be interpreted. You may even have a local cooperative extension to assist you.
Related: Will Pine Needles Make My Garden Soil pH Too Acidic? (No, It’s a Myth)
Conclusions
Would we use a home test kit again? No.
Would we send soil to the lab again? Yes, if we feel the need and can find one that provides more thorough/practical advice based on the findings. If we had any concern about contaminants, we would definitely get that special testing done.
The best advice is to continually replenish your soil with compost but never add other amendments without first knowing if they are needed. One example is the unnecessary use of Epsom salts in the garden. Otherwise the excess goes to waste and can potentially harm the environment.
Resources
- UMass | Interpreting Your Soil Test Results
- PSU | Soil Testing Tips
~Melissa the Empress of Dirt ♛
